Faculty of Physics and AstronomyUniversity of Heidelberg

Diploma thesisin Physics

submitted byBente Philippsen

born in Heide, Germany

2008

Hard Water or High Ages?14C food crust analysis on Mesolithic pottery

from Northern Germany

This diploma thesis has been carried out by Bente Philippsenat the Institute for Environmental Physics

under the supervision of Prof. Werner Aeschbach-Hertig.

Abstract

The aim of this thesis is the investigation of the hardwater effect and its implications for the dating of thefirst occurrence of pottery in Northern Germany. The hardwater effect denotes the effect of a high carbonatecontent of freshwater on radiocarbon dating: the dissolved minerals can lead to spurious, too high agesof samples from freshwater systems. The possibility of the hardwater effect in food crusts on pottery isinvestigated for two sites of the Late Mesolithic Ertebølle culture. The first radiocarbon dates from the foodcrusts from these sites were surprisingly high. I will examine if the pottery really is so old or if the hardwatereffect is responsible for this. The samples I thus have to analyze are very small. Instrumental developmentwas needed for the dating of these samples. On-line combustion combined with stable carbon and nitrogenisotope measurements is developed to minimize the number of steps in the preparation and measurement ofa sample so a reduction of contamination may be achieved. Also the conversion of the CO2 from combustedsamples to graphite, the form of carbon in which the radiocarbon content can be measured, is examined andsome improvements are suggested and tested.

Abstract

Das Ziel dieser Arbeit ist die Untersuchung des Hartwassereffekts und seines moglichen Einflusses auf dieDatierung der fruhesten Keramik in Norddeutschland. Der Hartwassereffekt bezeichnet die Auswirkungeneines hohen Karbonatgehalts von Flussen und Seen auf die Radiokarbondatierung: die gelosten Mineralekonnen zu falschen, zu hohen Altern von Proben aus Sußwassersystemen fuhren. Die Wahrscheinlichkeitdes Hartwassereffekts in Speiseresten auf Keramik, in der Sußwassernahrung zubereitet wurde, wird furzwei norddeutsche Fundstellen der spatmesolithischen Ertebøllekultur untersucht. Die ersten Radiokarbon-datierungen von Speiseresten auf Keramik dieser Fundorte ergaben erstaunlich hohe Alter. Ich werde unter-suchen ob die Keramik wirklich so alt ist oder ob der Hartwassereffekt dafur verantwortlich ist. Die Proben,die ich dafur analysieren muss sind sehr klein. Um diese sehr kleinen Proben datieren zu konnen, ist instru-mentelle Weiterentwicklung notig. Zum Beispiel soll Fraktionierung minimiert werden. Die Verbindung derProbenverbrennung mit der Messung von stabilen Isotopen wurde entwickelt um die Anzahl der Probenauf-bereitungsschritte zu minimieren. Dieses kann zu einer Reduzierung von Verunreinigungen der Probe fuhren.Die Umwandlung des CO2 zu Graphit, der Form von Kohlenstoff in der der Radiokarbongehalt gemessenwerden kann, wird untersucht. Einige Verbesserungen dieses Prozesses werden vorgeschlagen und getestet.

Preface

The influence of the hardwater effect on pottery dating, the necessary methodological and instrumentaldevelopments, and the influence the hardwater effect has on the dating of the first pottery in NorthernGermany will be presented in this thesis. The hardwater effect is the influence of dissolved carbonate onsamples from freshwater systems. It is a long-known and broadly accepted phenomenon. However, thepossibility of a hardwater effect in one sample type is still under debate. Food crusts on pottery in whichfreshwater food such as fish was cooked could as well show spurious ages if the freshwater food came fromwater systems with a high carbonate content. So far, this effect has not been agreed on. I have thereforechosen two sites next to freshwater rivers in Northern Germany where a hardwater effect on food crustson pottery is probable. I have taken a large number of archaeological samples as well as examined recentfreshwater samples in order to obtain statistically significant results. As the food crust and fishbone samplesfrom these sites are very small, development in sample processing methods was necessary. A device combiningsample combustion for AMS 14C dating with on-line stable isotope measurements was advanced and tested.This device has the potential of reducing the number of steps in sample preparation, the contamination risk,and the total sample size.

Due to various problems with the ion sources and tandem accelerator, some of the samples could not bemeasured before this work had to be finished. A new ion source was constructed and it was planned thatmy samples could be measured using this new ion source. Because of several delayals, it was not possibleto start the new ion source for standard 14C datings before this thesis had to be finished. Therefore, theold ion source was used for my samples. There are two disadvantages with that: First, the old ion sourceis not able to produce enough ion beam current for dating when the samples are very small. Second, theion source is only optimised for samples graphitised with cobalt at 700◦C. My small archaeological samplescould thus not be measured at all. Normal-sized samples graphitised with iron at 550◦C are measured witha far higher uncertainty than would be the case in the new ion source.

Working in the intersection of physics and archaeology

The topic lies in the intersection of physics and archaeology, an area which is also called archaeometry .

• “Archaeology is the study of the human past through material remains” (Hayashida 2003).

• “Physics is the study of matter and energy and how they work with each other”(http://simple.wikipedia.org/wiki/Physics on February 26, 2008).

Archaeometry is thus the (e.g. physical or chemical) analysis of material remains to study the human past.Archaeometry is another term for archaeological science and comprises different scientific technologies whichare applied in archaeology. This can be chemical and physical dating methods, provenance studies of arte-facts, study of the distribution and use of artefacts, reconstruction of past landscapes, climate and envi-ronment, dietary studies of humans and animals, remote sensing and geophysical surveys, and conservationtechniques (Tite 2003a).

This work will deal with two aspects of science applied to archaeology: radiocarbon measurements fordating and stable isotope measurements on food crusts for “dietary” studies. Instumental development

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and examination of the existing sample preparation methods will form the physical part of the work. Atthe same time, it will also deal with the archaeological background on a scientific basis, bearing in mindthe appeal of Dunnell (1993): “The attraction, particularly from the physical sciences side, often seemsto be to the non-scientific archaeology of the Sunday newspapers’s feature section”, and “there will be nobasis for integrating archaeometry and archaeology until archaeometrists focus their attention on scientificarchaeology”. Tite (2003a) also emphasizes this fact: “To ensure that archaeometry remains relevant toarchaeology, it is essential that only real archaeological questions are addressed. This in turn necessitatesthe maintenance of a substantial dialogue between archaeometrists and archaeologists together with a holisticapproach that goes beyond reconstruction to a full interpretation within the specific archaeological contextunder investigation.” On the other hand, archaeologists should be careful not to depend too much onscientific dates. It is tempting to use for example radiocarbon dates as a calendar for prehistory, thus givingarchaeologists the role of historians. But it has to be kept in mind that reporting the archaeological phaseof a site is often more useful for comparing findings in a larger region than expressing the time horizon incenturies BC. Absolute chronology may be the aim of archaeology, but it must never be the backbone in away that a calendar is the backbone of history (Fischer 1976).

The topic presented in this thesis was especially interesting to me as I had gained insight both in physicsand prehistoric archaeology in my studies. During archaeological studies and in physics projects, I couldlearn about physical dating methods and especially radiocarbon dating. In archaeology, I specialized in theNeolithic in Northen Germany and South Scandinavia, particularly in the Mesolithic-Neolithic transition.This made it easier for me to take both the physicist’s and the archaeologist’s point of view when discussingthe sites I examined and their importance in the cultural development of the region. I hope therefore that Ican avoid some of the possible mistakes that happen when two differnent disciplines meet.

Outline of thesis

The first chapter presents an overview over the methods applied. After an introduction to the basic principlesof AMS radiocarbon dating and stable isotope analyses I will describe the method of pottery dating. In thesecond chapter, I will present the development of enhanced techniques for the preparation of small samples.The third chapter will deal with the sites from where I got the samples as well as their geological andarchaeological background. In the same chapter, the events being dated in this thesis will be put into thecontext of cultural development at that time. The fourth chapter will finally deal with the archaeologicalsamples and the recent test samples which all were used to determine the hardwater effect for the two rivers.Many of the physical terms may be unknown to archaeologists and, the other way round, physicist are likelyto be unfamiliar with the archaeological terms. A glossary at the end of this thesis may contribute to abetter understanding for specialists of both fields without lengthening the text.

Acknowledgements

First of all I would like to thank the AMS 14C Dating Center of the University of Aarhus and its director,Jan Heinemeier, for a warm welcome and the opportunity to work on an exciting topic. I was in thefortunate position to benefit both from the laboratory’s equipment and its know-how as well as from itscontacts to scientists of other disciplines. The laboratory technicians Hanne Jakobsen, Ann-Berith Jensenand Vibeke Jensen taught me how to use the equipment, helped me patiently whenever I was confronted withproblems. Together with the graduate students Torben Ankjærø and Christina Maria Lutz they created agood working atmosphere. With Marie Kanstrup, I had inspiring discussions about archaeological andstable-isotope related matters. Egon Jans and Klaus Grossen helped me to build up the new graphitisationsystem. Klaus Bahner, although constantly nagging about adverse conditions, measured my samples in thebest possible way at the accelerator together with his team of accelerator operators. Prof. Dr. Claus vonCarnap-Bornheim, director of the Archaeological Museum of Schleswig-Holstein in Schloss Gottorf, paid 30of the datings and the foundation “Prof. Werner Petersen-Stiftung” in Kiel, Germany, provided the funds

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for this. The choice of the topic gave me the chance to interdisciplinary co-operation with the team ofarchaeologists from the Archaeological Museum. Sonke Hartz was an enthusiastic co-worker and made thefinds from Schlamersdorf available to me. He also organized the pottery experiments together with HarmPaulsen and Aikaterini Glykou and introduced me to a number of helpful people: Manfred Pfeiffer fromNeustadt (Holstein) provided the equipment for the fishing attempts in the Alster. Dr. Rainer Brinkmannfrom Schlesen and Dr. Mattias Brunke from Flintbek helped establishing the contact to Dipl.-Biol. DennisGrawe and Dipl.-Ing. Markus Vainer from Institut BIOTA GmbH who finally caught fish for us in the Alster.Winfried Dobbrunz from Bad Oldesloe provided us with fish from the Trave. A very warm thank you isaddressed to all the archaeologists from Schleswig for receiving me and my project so cordially. My dearfriend Birte Kruse provided a home for me during my visits to Schleswig and accommodated me even whenI returned from the pottery experiments, sooty and smelling of smoke. My flatmate Oline Laursen madesure that I was well provided with victuals for long days at the university – and that it always was niceto come home. This thesis was supervised by Prof. Werner Aeschbach-Hertig in Heidelberg. He providedtheoretical knowledge both about the physical aspects of this thesis and about the formalities of a diplomathesis. Henrik Kjeldsen was my supervisor in Arhus and helped me with all technical and theoretical aspectsof my work. I want to thank him for support and encouragement throughout the time of research and writingas well as for interesting scientific discussions. I want to thank my parents who made it possible for me tostudy a subject of my own choice and who supported me at all times. As English is not my native languageI am thankful for all the help I received concerning the language - both grammar and spelling as well aschoice of words and the correct use of expressions. The dict.leo.org-community provided a great databaseof English expressions and fine nuances of acceptations of words as well as surprisingly fast answers to allmy questions about the English language. Christopher Dege supported me in all my plans and was alwaysthe first reader of my texts. He helped me a lot with critical statements from a linguist’s point of view andcorrected most of the errors in my manuscript. He was also very helpful in all questions concerning thetypesetting system LATEX which was used for producing this paper. I am solely responsible for all remainingerrors.

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Contents

1 Methodology 11.1 Radiocarbon dating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 The history of radiocarbon dating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1.2 Error sources and correction factors in radiocarbon dating . . . . . . . . . . . . . . . . 41.1.3 Dendrochronology and the calibration of the radiocarbon time scale . . . . . . . . . . 5

1.2 Accelerator mass spectrometry (AMS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.2.1 Reporting of 14C data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.2.2 Reservoir Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.2.3 How the hardwater effect works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151.2.4 The hardwater effect in archaeological material . . . . . . . . . . . . . . . . . . . . . . 21

1.3 Isotopic fractionation and stable isotope analysis . . . . . . . . . . . . . . . . . . . . . . . . . 211.3.1 13C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.3.2 15N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

1.4 Food residues on pottery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251.4.1 Terminology and general remarks on prehistoric pottery . . . . . . . . . . . . . . . . . 261.4.2 Dating of pottery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261.4.3 Analyses on food crusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2 Small sample preparation 312.1 Sample pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322.2 Graphitisation of small samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.2.1 Experiments with the existing graphitisation system . . . . . . . . . . . . . . . . . . . 352.2.2 Establishing a new graphitisation system with smaller reactors . . . . . . . . . . . . . 422.2.3 On-line combustion with EA measurements . . . . . . . . . . . . . . . . . . . . . . . . 48

3 The sites 563.1 Geography and research history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563.2 Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

3.2.1 Water hardness and 14C in the Trave and Alster . . . . . . . . . . . . . . . . . . . . . 603.3 Ertebølle and Funnel Beaker culture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

3.3.1 EBK research history and Køkkenmøddinger . . . . . . . . . . . . . . . . . . . . . . . 613.3.2 The environment of the Ertebølle culture . . . . . . . . . . . . . . . . . . . . . . . . . 623.3.3 The Ertebølle economy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633.3.4 Ertebølle pottery and tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643.3.5 Transition to farming: From Mesolithic to Neolithic or from Ertebølle to Funnel Beaker

culture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

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4 The samples from Schlamersdorf and Kayhude 714.1 Selection and pretreatment of samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

4.1.1 Water samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714.1.2 Recent fish and molluscs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724.1.3 Recent food crusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744.1.4 Old food crusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784.1.5 Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

4.2 Dating and stable isotope measurement results . . . . . . . . . . . . . . . . . . . . . . . . . . 834.2.1 Recent samples from the river Trave . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844.2.2 Archaeological samples from Schlamersdorf (Trave) . . . . . . . . . . . . . . . . . . . . 874.2.3 Recent samples from the river Alster . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904.2.4 Archaeological samples from Kayhude (Alster) . . . . . . . . . . . . . . . . . . . . . . 914.2.5 Comparison with marine samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

4.3 Comparison of the sites, discussion and conclustion . . . . . . . . . . . . . . . . . . . . . . . . 95

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Chapter 1

Methodology

In this thesis, I have worked with two physical methods which are routinely applied to archaeological research.The first is radiocarbon dating, a physical dating method that is based on the radioactive decay of the 14Catom. The second is stable isotope measurement, in this case carbon (13C) and nitrogen (15N). Stable isotopemeasurements are used for examining the marine, terrestrial, or freshwater origin of archaeological samplesand for food reconstruction of prehistoric populations. Both methods will be presented here, including theirhistorical development, the principles, applications, and limitations.

1.1 Radiocarbon dating

Radiocarbon or 14C dating is a method of age determination of the last uptake of carbon in a sample, forexample in the form of carbon dioxide from the atmosphere. Therefore, it is in principle suitable for thedating of all organic material. The method can also be used for some inorganic material like carbonates thatare formed from atmospheric CO2. Radiocarbon dating makes it possible to examine ancient cultures fromall over the world which before could not be dated. A reason for the lack of dates can be that writing wasnot known in that culture as is, by definition, the case in all prehistoric cultures. Other reasons include thatthe writing is not yet deciphered as for Maya Yucatan and Etruscan Tuscany or that time was unimportantin an otherwise literate culture such as in India (White 1976). In a culture where time is unimportant,no dates are bequethed. “Radiocarbon dating is probably the technique that has had greatest impact onarchaeology, of particular importance being the investigation of the chronology for the development andspread of agriculture across the world” (Tite 2003a). The introduction of radiocarbon dating as a datingmethod for archaeology was therefore called radiocarbon revolution.

Carbon has three isotopes, 12C, 13C, and 14C. The Carbon-14 isotope is radioactive with a half-life of5730 years. Because of this constant decay rate, it is possible to use 14C for the measurement of the timethat passed since 14C was last uptaken by a sample. 14C decays in the reaction

14C → 14N∗ + β + ν.

As time passes, the amount of 14C decreases while the amount of 14N∗ increases. The 14N is here marked withan asterisk to indicate that it is radiogenic, i.e. originating from the radioactive decay of another element.For calculating an age, one could therefore measure both the 14C- and 14N∗-amount present in a sample. Themore 14N∗ there is present compared to 14C, the more time has passed. Unfortunately, the concentration ofthe decay product 14N∗ in a sample can not be measured. 14N is ubiquitous as atmospheric air consists to78% of nitrogen, and 99.634% of natural nitrogen atoms are 14N. The small amount of 14N∗ being formed ina sample is, as all nitrogen under standard conditions, in gas phase. It thus mixes with atmospheric nitrogenand can not be separated from the 14N that is present everywhere on earth.

The fact that 14C decays with a constant rate, can nevertheless be used for measuring time. This becomes

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clear when we take a look at the exponential decay law that describes the decay of radiocarbon (equation 1.1).

N = N0e− t

τ . (1.1)

From this equation, the time since the last uptake of carbon can be calculated. When the initial concentrationof 14C, N0, and its mean life τ is known, time since death t can be calculated from the following equationafter measuring the present 14C concentration N :

t = τ lnN0

N. (1.2)

This equation is derived from the decay law. The mean life τ of radiocarbon has been measured with sufficientprecision. The present 14C concentration in a sample can be measured with methods which are discussedbelow. Thus, only the initial 14C concentration of the sample, N0, is missing before we can calculate theage of a sample. How is it possible to find the initial 14C concentration, that was present in a sample anunknown time ago?

Dating is made possible because the 14C-content of the atmosphere is reasonably constant. The atmo-sphere’s 14C content in the past can thus be deduced from its recent 14C content. This constancy is due tothe way of 14C formation: The radioactive decay is compensated by the constant production of 14C by cosmicrays in the upper layers of the atmosphere through the reaction 14N(n,p)14C. There is thus an equilibriumbetween formation and decay which results in a reasonably constant 14C concentration in the atmosphere.The formation of 14C is here described in more detail: A neutron which is produced by cosmic rays reactswith Nitrogen-14 which consists of 7 protons and 7 neutrons to form a Carbon-14 nucleus with 6 protons and8 neutrons, and a proton. 14C is the radioisotope with the highest atmospheric production rate: 2.2 atomscm−2sec−1 (Kocharov 1992). About 2/3 of the 14C production take place in the stratosphere and about 1/3in the troposphere. Through the following reaction, 14C and an oxygen molecule O2 react to CO2:

14C + O2 → 14CO + O214CO + OH → 14CO2 + H

It resides for about 10 years in the stratosphere. In the form of CO2, the 14C is being distributed throughoutthe atmosphere and then for example built in by plants through photosynthesis. During its life, an organismincorporates carbon from this well mixed atmospheric reservoir. This is how the constant atmospheric 14Cconcentration leads to a constant 14C concentration in a living organism. When the 14C content of a livingplant is measured now, we can assume that a plant living at any time in the past had the same 14C contentwhile it was alive. With the organism’s death, the carbon uptake ends and the 14C that decays is not beingreplaced by new 14C. So, the 14C content of the sample decreases according to the exponential decay law(equation 1.1, see figure 1.1).

After these explanations, it is clear how the initial 14C concentration N0 of a sample is estimated. Inreality, though, the situation is a little more complex than it was described here, because there are variationsin the production rate of 14C. How these variations were discovered will be described in section 1.1.1. Thesevariations in atmospheric 14C do not nullify the method of 14C dating, as one can correct for them. Howthis correction is made will be described in section 1.1.3.

Now the method of measuring the present 14C concentration in a sample has to be discussed. Theconcentration of 14C can either be measured directly via accelerator mass spectrometry (see section 1.2) orindirectly via decay counting. This is referred to as the “conventional” method. In the first case, N and N0

denote concentrations of 14C; in the second case, they denote activities. The 14C concentration of a sampleis measured as the 14C/13C ratio when accelerator mass spectrometry is used. Details will be presented laterin section 1.2. For decay counting, the number of 14C atoms that decay per time unit is measured. Thenumber of decaying 14C atoms is proportional to the total number of 14C atoms present in the sample. Withmeasuring the mass of the sample, one can convert the measured number of 14C atoms to a concentration,the 14C/12C ratio. In both cases, one can not be sure to have counted all 14C atoms that are present in thesample. The measured 14C concentration in the sample is thus being compared to the 14C concentration ofa standard material with known age. If for example only 10% of the sample’s 14C atoms can be detected,

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Figure 1.1: The radioactive decay of 14C

then also only 10% of the 14C atoms in the standard material can be detected. The limited detection ratioscancel thus each other out. Section 1.2.1 describes in detail how the age of a sample is calculated from themeasured 14C concentrations of the sample and the standard.

1.1.1 The history of radiocarbon dating

After the basic principles of radiocarbon dating have been explained above, I have now chosen a historicalperspective to shed light on the development from the discovery of 14C to the routine measurements oftoday. It will be shown that some of the basic assumptions stated above have proven inaccurate, but thatthis always led to new knowledge and only made the method of radiocarbon dating more reliable in the end.An overview over the early years of radiocarbon dating is given by Suess (1992). A lot of the informationpresented here as been extracted from his work.

The first list of radiocarbon ages for unknown samples appeared in 1951 (Arnold and Libby 1951) afterthe idea had been proposed by Willard Libby in 1946. Two key points lead to the state of knowledge whichprovided the basis for 14C dating. On the one hand, the unstable 14C carbon isotope was discovered in1937 (Ruben and Kamen 1941). It was observed that it was produced by cosmic rays and that it had ahalf-life “between 1,000 and 25,000 years”, thus fitting archaeological time scales (Korff and Danforth 1939).Later, the half-life was determined more precisely to 5568 years, which was used for the first datings. Thishalf-life had finally to be specified over again: In 1962, a more precise half-life of 14C was determined - 5730instead of 5568 years. Even though the half-life was not known exactly, the theoretical knowledge about the14C atom and its deccay was hence available in the 1940s. On the other hand, a few weak counting sourceshad been constructed, and Libby had invented the screen-wall counter. The practical basis was consequentlyalso given. Note that this counter measured radioactiviy. It was thus capable of measuring the number ofdecaying 14C atoms and give the activity of a sample. From 1952 to 1955, 7 radiocarbon dating laboratories

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were established. One of them has to be named specifically: In 1953, the USGS (US Geological Survey)Radiocarbon Dating Laboratory started work with acetylene counters under the leadership of Hans E. Suessand carried out 200 measurements in the first two years. Their most important results were the dating ofthe maximum extent of the North American ice sheet, the result that Homo neanderthalensis survived inselected areas until about 30,000 years ago and the “Suess effect” which was named after its discoverer. TheSuess effect is the anthropogenic drop in 14C activity in air which occurred during the industrial revolution,when 14C-free CO2 from fossil-fuel combustion was added to the atmosphere. This drop in atmospheric 14Cconcentration is one of the reasons for the fact that the initial 14C concentration of a sample in the past isnot the same as the present 14C concentration.

In 1959, de Vries demonstrated the variability of atmospheric 14C over the past centuries. The atmopheric14C concentration is thus not only altered by the Suess effect, that diluted the 14C concentration, but thereare additional variations. Those variations are called “wiggles”. In 1971, Houtermans found out from 350radiocarbon samples that had been dendrochronologically dated that these radiocarbon variations correspondto a line spectrum with a prominent 200-year line. It took a long time until the existence of those wiggleswere widely accepted, and still they are not fully understood. Dendrochronology is the method of tree ringdating. This method provides samples of a known age for testing radiocarbon dating - just as Houtermansdid. When 14C-dating a tree ring of known age, one can therefore calculate the atmospheric 14C activity ofthe time when the tree ring was formed. When this is done for a long stretch of time reaching back in thepast, one can give the initial 14C activity for each year. The plot of this information is called the calibrationcurve, as it can be used for calibrating a measured 14C concentration to obtain a calendar age. This will bedescribed in section 1.1.3.

1.1.2 Error sources and correction factors in radiocarbon dating

As mentioned in section 1.1.1, the 14C concentration of the atmosphere is not completely constant. Thevariations in 14C production that cause the above-mentioned “wiggles” are due to variations in sun activityand the earth’s magnetic field that affect the cosmic radiation. As the cosmic radiation produces neutronsthat, together with 14N, form 14C, the 14C production rate varies according to the variations in cosmicradiation intensity. Two other important effects are anthropogenic: The Suess effect that was described insection 1.1.1 and the bomb pulse. The Suess effect is the depletion of 14C in the atmosphere because of thecombustion of fossil, 14C-free fuels since the industrial revolution.

The “bomb pulse”(see figure 1.2) denotes the increase of 14C in the atmosphere after H-bomb tests duringthe 1960s up to twice the normal activity in the mid-1960s and its decrease since then. The 14C concentrationin the present atmosphere is decreasing exponentially, but with a much smaller half-life than the 14C half-lifeof 5730 years. Not only the decay of 14C reduces the atmospheric 14C concentration. The excess 14C isalso incorporated in the biosphere and in the oceans and so gradually removed from the atmosphere. Themean life of this decay is around 17 years, so that its half-life is approximately 12 years. Because of thisrapid decrease, the high 14C concentrations in samples from the last few decades can be used as a tracerand for high-precision radiocarbon dating (see e.g. Lynnerup, Kjeldsen, Heegaard, Jacobsen, and Heinemeier(2008)).

Variations in the initial 14C activity or content can be calibrated with radiocarbon dating of tree rings ofknown age. The plot “radiocarbon age over calendar years” is called the calibration curve. Unfortunately, insome periods there are ambiguities in that curve, so that it can not be decided which calendar age a certain14C concentration belongs to. Calibration will be explained in section 1.1.3.

As we have seen so far, some basic assumptions were made for radiocarbon dating. These are summarizedin the following list (after Browman (1981)):

1. 14C decays exponentially at a known rate, and the initial measurement of that rate, Libby’s half-lifeof 5568±30a, is adequate enough to make reasonable computations of age

2. activity or 14C content can be measured with acceptable accuracy3. secular constancy of 14C concentration in the atmosphere at one point of the earth4. simultaneity: the 14C concentration is the same for any two points on the earth’s surface

4

Figure 1.2: The bomb pulse in atmospheric CO2 and in the dissolved inorganic carbon in near-surfaceseawater. The annual total testing is given in megatons (Clark and Fritz 1997).

5. the atmosphere is the only source of carbon in living organisms6. isotopic integrity after organism’s death, no material added, 14C/12C changes only by radioactive decay7. all organisms are in isotopic equilibrium with the atmosphere i.e. no fractionation occurs

But we have also seen that these assumptions are not completely appropriate, so corrections have to beapplied:

1. the half-life of 14C is 5730±40 a instead of 5568±30 a, and as data is still published with Libby’shalf-life, ages have to be multiplied by 1.029

2. background corrections and measurement of standards for setting up the instruments; compensationof differences between laboratories because of differences in preparation and evalutation of data

3. calibration curve (see section 1.1.3) because of long term variations, caused by geomagnetic field inten-sity, and short term variations, heliomagnetic modulation of 14C production, of the atmospheric 14Ccontent, which is additionally altered by the Suess effect and bomb tests

4. latitude and altitude effects: samples from the southern hemisphere are 40-80 years “older” than thosefrom the north. Because of different reservoir exchange ratios, the ocean surface on the southernhemisphere is bigger.

5. water plants and animals take carbon from the water; error sources and corrections: see section 1.2.26. contaminants that entered the sample after the organism’s death have to be removed7. fractionation takes place on all steps of the food chain, beginning with photosynthesis and has to be

corrected through 13C/12C measurements (see section 1.3)

1.1.3 Dendrochronology and the calibration of the radiocarbon time scale

Because of the “wiggles” in the atmospheric 14C content (see section 1.1.1 and 1.1.2), the assumption of aconstant atmospheric 14C concentration is wrong and the radiocarbon ages have to be calibrated to correctfor the variations in atmospheric 14C content. For calibrating the radiocarbon ages, one needs samples ofknown age. Mostly, dendrochronologically dated wood is used for that. The calibration curves used for thecorrection of the radiocarbon ages are generated by plotting the wood radiocarbon ages versus the calibrated(cal.) ages. After a description of dendrochronology and a short overview over its history, the history ofits application for calibration of radiocarbon ages will be given. The “spectrum” of the variations will beexplained as well as the impact calibration had on archaeology.

5

Dendrochronology, or tree ring dating, is still the most precise dating method for archaeology. When thereis a sufficient number of rings (100-150 for oak) and the bark ring is preserved, a dating precision of 0.5 to 1year can be achieved. With preserved sapwood, the precision becomes 5-30 years, but when only heartwoodis preserved, dendrochronology gives a terminus post quem for the felling of the tree. Dendrochronologywas the only scientific method of precise dating until radiocarbon dating was invented. The first successfulattempts of dendrochronological dating were made by A. E. Douglass in 1906. In 1953, conifers in the WhiteMountains of California were found that were older than 4000 years, so that Edmund Schulman, a co-workerof Douglass, was able to construct an unbroken 4600-year sequence. Since a 7104-year tree-ring record waspresented by C. W. Ferguson in 1969, dendrochronology became important not only for dating but also forexamining the long-term variations of atmospheric 14C and for geophysical research. In 1957, Hessel de Vriesbegan measuring dendrochronologically dated wood samples after natural variations of the atmospheric 14Clevel were reported by K. O. Munnich from German oak samples dated by Bruno Huber. The variations are inthe order of magnitude of about 120h (Sternberg 1992). J. C. Houtermans used methods of Fourier analysisin his above-mentioned work for calculating a spectrum of the variations. He suggested both an approx.200- and 2000-year period. Later research has supported these suggestions and added other frequencies, forexample a periodicity of 10,000 - 12,000 years, to the spectrum (Sternberg 1992). Although some of theshorter periods (11, 88, and 210 years) have been identified with solar activity (Damon and Jirikowic 1992),the radiocarbon spectrum “is by no means fully understood” (Sonett 1992). The variations are so hard tounderstand because there are many possible sources interacting. They influence either the production of 14Cin the atmosphere or cause changes in the carbon/radiocarbon geochemical system (Sternberg 1992):

Radiocarbon is produced when neutrons produced by cosmic rays interact with 14N in the atmo-sphere; thus, it is affected by the galactic primary cosmic-ray flux, modulation of this flux by theheliomagnetic field and by the geomagnetic field, or by production due to solar cosmic rays. Sys-tematic changes include changes in geochemical reservoir sizes or exchange rates between them,or in the amount of 14C in the reservoir or system as a whole.

Unfortunately, the variations in the radiocarbon production are not reflected unaltered in the radiocarboncontent of tree rings: “14C studies require the consideration of complex transport processes damping outfast processes and shifting the phase” (Kocharov 1992).

The introduction of calibration had such a big impact on dating that it is called “the second radiocarbonrevolution”. “The second radiocarbon revolution involved the re-interpretation of European prehistoryfollowing the introduction of calibration curves, when events in Europe were found to be earlier than (notjust uncomfortably close to) their supposed progenitors in the Near East” (Tuniz, Zoppi, and Barbetti 2003).On the basis of “conventional” 14C dates it had previously been assumed that European prehistoric culturesgenerally postdate Middle East cultures (Becker 1992).

It has to be paid attention that calibration is applied in the right way, appropriate to the event beingdated. When dating one event by dating many samples associated with that event, the samples have to becalibrated together. When the samples are calibrated individually, the age distribution for the event becomesbroad, and it becomes the broader the more samples are measured (Ottaway 1986).

1.2 Accelerator mass spectrometry (AMS)

We have witnessed two revolutions so far: The first radiocarbon revolution was the introduction of radiocar-bon dating. The second radiocarbon revolution was the introduction of calibration and the re-interpretationof datings. There is a third event which is called a “radiocarbon revolution”: the introduction of acceleratormass spectrometry. For understanding why this is a revolution, we have to remember that radiocarbonin the first decades was done via decay counting (see section 1.1.1). Only the 14C atoms decaying duringthe measurement period could be detected. The sample masses required for this technique were about 1 gcarbon. Although 1 g of carbon already is a small amount, not all types of samples could be dated. Thecarbon yield of different sample materials differs a lot, so that in some cases far more than only few grams

6

of original sample were needed. Very small samples could thus not be dated, and some other samples aretoo valuable for allowing the removal of for example 100 g sample material.

In a modern sample, the average fraction of 14C decaying per day equals only 3.3 ∗ 10−7 of the amountpresent. If the number of 14C atoms present could be counted instead of only the number of decaying ones,the sample size could be reduced drastically. This is exactly what accelerator mass spectrometry does. Itis in principle a very easy technique: The carbon atoms are extracted as ions from the sample, they areaccelerated, separated from each other, and counted. The separation and counting of isotopes of differentmasses is called mass spectrometry. This is where the name accelerator mass spectrometry comes from: itis a mass spectrometric measurement with the help of an accelerator. The accelerator is needed to producehigh enough ion energies to make a separation of different ions with almost equal masses possible.

First of all, we will follow a 14C atom on its way from the sample to the final detector for showing howAMS works in principle. Background levels and precision of AMS will be addressed after that. The impactof AMS on archaeology and its advantages over decay-counting will be explained thereafter. A short historyof AMS will end this section. A lot of the information presented here can be found in Gove (1992).

From sample to detector

All laboratories have their specific design of an AMS setup. I will try to explain the principles as general aspossible, but when more details are needed, I will refer to the setup that is installed at the 14C AMS datinglaboratory at Aarhus University. In summary, the carbon ions are extracted from the sample, acceleratedwith 0.5-10 MV, separated according to their momentum, charge and energy and finally counted by an iondetector after identification by nuclear mass and charge. Accelerator mass spectrometry must be able toseparate nuclides of almost equal mass, sort out interfering molecules and measure the abundances of ionsin different orders of magnitude.

The sample is placed into the ion source in the form of elemental carbon, i.e. graphite. A beam of caesiumatoms is targeted at the sample which causes negative carbon ions to leave the sample surface. They areaccelerated towards a positive electrical potential. The most important mass-14 component that disturbsthe 14C measurement is already removed: 14N does not form negative ions and is therefore not present inthe ion beam.

When the ions are formed, they have different energies. The ion energy is the sum of the energy theyobtained from the acceleration towards the positive potential, which is equal for all of them, plus the kineticenergy they obtained from the ionization. Only ions with the right energy are desired to enter the accelerator.The ion beam is therefore electrostatically deflected. Only ions with the desired energy E are moving on thetrajectory of radius r:

εr =Mv2

Q∝ E

Q(1.3)

with M = nuclear mass, Q = charge, v = velocity and E = energy of the ion and ε = electric field. Thekinetic energy of an ion is E = 1

2mv2.We have thus obtained a beam of ions with equal energy. Ions with mass 12, 13 and 14 are now selected

for sequential or simultaneous injection into the accelerator. The so-called injection magnet selects the ionswith the desired mass. In a magnetic field, ions are deflected according to equation 1.4.

ME

Q2∝ (Br)2 (1.4)

with B = magnetic field. Only ions with a specific MEQ2 are deflected to the circular path with radius r. As all

ions have the same charge (-1 from the ion source) and as the above-mentioned electrostatical filter selectedions with equal energy, one can also say, “Only ions with a specific mass are deflected to the circular pathwith radius r”. With varying the magnetic field intensity B, one can now chose between the ions with mass12, 13, or 14. As this magnet is used for injecting beams of ions of different masses, it is called injectionmagnet. Many AMS laboratories cannot accelerate the large 12C− currents and only inject mass 13 and

7

Figure 1.3: A negative ion beam enters the tandem accelerator, loses electrons in the stripper material andleaves the accelerator with a charge of 3+.

14. The mass-14 beam consists mainly of 12CH−2 and 13CH−. 14C is present in this mass-14 beam, but its

percentage is negligible as the other carbon isotopes are far more abundant.The ion beam enters now the accelerator. Tandem accelerators are used in this case. The negative

ion is attracted by a positive potential in the middle of the accelerator. Typical acceleration voltages are2MV for Tandetrons and 6MV for Van de Graaff accelerators. In the middle of the accelerator, a so-calledstripper material is installed. Collisions with the stripper material, gas or foil, remove several electrons, sothat the resulting carbon ions are positively charged. +3 is the most common case for 2MV accelerationand +4 for 6MV. Figure 1.3 shows a sketch of the tandem accelerator. When losing 3 or more electrons,molecules are not longer stable. 12CH−

2 and 13CH−, for example, are removed from the mass-14 beam. Thestripper removes thus the interfering molecules. After the accelerator, another magnetical analysis (afterequation 1.4) is necessary: Charge Q and energy E of the ions is different due to the electron stripping andacceleration. Also the mass M of some constituents of the ion beam can be different, as molecules weredestroyed.

Velocity selectors or Wien filters consist of magnetic and electric fields at right angles to each other andperpendicular to the direction of the incident ions so that only ions with a specific velocity are not displaced:

v2 = 2EM

Q2∝ ε2B2 (1.5)

Afterwords, the ions have to be counted. More abundant isotopes can be counted in faraday cups. Theseare devices that just measure the charge that accumulates on them. Less abundant ions are counted withparticle detectors. These have an additional advantage: The rate of the energy loss dE/dx identifies thenuclear charge Z:

dE

dx∝ Z2

v2(1.6)

The identification of the nuclear charge is only possible when the abundances of the different ions are limited.When plotting the count ratio of a particle detector, a picture similar to figure 1.4 emerges. The final energyis the total energy minus the energy loss. One would expect that only 14C enters the particle detector sothat only a 14C peak could be observed. This is not the case because ambiquities can occur. It is for examplepossible that particles that are removed from the ion beam again enter the beam after small-angle scatteringon residual gas particles (i.e. on gas particles that are not removed although the system is evacuated). Infigure 1.5, the whole procedure for the mass-14 beam is summarized.

Precision and background

High-quality AMS measurements can reach a precision in pmC determination of about 0.2 to 0.3%. Theaccelerator background, that is the amount of 14C atoms that are registered although the sample is 14C

8

Figure 1.4: Count ratios of 14N, 12C, 13C and 14C in a particle detector as a function of total energy andfinal energy.

Figure 1.5: Following the mass-14 beam through the AMS measurement procedure

9

free, can go down to a 14C level according to 60-70,000 years. Dating is normally limited by the chemicalpreparation background to 50,000 years but can be better with special techniques (Tuniz, Zoppi, and Barbetti2003). There are different background sources in different steps of the sample preparation and measurementprocess after Kirner, Taylor, and Southon (1995):

1. Machine background: 14C detected when the sample is 14C-free

(a) Detector anomaly: 14C pulse registered when no 14C ion is present

(b) Ion identification anomaly: particle of same mass/energy ratio as 14C reaches the detector

(c) Beam-line contamination

2. Combustion/acidification background

(a) Materials contamination from materials in the combustion/acidification tube

(b) Tube contamination

3. Graphitisation background

(a) Materials contamination (e.g. catalyst)

(b) Reaction tube contamination

4. Pseudo 14C-“dead” sample background

(a) Sample erroneously assumed to contain no 14C

(b) 14C introduced into material that contains no 14C

Detector anomalies, or electronic noise, can be measured by collecting a spectrum for several days withoutinjecting any particles into the accelerator (Beukens 1992). Charge recombination in the detector createsa tail from the 12C and 13C peaks which underlies the 14C peak. Nuclear physics techniques of spectrumanalysis can be used to cope with this problem of a “tail”, but the reduced statistical precision limits thebackground level (Beukens 1992).

The ion source can also introduce contamination, because only about 10% of the sample’s carbon atomsis turned into negative ions and the remaining 14C atoms are deposited somewhere in the ion-source re-gion (Beukens 1992).

Kirner, Taylor, and Southon (1995) also observed that the way of sample storing has an effect on thebackground value. A geologic graphite sample that was powdered and encapsulated under argon had a 14Cage of 69,000 BP while samples of the same material that were powdered and encapsulated in air had ages of58-60,000 BP. The materials contamination from graphitisation could for example been estimated by pressingpure catalyst into a target and then measuring it in the accelerator. The disadvantage of this method isthat the ion beam current in this case is too small and instable for a general statement (Vandeputte, Moens,Dams, and van der Plicht 1998).

Impact on archaeology and advantages over decay-counting

The most important background in decay counting, the cosmic radiation, is thus eliminated in AMS. It wasanticipated in the beginning of AMS that the background reduction could make the dating of samples upto 100,000 years old possible. This is not the case, though, because contamination-free samples can not beprepared (Kirner, Taylor, and Southon 1995). The introduction of AMS reduced the required sample masseswith a factor of approx. 1/1000 and is therefore sometimes called the “third radiocarbon revolution” (Tuniz,Zoppi, and Barbetti 2003). Samples that before were too small or too valuable could now be dated. It is nowfor example possible to select only the best samples from a skeleton, “minimizing problems with degradationand contamination”. When a bone is reasonably preserved, 14C dating and stable isotope analysis is possiblewithout destroying the object (Arneborg, Heinemeier, Lynnerup, Nielsen, Rud, and Sveinbjornsdottir 1999).

10

Only the “capital costs and the greater complexity of AMS hardware” (Gove 1992) have so far preventedAMS from completely supplanting decay-counting facilities, although the number of AMS laboratories is stillincreasing.

The development of AMS had a strong impact on archaeology, alone by the reduction of required samplemass to 1/1000 (Harris, Grove, and Damon 1987). A reduction of sample mass in conventional measurements,the use of small-counter facilities, had the disadvantage of long measurement times: several days for onesample. AMS with measurement times about half an hour to a few hours per sample is thus much moreeffective. The small required sample mass makes it possible to date objects that were too small or toovaluable to be dated with the conventional method. Especially when dating the introduction of agriculturein different areas, AMS is the only possible dating method that can directly date the key material, singlecereal grains. Those plant remains are too small to be dated conventionally and too mobile to be datedstratigraphically or via associated finds (Harris, Grove, and Damon 1987).

The advantages of using an accelerator for 14C mass spectronomy are the following:

• no interference with 14N because it does not form negative ions• the samples are smaller and more easily prepared than for decay counting• it is possible to accelerate all 3 C isotopes, so in principal both the date from 14C/12C or 14C/13C as

well as additional information from 13C/12C is available

It is possible to measure other radionuclides beyond 14C with the accelerator. The advantage of AMS isthat it can detect long-lived cosmogenic radioisotopes in the presence of vastly larger quantities of their stableisotopes. Many radionuclides which are produced in measurable amounts in the atmosphere or environmenthave decay constants “matching temporal scales relevant to the history of hominidae” (Tuniz, Zoppi, andBarbetti 2003). While 14C can reach 50,000 years ago, when Homo sapiens sapiens started colonizing vastregions of our planet, can 10Be and others reach back to 5 million years when Australopithecus appeared. Thedifferent detectable radioisotopes can not only be used for dating. A plenitude of applications in hydrology,geoscience, materials science, biomedicine, sedimentology, environmental sciences and many other fieldsemerged as soon as the AMS detection capabilities of the appropriate isotopes were demonstrated. Oneexample is the measurement of water flow rates with the 36Cl bomb pulse: 36Cl was produced in nuclearweapon tests in the 1950s by neutrons interacting with the chlorine in the seawater. It was injected into thebiosphere at a level which was two orders of magnitude above the pre- and postbomb test ambient levels.

History of AMS

In 1977, two independent approaches using particle accelerators were taken, one with a cyclotron and one witha tandem Van de Graaff electrostatic accelerator. In May 1977, 14C in an organic sample, barbecue charcoal,was measured via AMS for the first time. The team at the University of Rochester (USA) demonstratedthat negative 14N ions are unstable (Gove 1992). Thus, the most important disturbing factor in 14C massspectronomy, the 14N isotope with nearly the same mass, could be eliminated. NH− molecular ions are theonly nitrogen species left after the negative ion source (Beukens 1992). Only three weeks later after thissuccess, another group from the Canadian Simon Fraser University detected 14C in a AD 1880-90 woodsample at McMaster University’s accelerator, also in Canada. Purportedly, neither the Rochester nor SimonFraser group was aware of the other group’s efforts at that time. It could be said that the time was justripe for the development of AMS, after the first accelerator mass spectrometric detections of 3He alreadytook place in 1939 and the tandem accelerator employing negative ions had been invented by Luis Alvarezin 1951 (Gove 1992). Anyway, is took some time until a tandem accelerator was used for 14C dating. Itwas shown in 1977 that if three or more electrons are removed from a neutral mass 14 molecule like 12CH2,the molecule dissociates in a Coulomb explosion and the resultant fragments are swept aside before reachingthe final detector. Thus, another source of interferences with 14C could be eliminated. For these firstattempts of AMS radiocarbon dating, existing accelerators were used, but later small tandem acceleratorswere specifically designed for AMS, because the high terminal voltages of the big accelerators were notnecessary. At the end of the 1970s, 14C was measured with completely acceptable sensitivity using smalltandem accelerators with terminal voltages around 2 MV, because all that was required was a negative ion

11

energy high enough to have a reasonable probability of producing charge 3+ ions in the terminal stripper toensure the elimination of mass 14 molecules. The first AMS 14C datings were made in 1978.

1.2.1 Reporting of 14C data

Stuiver and Polach (1977) developed guidelines for the reporting of 14C data that still are in use. Thefollowing remarks about calculating and reporting of 14C data can be found in their article. To find outwhich measured 14C activity or concentration belongs to which age, standard materials of known age haveto be measured. To ensure that results from different laboratories are comparable, all should use the samestandard material. Now, all laboratories report their data either directly related to NBS [Natural Bureau ofStandards] oxalic acid or indirectly by using a substandard which is directly related to the NBS oxalic acid.The internationally accepted radiocarbon dating reference value is 95% of the activity in 1950 AD of the NBSoxalic acid normalized to δ13C=-19h PDB (see section 1.3.1 for an explanation of 13C fractionation and theδ-notation). The activity of this standard does not change, because it is the activity measured in a certainyear (1950 AD), although the activity of oxalic acid is changing with time. It is called “absolute internationalstandard activity”, AISA. Most laboratories use the activity AON , which is 95% of the measured net oxalicacid activity / count rate:

AON = 0.95AOX(1− 2(19 + δ13C)1000

). (1.7)

The expression in brackets accounts for fractionation. The factor 2 considers that fractionation for 14C isabout twice the fractionation for 13C. As AON depends on the year of measurement, y, it has to be correctedfor decay between 1950 AD and the year y of actual counting date. The absolute international standardactivity AISA is thus

Aabs = AONeλ(y−1950) (1.8)

with λ = 18267years−1. λ is based on the 5730 years half-life. Terrestrial samples are normalized to δ13C =

-25h VPDB, the postulated main value of terrestrial wood:

ASN = AS(1− 2(25 + δ13C)1000

) which is an approximation of the more precise ASN =AS0.9752

(1 + δ13C1000 )2

. (1.9)

For the calculation of the radiometric age of a sample, the assumption is made that the atmospheric 14Clevel was constant in all past times and that is by definition equal to Aabs after normalizing to -25h. Theage t of a sample it thus

t = −8033 lnASN (1950)AON (1950)

with a half-life of 5568 years and thus a mean life of 8033 years. (1.10)

t is independent from the year of measurement, because both sample and oxalic acid lose their 14C at thesame rate. The years calculated with this formula are called conventional radiocarbon ages in years BP(before present) with present = 1950 AD.

Another method of giving radiocarbon values is “percent modern carbon”, pmC:

pmC =ASN

Aabs100% =

ASN

AONeλ(y−1950)100%. (1.11)

Here is y the year of oxalic measurement and λ = 18267a−1 is based on the 5730 a half-life. The pmC

is sometimes defined differently, as ASN

AON100% without the factor correcting for decay since the year of

measurement. For archaeological samples, there is almost no difference between the two definitions of pmC,as the time since measurement is negligible compared to the age of the sample. However, when reporting forexample biomedical samples, it should clearly be stated if the correction for decay since measurement hasbeen applied or not.

12

The relation between the conventional radiocarbon age t and “absolute” percent modern carbon pmC is

t +y − 1950

1.03= −8033 ln

pmC100

(1.12)

The above calculations belong to measurements of the 14C/12C ratio. With accelerator mass spectrometry(see section 1.2), the 14C/13C ratio is measured, and some of the equations have to be adjusted to that fact.In equation 1.7 for example, the factor 2 is not longer necessary if the 14C/13C ratio is measured. The factorwas only introduced in that equation to account for the fact that fractionation between 14C and 12C is abouttwice the fractionation between 13C and 12C. We can assume that the fractionation between 14C and 13C isapproximately the same as between 13C and 12C. In equation 1.9, the factor 2 of the approximated expressioncan be left out because of the same reason. This means that in the exact expression in equation 1.9 thefactor (1 + δ13C

1000 ) not longer has to be inserted quadratically. This means that the measurement error inδ13C determination only has half the influence on a date that is obtained measuring the 14C/13C ratio. Ifthe error in the δ13C value for example is 1%, then the age error will be 160 years if the measurements arebased on 14C/12C ratios. The same δ13C error will only lead to an age error of 80 years if the measurement isbased on 14C/13C measurements. The usual precision of mass spectrometric measurements of δ13C is about0.1h. The squared δ13C ratio in the 14C/12C = ASN formula 1.9 leads to a factor 2 in the age error as thelogarithm of a squared value is twice the logarithm of that value. The age is calculated using the logarithmof the ratio, see equation 1.10.

The 14C/12C ratio of a sample can be expressed in the following way:

(1412

)S = (1413

)S ∗ (1312

)S = (1413

)S ∗ (1312

)V PDB ∗ (1 +δ13CS

1000). (1.13)

The same is true for the 14C/12C ratio of the oxalic acid standard. The pmC of a sample after 14C/13Cmeasurement is thus expressed as

pmC =1

0.9558∗ (

( 1413 )S

( 1413 )Ox

) ∗ (1− 25

1000

1 + δ13CS

1000

) (1.14)

1.2.2 Reservoir Effects

The above explained principles of radiocarbon dating only work when the samples obtain their carbonfrom the well-mixed atmospheric carbon reservoir or other parts of the earth which are in balance with theatmosphere. Otherwise is it not possible to estimate precisely the initial 14C concentration in an unknownsample with the measurement of a limited number of modern materials (Broecker and Walton 1959). Interrestrial material, depletion or enrichment in 14C is only due to isotopic fractionation. In material ofdifferent origin, 14C depletion can be caused by the long residence time carbon has in the reservoir thesample comes from. Carbon is in the following way distributed to different reservoirs: the oceans, storing93% of the total carbon, the biosphere (5%), and the atmosphere (2%). The atmosphere is thus the smallestglobal carbon reservoir. The average atmospheric CO2 concentration is 360 ppmv and its partial pressure is10−5.5. The δ13C value of the atmosphere was originally around -6.4h but is now decreasing due to burningof fossil fuels (Clark and Fritz 1997). In the case of a reservoir with a different radiocarbon content thanthe atmosphere, corrections of the initial radiocarbon content or activity have to be applied. Otherwise,spurious ages would be obtained. The effect the 14C content of a certain reservoir has on the 14C age of asample is called reservoir effect.

There are different types of reservoirs which cause problems in radiocarbon dating. One is the oceans,leading to the marine reservoir effect, the other is freshwater with considerable amounts of 14C depletedcarbon, leading to the freshwater reservoir effect. A lower 14C activity can also be expected in the neigh-bourhood of fumaroles where old CO2 is released (Olsson 1976b).

The marine reservoir effect is a well-known and broadly accepted phenomenon. Water that wells up fromthe deep parts of the ocean has long been cut off from the atmospheric carbon cycle and contains therefore

13

old CO2 with a low 14C content: The ocean can be divided into two parts, the surface water and the deepwater. Both are well mixed individually, and there is little exchange between them. In ocean water, theδ13C value of dissolved inorganic carbon is 1h, so that there is a difference of 26h between the atmospherewith δ13C = -25h and the ocean (fractionation and the δ-notation will be explained in section 1.3.1). Adifference in the 13C/12C ratio of 26h means a difference of approximately 52h or 5.2% in 14C/12C, so thatthe ocean, compared to the atmosphere, should have a 14C activity of 105.2% (Lanting and Van der Plicht1996). Rapid exchange with the atmosphere, though, only takes place in the surface water, so that theseconsiderations do not apply to the deep ocean. There is 102 times as much deep water as surface water. Inaverage, the proportion of carbon that circulates down into the deep water is about 102 times as great asthat which rises up. The 14C in the deep water has more time to decay and thus the activity of deep wateris less than the activity of surface water (Olsson 1976b). Via photosynthesis, plants incorporate the carbonfrom this CO2. From the phytoplankton via the zooplankton and fish, this “old” carbon finally also endsin food for animals living on land. One example are recent polar bears from Svalbard and East Greenlandwho had 14C ages of 480±70 and 495±45 years, respectively. The same effect can be found in humans - “aperson who eats much fish will naturally have lower 14C activity than a person who eats mainly terrestrialfood” (Olsson 1976b). This effect perhaps is conserved as a charred residue in a cooking pot, when the fishhad been cooked. The radiocarbon age of this food residue now is older than its actual age.

Corrections of the marine reservoir effect are made by subtracting the reservoir age of the ocean fromthe measured radiocarbon age of the sample. The reservoir age is about 400 years for the North Alanticaccording to measurements and model calculations; see Stuiver, Pearson, Branziunas (1986). Reservoir agesof different parts of the oceans can vary strongly depending on sea currents and local seabed/coast shape.The age differences between surface ocean and atmosphere are generally greater at high latitudes than inthe tropics (Gillespie and Polach 1976). For finding out if a sample has marine origins that necessitatereservoir corrections, the content of the stable carbon isotope 13C is measured. 13C values differ significantlyfor organic material of marine and terrestrial origin. When 14C dating human bones, the percentage ofmarine food has to be estimated for calculating a marine reservoir correction. One example is the stableisotope analysis and 14C dating of Greenland vikings. The endpoint for a 100% terrestrial diet of δ13C =-21h is easy to find as there are many populations who solely live on terrestrial products. The endpoint fora 100% marine diet is harder to find because no human population a priori can be expected to have a 100%marine diet (Arneborg, Heinemeier, Lynnerup, Nielsen, Rud, and Sveinbjornsdottir 1999). Therefore, theδ13C value of -12.5h of the most marine individuals that the authors were aware of, Thule culture Eskimos,was used. The δ13C value of the viking bones is an indicator of the percentage of marine food and thus ofthe extent of reservoir correction that has to be applied. When correcting the 14C dates in this way, theages of the human bones fit well historically assumed ages and the ages of associated terrestrial material liketextiles. In this case, a simple linear mixing model could be applied as the population on Greenland mainlylived on proteins from meat and dairy products because agriculture was not possible in the cold climate onGreenland (Arneborg, Heinemeier, Lynnerup, Nielsen, Rud, and Sveinbjornsdottir 1999).

There are different sources of 14C depleted carbon in freshwater environments. The most important is thedissolution of geologic carbonates, which because of their high age are almost 14C free. Other explanationsinclude inputs of old soil humus, residence time of for example ground water in an aquifer, or vital effectsof the species studied (Culleton 2006). Carbon can also be dissolved from rocks other than carbonates, forexample from vulcanic glasses. This accounts for example for high reservoir ages in Icelandic groundwatersalthough there are no carbonaceous rocks on Iceland. The effect of CO2 from the decomposition of vulcanicglasses can be corrected with measuring the boron concentration in the water, as carbon and boron arereleased in stoichiometric relation from the glass (Sveinbjornsdottir, Heinemeier, and Arnorsson 1995). Inlakes with a large depth to surface ratio in combination with good wind protection, the CO2 exchange ratiobetween the atmosphere and the lake water is low and can also lead to a 14C depletion in the water (Hakansson1976).

If the 14C depletion of the freshwater system is caused by dissolved bicarbonates and carbonates, thefreshwater reservoir effect is also called hardwater effect. The water hardness is defined as the concentrationof the alkaline earth metal ions, predominantly calcium (Ca) and magnesium (Mg). They originate often

14

from carbonates. The water hardness is therefore an indicator of the carbonate concentration and thus ofthe amount of 14C-dead material in the water. Hard water can be found in regions where limestone andsandstone are dominating.

The effect of dissolved bicarbonates on the radiocarbon age has already been anticipated during the firstradiocarbon datings, when Godwin (1951) examined dates from British lake deposits:

Too great an age may result from introduction of inactive Carbon, as with bicarbonate derivedfrom ancient limestones, brought into a lake, where it is fixed in organic compounds or precipitatedthrough biological activities.

In 1954, Deevey et al. examined a hardwater lake and dated water samples as well as plant samples, alsofrom terrestrial plants. The water samples had an apparent age of 2200 years, and also the clams and plantsfrom the lake which use bicarbonate as a carbon source had comparable ages. Deevey, Gross, Hutchinson,and Kraybill (1954) conclude: “Great care must be clearly be exercised in the future when material fromhighly calcareous regions is being examined”.

In 2006, B. J. Culleton measured paired samples of charcoal and shells from lake sites in Californiaand found a 340 years discrepancy between them as well as a greater variability of ages among the shellsthan among the charcoal. This might be an evidence for genus-specific reservoir corrections, maybe basedon habitat differences (Culleton 2006). A freshwater reservoir effect also explains the difference betweenarchaeological and radiocarbon-based chronology for the Catacomb cultures of the North-West Caspiansteppe (Shishlina, Van der Plicht, Hedges, Zazovskaya, Sevastyanov, and Chichagova 2007). Seeds andfishbones that were found in the same grave had an age difference of 640±60 14C-years, and the δ15N valuesof human bone indicated that aquatic protein accounted for 70% of the total protein supply so that a reservoircorrection of about 400 years has to be made for the human bone radiocarbon dates. More examples for thefreshwater reservoir effect in archaeological material will be given in section 1.2.4.

The occurence of the hardwater effect on food crusts on pottery was first proposed in 2003 (Fischer andHeinemeier 2003). The results of Fischer and Heinemeier (2003) have been doubted, though. Apparently, thenumber of dated samples was small enough to explain the age difference between terrestrial and freshwatersamples with statistical methods so that the hardwater effect was not necessary as an explanation. Insteadof a real radiocarbon age difference, Hart and Lovis (2007) explain the measured values with a single outlierand statistical variations. The basics of the hardwater effect will be explained in section 1.2.3.

In coastal areas as for example the Danish fjords, a mixing of two carbon reservoirs can be observed:the marine and the freshwater reservoir. Danish Baltic Sea areas like the Skagerrak-Kattegat and the Beltsshow the same reservoir age as the North Sea and North Atlantic: about 400 a (see a description of themarine reservoir effect above). In contrast to that, the Danish fjords have higher and more scattered agesbetween 400 and 900 years and are thus not part of the uniform marine reservoir. The variability in thereservoir ages of the fjords can best be explained with different concentrations of old dissolved carbonate inthe soil (Heier-Nielsen, Heinemeier, Nielsen, and Rud 1995).

1.2.3 How the hardwater effect works

The mechanisms leading to the hardwater are explained in Clark and Fritz (1997) and Fontes and Garnier(1979) where a lot of the information presented here can be found. Normally, there is no reason for datingriver water, because its age is known as modern. It is only used for estimating the hardwater effect thatinfluences the age of freshwater organisms. Most research in order to understand the mechanisms thatproduce the high water ages has therefore been done in the area of groundwater dating. Groundwaterdating is an important part of water resources management. For human use over a long period of time, onlygroundwaters that are recharged constantly provide sustainable solutions. “Using groundwaters that are notactively recharged is mining” (Clark and Fritz 1997), because the groundwater reservoir will be exhaustedafter a certain period of water extraction. Dating the water is a method to decide whether a groundwaterreservoir is actively recharged or not.

The hardwater effect makes it complicated to date groundwaters because the disolved carbonate makesthe initial activity of the water smaller than 100 pmC. pmC is the abbreviation for “percent modern carbon”

15

and is a measure of 14C activity. 100 pmC is the activity of the atmospheric carbon before the beginning ofthe bomb tests. For estimating the correct initial 14C activity, model calculations had to be done and themechanisms of solution and transport of the different carbonaceous species had to be understood. Ground-water dating is therefore an important field of study also regarding the hardwater effect in other freshwatersystems. The measurement of the tritium content of a groundwater is a possibility for deciding if the wateris affected by the hardwater effect. The half-life of tritium is only 12.26 years so that tritium-containinggroundwater must be “post-bomb”, i.e. relatively young water. A hardwater effect in groundwater has forexample been reported by Boaretto, Thorling, Sveinbjornsdottir, Yechieli, and Heinemeier (1998) from Hvin-ningdal in Denmark. Tritium values showed that the water was “post-bomb water”, but its 14C content was30 to 100 pmC.

There are two sources of dissolved carbon in groundwaters and so two sources for an explanation ofhigh 14C ages in young water: relatively active carbon comes from the soil zone and less active carbon is ofinorganic origin. The carbon of inorganic origin is itself a mixture of active carbon from soil gas CO2 andold carbon from carbonate in the subsurface. It is also called DIC, as an abbreviation for dissolved inorganiccarbon. This will be described first. Later, I will explain the effect of DOC, which means dissolved organiccarbon. DOC and DIC 14C values can differ significantly in groundwater, with DOC in most cases beingyounger, but are often in the same order of magnitude (Long, Murphy, Davis, and Kalin 1992). DOC canin single cases also lead to a spurious, too young radiocarbon age of the water, when young DOC entersold water. Carbon transformations are linked through acid-base and redox reactions which are most oftenmediated by bacteria (St-Jean 2003). Bacteria act as catalysts and can in these cases influence isotopic ratiosbecause they prefer to break the looser molecular bonds. The hardwater effect is expected to be greaterin running, i.e. river water, than in stagnant water like lake water. If there is not a noticeable meltwatercomponent, river water consists largely of groundwater (Lanting and Van der Plicht 1996). This is anotherreason why groundwater research methods are being discussed here. The definition of DIC comprises fourspecies:

• Carbon dioxide CO2

• Carbonic acid H2CO3

• Bicarbonate anion or hydrogencarbonate HCO−3

• Carbonate anion CO2−3

The first two species, CO2 and carbonic acid, are often summed up as CO2 because the carbonic acid onlyexists in aqueous solution. The bicarbonate anion HCO−

3 is an amphoteric substance. That means, it canboth act as acid and base because it both can donate and accept protons. Bicarbonate is the conjugate baseof carbonic acid H2CO3 and the conjugate acid of the carbonate ion CO2−

3 :

CO2−3 + 2H2O ↔ HCO−

3 + H2O + OH− ↔ H2CO3 + 2OH−

H2CO3 + 2H2O ↔ HCO−3 + H3O+ + H2O ↔ CO2−

3 + 2H3O+ (1.15)

The concentration of HCO−3 and CO2−

3 together is called carbonate alkalinity. Alkalinity denotes the con-centration of dissolved species which act as proton acceptors and buffer pH, i.e. consume acidity.

In the soil, root respiration and the decay of organic material release CO2. In contact with water, asmall amount of this CO2 forms carbonic acid (H2CO3) which can dissolve lime from the surrounding rock.The dissolved lime hardly contains any 14C because of the high age of the lime stone. Carbonic acid is thepredominant acid in natural waters and most responsible for rock weathering (Langmuir 1997). Water plantsconvert CO2 and water to glucose and oxygen and use the glucose as an energy source and a basic materialfor other organic matter. When an extensive amount of the CO2 in the water has a high age, then the plantwill accordingly show a spurious, high radiocarbon age. Correspondingly, fish that feed on these plants andhumans that eat these fish, will also show too old radiocarbon ages. This effect could also be transferred tothe food crusts on pottery in which a considerable amount of aquatic food was cooked. This freshwater partof the carbon cycle will be examined more detailed below.

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Figure 1.6: The pathway and associated fractionation of 14C and 13C in CO2 during photosynthesis, respi-ration in soils, and dissolution by groundwaters (Clark and Fritz 1997).

17

Fresh groundwater originates exclusively from precipitation, which in most cases percolates through soiland geosphere. The CO2 in the root zone, which is dissolved by rainwater, has a “recent” 14C activityand its δ13C is approximately -25h. The amount of CO2 that can dissolve depends on temperature, initialwater pH and the partial pressure of CO2. Although rainwater contains some CO2 from the atmopshere,the groundwater’s radiocarbon signal is dominated by the carbon from the soil zone. In the deeper subsoilexchange takes place between this dissolved CO2 and fossil marine carbonate (e.g. limestone) which hasno 14C activity and δ13C = +1h (see above). When finally equilibrium is reached, CO2 in groundwaterhas only half the “recent” 14C activity and its δ13C is c. -12h (Lanting and Van der Plicht 1996). Otherprocesses like the dissolution of extra CO2 and exchange processes in the unsaturated zone can alter the14C and 13C concentrations additionally. To correct the measured 14C concentration, the δ13C value of thewater can be measured. If assuming that fossil carbonate has a δ13C value of about 0h and CO2 from theroot zone has -25h, the corrected 14C activity of the water is

Ad = Am−25

δ13Cm(1.16)

with the measured activity Am. The activity Ad has now to be taken to calculate the age, as the uncorrectedmeasured activity Am would overestimate the age (Boaretto, Thorling, Sveinbjornsdottir, Yechieli, andHeinemeier 1998). The 14C age measurement can also be corrected by estimating the initial 14C activiy Ain

that originates from the dilution of the atmospheric activity Aatm with fossil carbonate:

Ain = Aatmδ13Cm

−25(1.17)

Boaretto, Thorling, Sveinbjornsdottir, Yechieli, and Heinemeier (1998) discovered that Am is correlatedwith the oxygen concentration of the water. One can therefore assume that besides the dissolution ofcarbonates, the oxidation of old organic carbon in the soil dilutes the 14C concentration, as will be explainedbelow when discussing DOC.

The existence of a three phase system consisting of gaseous CO2 and aqueous and solid carbon al-lows significant isotopic exchange. Isotopic exchange is for example represented by the following reaction:14CO2+H12CO−

3 ↔12CO2+H14CO−3 . This process is responsible for 14C contents significantly higher than

those indicated by the single dissolution process in modern groundwater. It is known since Munnich’s re-search in 1957 (Fontes 1992). Each stage of the series of chemical reactions is isotope fractionating: whenCO2 gets dissolved in water, when it forms carbonic and bicarbonic acid and when the CO2−

3 forms solidcarbonate. Furthermore, each single compound will exchange with the other coexisting carbon species. How-ever, because of differences in reaction rates and large variations in the relative amounts of coexisting carbonspecies, isotopic exchange reactions may not reach equilibrium for each compound.

The inorganic carbon is mainly controlled by acid-base reactions. The distribution of the three speciesof dissolved inorganic carbon, CO2 (dissolved CO2), HCO−

3 (bicarbonate ion) and CO23− (carbonate ion),

is largely a function of pH (St-Jean 2003). The three DIC species are related in the following pH controlledchemical equilibrium:

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO−3 ↔ 2H+ + CO2−

3 (1.18)

The most important component of inorganic carbon in natural waters is bicarbonate. It is produced inthe reaction CO2 + H2O + MeCO3 ↔ Me(HCO3)2 with Me = Ca2+, Mg2+ or 2Na+. Dissolved CO2 orcarbonate, depending on the pH, generally accompanies bicarbonate in the unsaturated zone and in theaquifer. The higher the CO2 concentration is in the soil atmosphere, the lower is the initial pH. The lowpH is then buffered by mineral weathering in soil and upper bedrock. The most common and most effectivebuffering reaction is calcite dissolution with Me = Ca2+ in the reaction above. Carbonate dissolution is oftenautomatically considered as an index of 14C dilution and reported as “hardwater effect”. But single examplesshow exceptions from this general rule (Fontes 1992) so that the measurement of the water hardness is notsufficient to trace the dilution of 14C content in the water.

Carbonate is not the only mineral that gets dissolved in natural waters; silicate is another importantcomponent. There is a major difference between carbonate and silicate dissolution regarding the 14C/12C

18

of DIC. For systems in contact with the atmosphere, each equivalent of Ca, Mg, Na, and K ions dissolvedfrom silicate minerals is accompanied by the addition of 1 mole of atmospheric CO2 (see equation 1.20).For carbonate, 1/2 mole of atmospheric CO2 is added to the system for each equivalent of Ca and Mgdissolved so that 1/2 of the total CO2 is 14C-free while the other half has atmospheric concentration (seeequation 1.19). In contrast to that, no 14C-free HCO−

3 is added in the case of silicate solution (Broecker andWalton 1959). The only change to the carbonate system is the increase in pH that is associated with silicatedissolution. This increase in pH shifts the distribution of DIC species to the HCO−

3 field. If this occursunder non-saturated conditions in an open system, additional CO2 will be dissolved from the soil zone. Inany case, the DIC from silicate weathering is derived solely from soil CO2 .

CaCO3 + H2O = Ca++ + HCO−3 + OH−

OH− + CO2 = HCO−3

∴ CaCO3 + H2O + CO2 = Ca++ + 2HCO−3

(1.19)

In the following example of silicate dissolution, the plagioclase feldspar anorthite CaAl2Si2O8 is dissolved.

CaAl2Si2O8 + H2O = Ca++ + 2OH− + Al2O3 + 2SiO2

2OH− + 2CO2 = 2HCO−3

∴ CaAl2Si2O8 + H2O + 2CO2 = Ca++ + 2HCO−3 + Al2O3 + 2SiO2

(1.20)

These reactions are based on the assumption that nearly all the dissolved CO2 in fresh-water bodies is inthe bicarbonate ion form (Broecker and Walton 1959). After the bicarbonate is formed, its 14C/12C ratio iscontrolled by the second factor, the exchange ratio of CO2 with the atmosphere. In igneous areas, silicatesolution is dominant so that the majority of dissolved bicarbonate has atmospheric origin. Rivers which areflowing over sedimentary rocks dissolve both silicate and carbonate minerals (Broecker and Walton 1959).

The 14C/12C ratio of the dissolved bicarbonate in fresh waters is thus controlled by

1. the ratio of the amount of carbonate to the amount of silicate dissolved2. the rate of exchange with CO2 in the atmospheric reservoir

CO2 exchange rates for rivers can be as high as 100 moles/m2, whereas CO2 exchange rates in inland lakesare about 5 moles/m2 (Broecker and Walton 1959).

Age distortion can also be introduced by dissolution of secondary calcite precipitated under open-systemconditions. Fractionation between dissolved HCO−

3 and solid calcite is probably very small. When calcitethat emerged from dissolved HCO−

3 is than dissolved again, it is hardly noticeable in the 13C content of theTDIC, and may lead to apparent aging of the TDIC (Fontes 1992). TDIC means total dissolved carbon.Thus the age of the DIC changes without changes in the 13C content that may indicate the age distortion.One example for this overestimation of 14C ages can be found in Aeschbach-Hertig, Stute, Clark, Reuter,and Schlosser (2002). 14C can further be diluted by sulphate reduction and methanogenesis, 2CH2O → CO2

+ CH4.CO2 produced from oxidation of organic matter most likely will alter the 14C activity of the DIC as

CO2 is one of the DIC species, no matter what its origin may be. A lower pH that is associated with thehigher concentrations of dissolved CO2 will additionally dissolve calcite if present and so further alter the14C activity in the DIC (Long, Murphy, Davis, and Kalin 1992). As Boaretto, Thorling, Sveinbjornsdottir,Yechieli, and Heinemeier (1998) noticed, is the 14C concentration of the water after correction for carbonatedissolution correlated to the oxygen content of the water. For estimating the extent of oxidation of old organicmatter in the soil, the highest measured oxygen concentration in the water body is taken as the initial oxygencontentration [O2]in. We assume that the missing oxygen was used for the oxidation of organic matter, Corg+ O2 = CO2. The fraction F of the total inorganic carbon in the water that was derived from the oxidationof organic matter is thus calculated to

F = 1.38[O2]in − [O2][CO2,total]

(1.21)

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where 1.38 is the ratio of the molecular weights. The 14C activity of the water when corrected for carbonatedissolution and organic carbon oxidation is thus

Acorr = Am−25

δ13Cm + 25F. (1.22)

The dissolved organic carbon DOC is the result of decomposition of higher organic matter, such asplants, in the soil. Its particle size is smaller than 0.45 µm. Organic carbon with particle sizes bigger than0.45 µm can also be present in groundwaters and is called “particulate organic carbon”. The DOC originatesfrom chemical and physical changes in soil organic matter (SOM) that becomes soluble (St-Jean 2003) andis stored in the soil waters. The concentration of DOC in soil moisture can reach a maximum of 10 to100mgC/L in the root zone. This concentration drops off towards the water table. Groundwaters oftenhave less than 1 to 2 mgC/L DOC, “although groundwaters in certain environments can recharge with muchhigher DOC concentrations” (Clark and Fritz 1997). DOC species comprise the so-called humic substancesthat are responsible for the dark colour of soils and some waters. Humic and fulvic acid are both humicsubstances and they are often the reason for contamination with younger carbon in archaeological samples.

DIC can be extracted from the water sample by acidifying it. The procedure used for my water sampleswill be described in detail in section 4.1.1. DOC can be extracted afterwards when the DIC is removed.One isolation technique for DOC is photo-oxidation, e.g. irradiating 2L of water with a 1200W UV-lampafter adding Na2S2O8 to expedite oxidation. In another isolation technique, water is passed through aseries of columns packed with pre-cleaned resin materials to collect DOC of different sizes (Long, Murphy,Davis, and Kalin 1992). In 10 to 120L filtered water, liquid chromatography separation of hydrophobicsubstances, fulvic and humic acids, is possible (St-Jean 2003). Whatever method is used, DOC analysis isregarded as difficult and time-consuming and requires large samples (St-Jean 2003). High molecular weightsubstances, for example humic acids, are insoluble below a pH of 2. They precipitate when DIC is removedby acidification, and that makes them more resistant to oxidation (St-Jean 2003).

When measuring the reservoir age of a water system, it has to be taken into account that the 14C contentof the water can be subject to seasonal or secular changes. The dating of one water sample only, taken ata special time, can therefore be not more than an estimate of the reservoir effect (Geyh, Schotterer, andGrosjean 1998). Lakes are subject for the biggest changes because in them there is no continuous flow ofwater. Bicarbonate for example is probably periodically concentrated in lakes by evaporation (Culleton2006). A very slowly running river or a lake can regain “recent activity” due to exchange with atmosphericCO2. The extent of the hardwater effect is for example dependent on the surface-to-volume-ratio of a lake. Itis thus basically dependent on the water depth, as the surface of a lake with outflow only changes minimallywhen the water depth decreases because of sedimentation (Geyh, Schotterer, and Grosjean 1998). Thereason for the dependence on the surface-to-volume-ratio is that exchange with the atmosphere only takesplace at the water surface while the dissolved inorganic carbon reservoir is proportional to the entire volume.When thus the water depth decreases because of a rising of the lake ground due to sedimentation, the watervolume gets smaller while the lake surface still is the same. There is thus the same exchange with CO2

from the atmosphere while the total amount of dissolved inorganic carbon decreases with the decreasingamount of water in the lake. Sedimentation in a lake is thus a reason for secular changes in the reservoirage. Sedimentation could also cut off the supply of groundwater to the lake so that the amount of dissolvedinorganic carbon decreases that is transported with the groundwater into the lake.

Temporal changes in the hardwater effect are due to water temperature and biological activity. In latesummer, lakes are often thermally stratified with warm water in the upper layers and colder water in thebottom of the lake. Towards winter, the upper layers cool down due to the sinking air temperatures untiltheir density exceeds that of the layers below, which are still a little bit warmer. Cool water from the upperlayers sinks thus down and the lake water gets mixed by this process. When water with different bicarbonateconcentrations gets mixed, an excess CO2 concentration builds up which increases during winter due to thedecomposition of organic matter. In spring, the upper water layers warm up and biological activity begins.Inorganic carbon precipitates due to the biological removal of CO2 and to a lesser extend due to degassing inthe warm summer. This takes place in the upper layers of the lake where there is enough light for intensivebiological activity. Carbonate that was precipitated through this process reaches the lake ground only when

20

the water in the bottom layers is supersaturated with CO2. Sedimentation takes thus mainly place at theend of the warmer season. Total dissolved inorganic carbon (TDIC) and precipitated carbonate should bein equilibrium, but as there can be more exchange with atmospheric CO2 the more carbon in the originalDIC reservoir is biologically removed, the 14C value increases with decreasing carbonate sedimentation rate(Geyh, Schotterer, and Grosjean 1998). The possible extent of the hardwater effect at the regarded sites onthe rivers Trave and Alster, respectively, will be described in section 3.2.1.

1.2.4 The hardwater effect in archaeological material

One example for the measurement of “too high” radiocarbon ages on human material is the Iron Gates region,at for example the sites Lepenski Vir, Vlasac and Schela Cladovei (Cook, Bonsall, Hedges, McSweeney,Boronean, Bartosiewicz, and Pettitt 2002). The measurement of human bone and associated charcoal orungulate bones showed an age difference of some hundred years. This difference, the reservoir age, comesfrom the consumption of fish from the Donau. As protein is the only source of nitrogen in human bones(see section 1.3.2), it is possible to reconstruct the percentages of riverine and terrestrial food that wereconsumed with measuring the δ15N value of the bones. The stable carbon isotope 13C is not so well suitedfor this purpose because the carbon in bones can originate not only from the consumed proteins, but alsocarbohydrates and lipids (Cook, Bonsall, Hedges, McSweeney, Boronean, Bartosiewicz, and Pettitt 2002).13C values reflect therefore not exclusively the meat consumption so that it is hard to differ between proteinsources from different reservoirs. In contrast to that, there is a linear relation between the δ15N value andthe proportion of freshwater, marine or terrestrial food. The relation between the δ15N value and the ageoffset, which is caused by the consumption of freshwater food, is therefore linear, too (Cook, Bonsall, Hedges,McSweeney, Boronean, Bartosiewicz, and Pettitt 2002). The δ15N value for the terrestrial diet end-memberis 8h, while δ15N for the aquatic resources end-member is 17h. A δ15N value of 15h that was foundfor some individuals indicates so a diet with 79% aquatic protein: 0.79*17 + 0.21*8 ≈ 15. As the averagereservoir age for those individuals was about 425 years, the reservoir age for 100% riverine food is expectedto be 540 years, as 540 * 0.75 ≈ 425 (Bonsall, Cook, Hedges, Higham, Pickard, and Radovanovic 2004).

1.3 Isotopic fractionation and stable isotope analysis

All isotopes of an element have similar chemical properties and can for example form the same kinds ofmolecules. They consist of the same number of protons. As atoms are neutral, isotopes of one element havethe same number of electrons, too. This is the reason for the similar chemical properties, as the electronsare responsible for the formation of molecules. The name “isotope” consists of the Greek words isos=equaland topos=place, because isotopes of an element are situated at the same position of the periodic table ofelements. The differences between the isotopes of one element are the mass and physical properties, becausethe isotopes contain different numbers of neutrons. The mass of a 13C atom is for example 8% greater thanthat of 12C, whereas 14C is 17% heavier than 12C (Browman 1981). Although the mass differences do notchange chemical properties totally, they can change reaction rates, because heavier isotopes are not as mobileas lighter ones. Isotopic fractionation (in the following shortened to fractionation) is the enrichment of acertain kind of isotope of an element. Evaporation, for instance, is a fractionating process, as the remainingliquid is enriched with heavier isotopes. Fractionation is enlarged with a bigger mass difference. Therefore,the extend of fractionation caused by isotopes of a certain element is the greater the smaller the moleculesare that contain this isotope. Fractionation between the different carbon isotopes is for example big whenCO2 diffuses into leaves, but is smaller for the transport of photosynthesis products like sucrose C12H22O11,where the exchange of one carbon atom with another isotope does not affect the molecular mass so strongly.

I will restrict the following discussion of stable isotope measurements to the stable isotopes of carbon,13C, and nitrogen, 15N. These stable isotopes are most used in archaeological research, and they are also theones I examined on my archaeological samples.

Stable isotope diet analysis began in the 1970s, after the different fractionation between C4 (in this casemaize) and C3 plants had been observed (Tykot 2003). Measurements of stable isotopes make it possible to

21

reconstruct past diets. A population that mainly lived on C4 plants is expected to have other δ13C valuesin their bones as a population that mainly lived on C3 plants. There are also differences in the 13C or 15Nvalues in bones of populations that lived mainly on terrestrial or marine food, respectively. First, the stablecarbon isotope 13C will be discussed.

1.3.1 13C

The measurement of the 13C value of a sample can be used for more than past diet reconstruction. Frac-tionation of carbon isotopes has to be taken into account for radiocarbon dating, because it influences the14C/12C or 14C/13C ratio which is used for calculating the age. When measuring the 13C content of a sam-ple, one can estimate from this the extent of fractionation that affected the carbon. As the mass differencebetween 14C and 12C is approximately twice the mass difference between 13C and 12C, one can assume thatfractionation affects 14C twice as much as 13C. The 13C content of a sample is measured compared to that ofa standard and noted in the form δ13C = (13Rsam −13 Rstd)/(13Rstd) ∗ 1000h where 13Rsam and 13Rstd arethe isotope ratios of the sample and of a standard, respectively. The standard most often used is Cretaceousbelemnite from the Peedee formation in southeast USA. It was formed during the Cretaceous period fromthe fossils of the marine cephalopods Belemnoidea, in this case Belemnitella americana (Tuniz, Zoppi, andBarbetti 2003)). So, 13C values are reported in the δ-notation “with respect to Peedee belemnite”, abbre-viated wrtPDB or just PDB. As the original PDB standard material is exhausted, newer measurements arereported with respect to another standard: “Vienna PDB”, abbreviated VPDB. It was calibrated againstthe standard material NBS 19, which also is a carbonate. The δ-notation is also used for the notation ofother isotope ratios, with the suitable standard for the particular isotope.

Fractionation processes of 13C will be regarded in the following, beginning with atmospheric CO2, andending in plants, animal and human bones, and soils. The fractionation mechanisms describes in the followinghave similar effects on 13C and 14C, so that the 13C fractionation can be used for correcting the 14C age.Informations about 13C measurements and fractionation were taken from Lanting and Van der Plicht (1996)and Clark and Fritz (1997), if not indicated differently.

The first big fractionation from atmospheric carbon takes place during photosynthesis, i.e. during CO2

diffusion into the leaf stomata and dissolution in the cell sap, and during carboxylation (carbon fixation)by the leaf’s chloroplast, where CO2 is converted to carbohydrate (CH2O). This results in a depletion of13C and 14C. The degree of depletion depends on the photosynthesis pathway and results in a 5 to 25hdepletion of δ13C. The radiocarbon standard of 100 pmC for example is calibrated to wood that grew in1890 and has δ13C=-25h. The δ13C value of atmospheric CO2, prior to the combustion of fossil fuel, wasabout -6.4h. The δ13C depletion in this case is thus 18.6h. The strong fractionation during photosynthesisthat causes this depletion of 13C will also affect the 14C. It is assumed that the fractionation for 14C is twicethe fractionation for 13C so that atmospheric CO2 was 37.2h enriched. If the mass factor of 2.3 instead of2 is used that was determined by Saliege and Fontes (1984), the atmospheric CO2 was even 42.8h enriched.

The oldest photosynthesis pathway, called Calvin or C3 cycle, is particularly suited to wet and mesophytic,i.e. moderately humid, environments (Browman 1981). It is called C3 cycle because the first product ofphotosynthetic CO2 fixation is a 3-carbon-compound (Hibberd and Quick 2002). It operates in about85% of plant species, including most trees and agricultural plants. Plants growing higher than 40 degreesof latitude use exclusively the C3 cycle. The C3 cycle is the cheapest energy path for photosynthesis anddeveloped when the earth’s atmosphere contained more CO2 than today. C3 plants fix CO2 with the Rubiscoenzyme, which also catalyses CO2 respiration through reaction with oxygen. In the present day’s atmosphereis CO2 respiration an inefficiency, only remaining as an artefact from development in an atmosphere withhigh CO2. Diffusion and dissolution of CO2 lead to a net enrichment in 13C, whereas carbon fixation leadsto a 29h depletion. The δ13C values for C3 plants end up as -24 to -30h with an average of about -27h.C3 plants are preferred by herbivores because they are more digestible. Overgrazing causes therefore plantswith other photosynthesis pathways to become dominant.

The more efficient C4 pathway evolved as atmospheric CO2 concentrations began dropping in the earlyTertiary. Under low CO2:O2 conditions and at higher temperatures, increased respiration in C3 plantsinterferes with their ability to fix CO2. C4 plants add an initial step where the PEP carboxylase enzyme

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Figure 1.7: Ranges for δ13C values in selected natural compounds (Clark and Fritz 1997)

[Phosphoenolpyruvate carboxylase] acts to deliver more carbon to Rubisco or for fixation. The name C4

comes from the 4-carbon-compound which is the first product of photosynthetic CO2 fixation. After itsdiscoverers, this pathway is also called Hatch-Slack cycle. C4 is a partly closed system and not able todiscriminate as completely against the more energy-expensive heavier isotopes as C3. One could also say,it is capable of using all isotopes and is therefore more efficient. C4 plants incorporate so a bigger ratio of13C and 14C than C3 and appear too young when they are compared to contemporaneous wood samples.They have δ13C values of -12.5h in average, ranging from about -10h to about -16h. 5% of plant speciesare C4 plants. They dominate in hot open ecosystems such as tropical and temperate grasslands. Someimportant agricultural plants like sugar cane, corn and sorghum are C4 plants. Some C3 plants might havethe potential to develop C4 photosynthesis, as recently was found out for tobacco. Cells which are far awayfrom the stomata through which atmospheric CO2 enters the plant are provided with CO2 from the cellsap. These photosynthetic cells possess high activities of enzymes characteristic of C4 photosynthesis, whichallow the decarboxylation of four-carbon organic acids from the xylem and phloem, thus releasing CO2 forphotosynthesis. These biochemical characteristics of C4 photosynthesis in cells around the vascular bundlesof stems of C3 plants might explain why C4 photosynthesis has evolved independently many times (Hibberdand Quick 2002).

Another photosynthesis pathway developed under water stress in arid regions: The Crassulacean acidmetabolism (CAM) cycle which is used by about 10% of plants. This pathway sometimes operates as an openand sometimes as a closed system, determined by environmental conditions. Therefore, it is well adaptedto water-stressed environments. CAM plants have the ability to switch from C3 photosynthesis during theday to the C4 pathway for fixing CO2 during the night. Many CAM plants can shift to a C3-like mode ofphotosynthesis when there is enough water so they can grow faster (Browman 1981). The δ13C values ofCAM plants span therefore the whole range of C3 and C4 plants, usually having intermediate values. Infigure 1.7, the ranges for δ13C values of different materials are given, including the atmosphere, plants withdifferent photosynthesis cycles, and soil CO2.

Further fractionation takes place along the steps of the food chain, although δ13C values generally onlyincrease only with less than one permil (Schoeninger and DeNiro 1984). Even in different materials from thesame organism, different δ13C values can be found. An African browsing ungulate, for example, had a δ13Cvalue of -21.2h for the bone collagen, but -28.9h in the fat (Browman 1981). Proteins in tissues of the

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consumer are derived from proteins in the food, and carbonate in bone apatite is derived from blood CO2

and ultimately from all energy supplying components in the diet, including excess protein. The carbonatefraction therefore reflects the mean isotopic composition of the whole diet. Experiments with rats showthat δ13C values in bone collagen not only depend on the δ13C values of the protein in the food but alsoon the amount of protein and on the difference in δ13C values of protein and non-protein fractions. Theδ13C values in bone collagen could thus overestimate the amount of protein in the food, especially when thiscontains small amounts of protein. The explanation is that proteins are used in the first place to producetissues like collagen, and are only used as energy suppliers in case of excess. This means that linear mixingmodels, using values of δ13C in bone collagen of the consumer, and in the different components of thediet, cannot be used in paleo diet studies. “On the other hand, δ13C in carbonate in bone apatite reflectsthe whole diet composition with such fidelity that it should be routinely analyzed along with δ13C in bonecollagen” (Lanting and Van der Plicht 1996). The δ13C value might thus overestimate the amount of proteinsin the food, but it is already interesting enough to examine how a population got the proteins they needed,for example regarding the question if marine resources played a big role in a certain culture.

Food chains in marine and freshwater environments are different, and so are isotopic values. Althoughthe difference is biggest for 15N (see section 1.3.2), one can also see a small difference in 13C values. δ13Cvalues for marine animals are in average 5.5h less negative than for terrestrial animals, but there is anoverlap of 8h between the two groups, so that they are not very sharply devided. Animals which at leaststay a part of their life in freshwater have more or less terrestrial δ13C values, maybe because terrestrialcarbon is incorporated by the freshwater organisms (Schoeninger and DeNiro 1984). Humans, for example,who live mainly on marine food have δ13C values in their bone collagen of -13±1h (Lanting and Van derPlicht 1996). Chisholm, Nelson, and Schwarcz (1982) expected δ13C values of -13h for purely marine and-20h for purely terrestric nutrition. One surprising example for the application of 13C measurements fordiet reconstruction are 13C measurements from many Mediterranean coastal sites where the 13C values were“not consistent with marine food consumption as a staple during the Mesolithic, Neolithic, or Bronze Ageperiods” and “seafood [was] only measurable important for some Mycenae elites” (Tykot 2003). At theend of freshwater food chains, δ13C values in bone collagen are expected to be between -24h in lowlandrivers and -20h in lakes and canals. δ13C values of bone collagen give a mean value over the last 10 yearsbefore death because of the long turnover times of bone collagen. In areas where both C3 and C4 plants aregrowing, those animals feeding on a mixture of marine and terrestrial foods could not be distinguished fromthose feeding exclusively on terrestrial foods (Schoeninger and DeNiro 1984).

Because of the above-mentioned effects, it is hard to find out what a person really lived on by measuringδ13C of bone collagen, as Lanting and Van der Plicht (1996) explain: “With δ13C values alone it is notpossible to decide whether less negative values are caused by consumption of marine fish or of C-4 [C4] food,or whether values around -21h are the result of an almost vegetarian diet or of consumption of terrestrialmeat and freshwater fish”. A high consumption of a mixture of seafood and freshwater fish gives δ13C valuescomparable to a completely terrestrial diet. 15N measurements (see section 1.3.2) can help deciding suchquestions because δ15N is far more positive in fish than in terrestrial food. Even if the diet contains only alow protein content, most of the carbon in collagen comes from the protein (Ambrose 2001). In tidal watersand estuarine systems, a “run-off effect” of biogenic carbon can happen which causes the δ13C values inthese areas to have terrestrial values (Chisholm 1989). People living mainly on fish could so have the sameδ13C values as a population which is living solely on terrestrial food.

The decay of organic material in the soil does not lead to further fractionation. Aerobic bacteria convertmuch of the organic material back to CO2, and this CO2 has much the same δ13C concentration as thevegetation itself. The CO2 concentration of soils is 10 to 100 times higher than that of the atmosphere, andit is diffusion of CO2 along this steep concentration gradient that results in a 13C enrichment of the soils.δ13C in soils hosting C3 plants is about 23h, whereas it is -9h in a C4 landscape (Clark and Fritz 1997).

1.3.2 15N

There are only two natural nitrogen isotopes: 14N and 15N, while the mass numbers of artificial radioactivenitrogen isotopes span from 12 to 19. 99.634% of nitrogen in atmospheric air consists of 14N, 0.366% of 15N.

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The 15N isotope was discovered in 1929. Since the first experiments in 1943, it was used as indicator forinvestigations of the nitrogen cycle in cropping soils and plants as well as for investigations of the conversionof proteins. 15N is, just like 13C (see above) expressed in the delta notation. The standard material for 15Nis atmospheric air.

There is a step-wise increase in 15N between trophic levels (Ambrose 2001). This means that there is 15Nenrichment from plants to herbivores to carnivores. Marine and freshwater zooplankton, for example, δ15Nvalues that are on average 3h more positive than associated phytoplankton (Schoeninger and DeNiro (1984)and references therein). In marine systems, food chains are generally longer so that more 15N enrichmentsteps can take place as in terrestrial systems. Enrichment between to steps in a food chain is normally about3h, as is the case for plankton, but there are big differences between species and even between differentgroups (Ambrose 2001). The reason for that is that trophic levels within food webs can overlap to a largeextent (Schoeninger and DeNiro 1984). It is possible to reconstruct the trophic level of animals which areexclusively feeding on terrestrial or exclusively feeding on marine food with their δ15N values. Schoeningerand DeNiro (1984) observed that marine animals “with bone collagen δ15N values less than +13h fed oninvertebrates whereas those with δ15N values greater than +16.5h fed on other vertebrates”. Schoeningerand DeNiro (1984) give some examples of average δ15N values in bone collagen (table 1.1).

Table 1.1: Average δ15N values in bone collagen of different terrestrial and marine animals (Schoeninger andDeNiro 1984)

Carnivorous terrestrial animals +8.0hHerbivorous terrestrial animals +5.3hMarine animals feeding on fish +16.5hMarine animals feeding on invertebrates +13.3hFreshwater fish feeding on fish +8.0hMarine fish +11.4 to +16.0hMarine birds +9.4 to +17.9hMarine animals in total +9.4 to +23.0hTerrestrial animals in total +1.9 to 10.0h

The overlap between terrestrial and marine animals is only 1h and the mean for marine animals is almost9h more positive than the mean for terrestrial animals. The reason is, as mentioned above, the differencelength of food chains in marine and terrestrial systems. If only mammals are considered, the differencebetween the mean values is bigger by almost 10h. Additionally, there is not an overlap between the tworanges but they are separated by about 2h.

As virtually all of the nitrogen that humans assimilate is derived from protein, δ15N values recorded inthe human bone collagen allow to reconstruct past diets and for example calculate how much protein inthe humans’ nutrition derived from aquatic and how much from terrestrial animals (Bonsall, Cook, Hedges,Higham, Pickard, and Radovanovic 2004). This would be impossible if the nitrogen assimilated in humanswould derive from for example air.

1.4 Food residues on pottery

Pottery is one of the most important categories of archaeological finds and often used for the definition andseparation of archaeological cultures. Potsherds are often the most plentiful artefacts found in archaeologicexcavations, can form the basis of useful chronologic sequences used to trace the development of a regionor culture (Johnson, Stipp, Tamers, Bonani, Suter, and Wolfli 1986), and are used as markers to correlatewidespread sites and summarize the overall development of diverse civilizations or cultures. The dating ofpottery that was found at a certain site gives valuable information about the occupation endurance of that

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site, because it is directly related to human activity. In contrast to that, charcoal for example could stemfrom old wood, such as drift wood, dead wood collected in a forest, or the inner parts of a log and so providetoo high ages. Before explaining 14C dating of food crusts on pottery, I will give an introduction to potteryas an archaeologic material and explain basal terms.

1.4.1 Terminology and general remarks on prehistoric pottery

Tite (2003b) gives a comprehensive introduction to prehistoric pottery. A big part of the informationpresented here is derived from his text. The first step in pottery-making is the preparation of the clay. Itshould be sufficiently plastic for forming, but its drying shrinkage should be limited to minimize the dangerof cracking. Therefore, in some cases clays with different properties can be mixed, while in other casesnon-plastic inclusions have to be removed or temper has to be added. Temper usually consists of more orless fine material which is capable of absorbing the water that gets released from the pottery while firing.This water can come from the pores between the clay minerals (the fraction that did not evaporate whiledrying) or from inside the minerals (this water can not be removed with drying the pottery and is onlyreleased at high temperatures). If the water evaporates, the pot shrinks while water vapour fills the pores.This would then cause the pot to crack.

Some examples of temper that prevent the pot from cracking are sand, grog (i.e. crushed sherd), organicmaterial (e.g. chaff), crushed flint, shell or limestone. The temper is often exclusively of one kind for acertain ware, sometimes even having a symbolic value: Grog temper, obtained from the crushing of ancestralpottery, for example, can be seen as an act of “rebirth” through which a “reversal of time” is achieved.

There are different methods of forming the lump of clay into a pot, for example pinching, drawing orbeating (using a paddle and anvil); pressing or pounding into a mould; building up from coils or slabs; andthrowing on a wheel. The pottery of the examined period is built up from coils (see section 3.3.4), whichcan for example be seen on the sides of the sherds and on the shape of cracks. It is likely that in theNeolithic, a household production of pottery took place. This can be inferred from the simple shapes andbuilding technique of the pots as well as from a limited standardization in the raw material composition.The pots were hand-formed and open-fired in a bonfire, so that they easily could be made by part-time,non-specialist potters. There are ethnographic examples, though, that hand-formed, open-fired and notdecorated or specialized pottery is made by a specialized group of people (Haland 1979).

1.4.2 Dating of pottery

The oldest method of pottery dating uses style and technique to build up chronologies. A precondition forthis dating method is that different pieces of pottery, looking the same and made and decorated in the sameway, are contemporaneous. Another is that changes only occur gradually, so that it is possible to build upa so-called “typological sequence”. Apparently, people in certain cultures and in certain times all used thesame techniques and shapes for producing pottery, although many different kinds of pottery would serve thesame purpose. As Hayashida (2003) remarks, “There may be many ways to make a sturdy cooking pot givenavailable materials but the particular clays chosen and the techniques used to form, finish, and fire the vesselsare linked to such diverse factors as the organisation of the potters, their social identity, the perception ofdifferent raw materials and fuels, and the integration of pottery-making with other activities”. This methodis the least expensive one and done by the archaeologist himself so that the result is immediately available.However, this method only provides relative datings and is subjective. For absolute datings, other scientificmethods have to be applied.

There are different physical methods for dating of pottery. Thermoluminescence (TL) dating is oneexample. It dates the moment of the last heating of a sample containing minerals, as the firing of pottery.A thermoluminescence signal builds up as a mineral is exposed to natural radioactivity. The TL signalis zeroed when the mineral is heated. When zeroing a mineral in the laboratory, a measurement of thethermoluminescence signal, the amount of light emitted by the mineral, is a measure for the time since thelast zeroing. The advantage of TL dating is that it avoids the “old charcoal problem” and that it is not soexpensive as AMS. Limitations are that a sherd “may have been accidentally reheated after original firing”,

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that it “may not have been completely zeroed in ineffective firing” and that “some ceramics do not holda TL signal” (Johnson, Stipp, Tamers, Bonani, Suter, and Wolfli 1986). Also when applying radiocarbon,some restrictions have to be taken into account. Nonetheless, I now will focus only on radiocarbon and notdescribe other methods in more detail.

The main restriction when trying to radiocarbon-date pottery is the limited extent to which carbon canbe found in pottery. Radiocarbon dating of pottery was first made possible with the introduction of AMS(see section 1.2). Conventional 14C dating (with beta-decay-counting) could only be applied to associatedsamples of another material, for example charcoal, or implied the destruction of large quantities of sherdmaterial (Johnson, Stipp, Tamers, Bonani, Suter, and Wolfli 1986). Other problems originate from thevariety of possible carbon sources and the different points in time they belong to: carbon originally presentin the clay, carbon added as organic temper, carbon from soot deposits made during manufacture or use,carbon from food residues, and secondary carbon contamination after deposition (Feathers 1993). All thesedifferent carbon sources may have different ages (Hedges, Tiemei, and Housley 1992). Pottery normallyconsists of 50 to 70% clay. Carbon originally present in that clay has normally infinite ages, although it canbe younger (a few thousand years) when it closely underlies surface vegetation. In each case, it tends toincrease the apparent age of the potsherd. Quarried clays may contain up to 20% organic matter. 20 to 50%of a potsherd consist of temper which is likely, but not exclusively, contemporaneous with the production ofthe pottery. If consisting of organic matter, temper is generally useful for dating. Though being useful fordating, it is not very probable that enough temper survives the firing process. Gabasio, Evin, Arnal, andAndrieux (1986) studied modern pottery with known composition of clay (known carbon content), differenttemper and different amounts of organic admixture. Experiments with reconstructed neolithic kilns showedthat the addition of up tp 10% organic matter did not change the carbon content of the pot after firing. Inthe case of the pottery examined in this thesis, granite chippings were used as temper. The temper providesthus no carbon contemporary with the pot for radiocarbon dating. Carbon from soot deposits made duringmanufacture is also regarded as useful for dating although the old wood effect has to be taken into account.The more porous a pottery is, the more soot can be deposited during firing. Also the use of primitivekilns enlarges the fraction of carbon deposits in the pottery, because pottery in primitive kilns is in directcontact with the fuel. Generally, the fire in primitive kilns is fed by wood or dry grass so that a lot of sootdevelops. It is therefore expected that pottery of protohistoric times contains enough carbon from the fireto date the firing process whereas more advanced pottery from historical times is expected to be difficult todate (Gabasio, Evin, Arnal, and Andrieux 1986). However, pottery from historic epochs can normally bedated more easily and precise by style than by scientific methods.

There are two datable moments when analysing pottery: The firing and/or last heating as well as thelast use for processing food. It is hard to date the firing of the pottery with radiocarbon, because it is notcompletely clear which material is associated with that process. One possible material is organic temper, ifit had been used and did not burn away completely (see above), and if it can be extracted from the sherd.Often only imprints of burnt temper particles remain. But even if present, organic temper is hard to separatefrom other organic material that was in the clay long before it was formed and burned (the organic materialcould even originate from the time of formation of the clay). The carbon in the clay can thus have geologicalages (Hedges, Tiemei, and Housley 1992).

Carbonaceous compounds such as humic acids can be introduced from the burial context. Althoughthis is regarded as contamination, it possibly tends to reflect the date of the burial stratum and oftendoes not seriously alter the dating of the sherd. Bacterial activity has also to be taken into account if thesherd was buried in an organic-rich deposit (Hedges 1992). Bacteria, though, normally do not change theisotopic composition of the carbon to a significant extent because they use carbon from the sample insteadof introducing carbon from other sources.

The last use for processing food can be dated when a crust of charred material is found on the sherd.As a pot with a thick, charred crust is not best suited for the preparation of well-tasting food and as it isimpossible to completely clean such a porous pot, one can assume that the pot was not used for a long timeafter the formation of the crust. Apart from its potential for dating, the existence of food crusts providesthe knowledge that the examined type of pottery was used for the processing of food and not, for example,

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only for carrying or storing water (Andersen and Malmros 1984). Because the sherds appear thick, fragileand porous when excavated, it was doubted for some time that the pots had been suitable for cooking.Klinge (1932)for example tried to boil water in rebuilt Ertebølle pots, but he did not succeed because thewater was evaporating through the pores of the pot already at 70-90◦C. Therefore, he concluded that thepots were only used as salterns for sea water. Later findings of Ertebølle pots in the inland, far away fromsupplies of sea water, contradicted this interpretation. Later experiments in which starch or fat had beenadded to the liquid in the pot also disagree with Klinge’s conclusion: the pores of the pot were sealed withstarch or fat so that the content could be heated up to the boiling point (Andersen and Malmros 1984).Our experiments support this statement and show the suitability of Ertebølle pots for food processing (seesection 4.1.3). In contrast to that, a charred crust on the inside of a pot can have a completely differentreason, as ethnographical observations indicate: In Western Sudan, simple clay pots have been waterproofedby filling them with grass or stray before firing them upside down. The soot layer in the pots preventedwater from soaking through the pores so that the pots were suitable for boiling water (Haland 1979).

On many pots of the Late Mesolithic Ertebølle culture, crusts of charred organical material are preserved,especially in coastal and bog areas. In the material from Schleswig-Holstein, food crusts from pots at coastalsettlements are always thicker than those from inland sites, an observation that is not yet understood (pers.comment S. Hartz 2007). A possible reason could be the better preservation environment for organic samplesat coastal sites so that the food crusts there stay more intact than those from inland sites. As the crustsare charred and the thickest crusts occur on the inside of the pots, especially in the bottom half of the pots,they are interpreted as burnt food remains and therefore called food crusts. Crusts on the upper outside ofthe pots are explained to come from a liquid content boiling over, for example a soup. The reason for theabsence of such crusts on the outside of the bottom half of the pot could be that the food remains therewere completely charred away by the hearth fire (Andersen and Malmros 1984). Crusts on the outside ofthe pots could also come from soot, when the food was prepared over an open fire. The soot is expected togive the same or a higher age as the pottery, depending of the kind of fuel that was used (short-lived organicmaterial or old wood).

One example for the dating of food crusts from the EBK is the submarine settlement Tybrind Vig onthe western coast of the island Fyn in Denmark. The pottery at this site was embedded in the gyttja of thewaste zone and is therefore well preserved. The site is radiocarbon dated to 4400-3200 BC (in uncalibrated14C-years), whereas the pottery is from 3700-3500 BC (in uncalibrated 14C-years) (Andersen and Malmros1984). The calibrated date for the site is approximately 5400-4000 BC and for the pottery approximately4500-4350 BC.

A possible hardwater effect on pottery has been shown by Fischer and Heinemeier (2003), see section 1.2.2.Pottery dating from Estonia has in one case given a date that was 1000 years older than expected (Kriiska,Lavento, and Peets 2005). It could be that this dating is correct and that the archaeological assumptionhas to be corrected, but it could as well be that the hardwater effect contributed to the high age of thepottery which was found on a site at a river bank (Kriiska, Lavento, and Peets 2005). Nakamura, Taniguchi,Tsuji, and Oda (2001) report ages as high as 15,710-16,540 cal BC for the earliest Japanese pottery. It hadbeen assumed before that the use of pottery started with the Jomon Culture in the Holocene after a seriesof climatic fluctuations. The AMS dating of pottery, though, suggest that the first pottery was alreadymade during a cold climate period “predating such climatic fluctuations by about a millennium”. It wouldbe interesting to examine this pottery closer to find out if it also had been influenced by the hardwatereffect or if those surprisingly high radiocarbon ages also correspond to high historical ages. Up to now, theyounger ages of charcoal samples have been explained with the assumption that these charcoal pieces reallyare younger and have been anthropogenically or naturally mixed into the layers in which the pottery wasfound (Nakamura, Taniguchi, Tsuji, and Oda 2001).

It has been tried to extract protein for food crust dating from some Swedish sites (Segerberg, Possnert,Arrhenius, and Liden 1991). For obtaining one milligram carbon, 1 gram food crust is needed from whichproteins are extracted with the “Lowry”-method. Amino acids are split using high performance thin layerchromatography (HPTLC). From the resulting 3 mg amino acids, 1 mg carbon can be gained. The surprisingresult of the amino acid extraction was that the amino acid which normally is most abundant in all nutritives,

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glutamine, was totally absent on one sherd and only detectable on another one. Alanine, though, a simplenon-essential amino acid, was found in large amounts on another sherd. This can be explained by the factthat alanine is the simplest of all amino acids and large quantities of it are present in strongly deterioratedproducts. The amino acid composition of the potsherds is thus an indicator for the fact that they are brokendown by natural or man-made processes.

Another attempt is the extraction of lipids from the entire sherd. Hedges, Tiemei, and Housley (1992)tried this using Soxhlet extraction in acetone. Many of the archaeological sherds they examined containedextractable lipids at the level of 0.02 to 0.4% and seem to be a good dating material. Lipids are ratherimmobile and lipid concentrations in soils are low so that little exchange between sherd and burial contextcan be expected. Nevertheless, only 3 out of 7 examined sherd provided reasonable (not necessarily accu-rate) lipid ages. Therefore, they only denote food crusts as “fairly reliable” samples if no organic temperremained. Stott, Berstan, Evershed, Hedges, Bronk Ramsey, and Humm (2001) also used lipid extractionfor radiocarbon of potsherds but they extracted different fatty acids from the sherd material. Stearic (C18:0)and palmitice (C16:0) acid and the C18:1 unsaturated acid provided high enough concentrations for radio-carbon dating when examining potsherd samples of about 10 g. After extraction, the lipids were derivatedand purified. Gas chromatography (GC) was used for extracting the single fatty acids. This method provedto be very time-demanding: To obtain sufficient material for precise dating repetitive, accumulating, GCseparation is necessary. About 100 runs were needed for each sample.

1.4.3 Analyses on food crusts

Organic residue analysis gives information both on the use of the pottery and on past diet and has therefore“the potential for contributing to our understanding of the reasons for the adoption of pottery in differentregions” (Tite 2003b).

13C analyses of food crusts from Tybrind Vig showed terrestrial origin (two samples had -22.1h, one-26.6) although the visible remains mainly came from cod (scales and bones) and to a smaller extent fromgrass. This was interpreted as the remains of a fish soup with a big fraction of terrestrial plants (Andersenand Malmros 1984). Also Arrhenius and Liden (1989) found bones and scales of fish on the pottery, but thelow protein content, the high fat content and the presence of phytoliths indicate that “fermented porridgeof vegetable origin” (Arrhenius and Liden 1989) was prepared in the pots. One crust had 47% lipid content,but only 1.08% protein content. Protein content in some recent reference material (Baltic herring) wascomparably low, but the authors claim that with the ageing of the sample, normally a protein-enrichmenttakes place. A conclusion could be that the pots first were used for the preparation of plant food and lateras waste bins for fish rests. The fact that macrofossils found by Andersen and Malmros (1984) were onlypresent in the upper layers of the food crusts indicates that they came into the pot after the formation of thecrust. Otherwise would they have been sunken to the bottom of the pot. The fact that they are imbeddedin the crust, though, indicates that they were put into the pot when the crusts still was wet (Arrhenius andLiden 1989).

The protein composition of the pots investigated by Arrhenius and Liden (1989) from Tybrind Vig showa similar pattern. Dominating are alanine, glycine, methionine and to a certain extent also glutamic acid.Alanine, a simple nonessential crystalline amino acid, can be found in high concentrations in animal products,nuts and mushrooms and even in decomposed materials. Glycine is a sweet crystalline amino acid obtainedespecially by hydrolysis of proteins and can be found in high concentrations in animal products. Methionineis a crystalline sulphur-containing essential amino acid that mainly can be found in nuts. Glutamic acid, acrystalline amino acid, is widely distributed in plant and animal proteins and is the dominating amino acidin all food products, except some fruits and roots.

The amino acid cysteine, which is characteristic for fish, is completely missing in the material fromTybrind Vig which again is an argument against Andersen’s and Malmros’ (1984) interpretation of charredfish soup remains. According to Arrhenius and Liden (1989) are bubbles in the crusts further evidence forfermented porridge. The high fat content of the crusts could indicate the use of plant oil such as beech-nutoil (Arrhenius and Liden 1989), but it could also be a question of conservation: “Because of their hydrophobic

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properties, lipids survive on pottery and the migration of lipids from the soil in which the pottery was burieddoes not normally seem to occur to any significant extent” (Tite 2003b).

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Chapter 2

Small sample preparation

Some of the sample types that are analyzed in this work are quite small. The normal sample size requiredfor 14C dating is 1 mg carbon. Fishbones and food crust, though, are expected to yield smaller carbonmasses. The carbon mass of these sample types was often below 200 µg and in one case only 30 µg. Alsosome bones of terrestrial animals had so small carbon yield, when the samples were quite small and badlypreserved. A detailed description of the samples can be found in section 4. The smallest sample mass thatnowadays is routinely dated at the AMS 14C laboratory at Aahus university is 350 µg carbon. For being ableto measure the samples mentioned above, instrumental development was thus needed to reduce the samplesize. For seeing if such a sample size reduction is possible in principal, the results of other groups have beenchecked. It has been reported that samples as small as 50 µg carbon can be measured without significantisotopic fractionation. Also the measurement of samples with 15 µgC should be possible, but the introducedfractionation must then be corrected by processing and measuring standards of the same size (Tuniz, Zoppi,and Barbetti 2003). It is thus worthwile optimising our equipment to the preparation of samples in the rangeof few tens of micrograms.

I will take a look at all steps in sample preparation. I will also include the steps where I did notdevelop new techniques myself to obtain a complete description of the sample preparation. There are twofundamental steps in sample preparation. The first is the removal of contamination from the sample. Thisstep is also called chemical pretreatment or simply pretreatment. The second step is the conversion of thepretreated sample to a form in which the abundance of 14C can me measured. In our case, this is elementalgraphite. After the chemical pretreatment, the sample is thus combusted to CO2 which then is reduced sothat elemental carbon, graphite, is obtained. This last procedure is called “graphitisation”. First, I will takea short look at the chemical pretreatment. Then, the graphitisation of small samples will be examined. Theinfluence of the material that catalyzes the reaction will be analysed. A reduction of the reaction volumewill be shown to provide better conditions for the graphitisation of small samples. In the end, an outlook toa new combustion method that combines the production of CO2 for 14C measurement with stable isotopeanalysis will be presented.

A constant amount of contamination introduced during the sample preparation process is as bigger aproblem as smaller the sample mass is. As each step in the sample preparation bears the risk of contaminationand/or fractionation, each step has to be optimised for small samples. A reduction in the sample preparationeffort would not only save time and money, but also help getting better results with reducing the numberof steps in which fractionation or contamination could be introduced. This applies also to the chemicaltreatment: as many steps as needed to get rid of most of the contaminants have to be applied, but as fewas possible to reduce the risk of laboratory contamination.

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2.1 Sample pretreatment

A good overview over sample pretreatment can be found in Hedges (1992). Some of the information presentedhere has been extracted from that paper. The basic assumptions in radiocarbon dating include after Hedges(1992) the following:

1. The planetary distribution of 14C in the biosphere is uniform in time and space;

2. The sample, as measured, contains carbon that came only from a living organism (or similar systemthat ceases to be in chemical exchange with the biosphere), and that the living organism took itscarbon only from the biosphere

The first assumption is only approximately true, but can be corrected (see section 1.1.3 and 1.2.2). To besure that the second assumption is right, one has to remove all the contaminants from the sample and onlyuse the most reliable fraction of the sample, for example the collagen from bones, for dating. Only thefraction of carbon that was incorporated during the organism’s life should be used for dating. A problemwith the second assumption is the hardwater reservoir effect which was described before in section 1.2.3:Carbon in the water organisms is not likely to be purely atmospheric. Contamination of a sample is theadmixture of carbon with a different 14C concentration to the sample. Contamination can to a great extentbe removed chemically. The chemical pretreatment thus isolates and purifies the chemical phase or phasesthat represent the ecent or archaeological culture or geologic stratum to be dated (Long 1992).

Some chemical pretreatment of the sample is needed, anyway, also if assuming that no contaminationentered the sample, as the sample has to be converted to another form: The chemical conversion of a samplein its pristine state to the form in which the abundance of radiocarbon can be directly measured is the mainlink between the radiocarbon date and the basic assumptions upon which this date rests. In the case of AMSat Aarhus University, the samples have to be converted into graphite, because that is the form in which theabundance of radiocarbon can be directly measured with the accelerator. So, after chemical preparation toremove contaminants, the samples are combusted to gain CO2 and then reduced to pure carbon (graphite).

Routine methods were developed for the pretreatment of samples for conventional radiocarbon datingand after some time been taken for granted. AMS brought about changes in pretreatment methods, bothbecause the sample is measured in another form (graphite instead of counting gas or liquid) and becausethe sample size is reduced by a factor of at least a thousand. This has stimulated a re-examination ofmany pretreatment methods, and thereby enabled the link between assumption and date to be more closelycontrolled.

Two important classes of contaminants that enter archaeological samples during burial are carbonatesand humic substances. Carbonates are transported with the soil water and can for example be incorporatedby the mineral fraction of bones, but they are also incorporated by other sample types. They can be removedwith acidifying the sample with hydrochloric acid, HCl. Humic substances are a fraction of the dissolvedorganic carbon in soils (see section 1.2.3). The characterization of different humic substances is largely basedon separation methods. Humic substances have the relatively high molecular weight in common that canbe up to several 100,000 mass units, or several 100kD. They are refractory, heterogenous, alkali soluble andgive the dark colour to soil and water (Clark and Fritz 1997). Humic substances include humic acids, fulvicacids and insoluble humic substances. Humic acids precipitate from solution at pH < 2. Fulvic acid issoluble at all pH values. Both humic and fulvic acid derive from humification of vegetation, for examplefrom cellulose and other carbohydrates, proteins, lignins and tannins, by bacterial metabolism and oxidation.Humic substances are removed with sodium hydroxide, NaOH, from the samples.

The pretreatment methods that were used for big samples were adjusted slightly to pretreat smallersamples. The concentration of NaOH was for example weaker for the smalles samples so that the danger ofdissolving the sample completely was minimized (see section 4).

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2.2 Graphitisation of small samples

The samples have to be converted into a form in which the abundance of 14C can be measured directly. ForAMS measurements, the samples have to be pure carbon, i.e. graphite. To obtain this graphite, the sampleis first combusted or acidified to form CO2 and then reduced to get pure carbon (or graphite) after thereaction CO2 + 2H2 = 2H2O + C. This reaction will in the following be called “graphitisation”.

This reaction can only take place in the presence of a catalyst. Here, cobalt and iron are used. Theyserve not only as catalysts, but also as carrier material for the measurements in the accelerator. Theyhave different properties, as will be explained in the following. The catalyst is filled into the reaction tube(“reactor”) before the sample CO2 comes in. With the help of a magnet, the catalyst particles get raised upso that the reaction surface gets bigger. The reactor with the catalyst is then evacuated and 380 to 400 torrH2 are filled in to prepare the catalyst. H2 remains for one hour in the reactor at 400◦C. After that, the H2

is pumped away and the reactor is ready for the graphitisation of a sample.The combusted sample, in the form of CO2 in a quartz tube, has to be transferred to the graphitisation

system. For this, the quartz tube is placed into a tube cracker. This is connected to the graphitisation systemand is evacuated. After closing the valves to the pump, the tube is cracked and the sample transferred toa coldfinger with the help of liquid nitrogen. Nitrogen has a boiling point of -196◦C which is below thefreezing point of CO2 (-78.5◦C). On the transfer line, the sample has to pass a coldfinger which is cooled bya mixture of ethanol and liquid nitrogen. It has a temperature between -72 and -80◦C. Water vapour as wellas some other contaminating gases like H2S or SO3 which might have been in the sample freezes here andis so not transferred with the sample. The rest gas which can not be frozen at -196◦C is pumped away. Itis mostly sulphur and especially with bones, quite big percentages around 30% can normally not be frozen.Other samples such as oxalic acid or charcoal normally only contain minimal amounts of rest gas. When therest gas is pumped away and thus only CO2 remains in the cold finger, the coldfinger is closed off from therest of the system and the pressure is measured. From the pressure in this standardised volume, the carbonmass can be calculated.

From the coldfinger, a CO2 amount corresponding to approximately 1.1 mg carbon (mgC) is transferredto a reactor. About 0.2 mgC are transferred to a vial for 13C-measurements. These transfers also are donewith liquid nitrogen. Figure 2.1 shows the reactors. On the picure, Peltier coolers are already placed onthe glass tubes where water is frozen during the reaction. Before placing the Peltier coolers there, the sameglass tubes are used for transferring the sample with the help of liquid nitrogen. The CO2 pressure in thereactor is measured. For 1.1 mgC, it is around 440 torr at system 1 and 400 torr at system 2. The amountof H2 needed for the reaction is calculated:

pH2 = pCO2 ∗ 2.1 (2.1)

For the reaction CO2 + 2H2 = C + 2H2O, the H2 amount has to be twice as large as the CO2 amount. Thefactor is 2.1 instead for 2 in order to have a little H2 excess and definitely enough for so the reaction is ascomplete as possible. Moreover, a higher pressure at the beginning can accelerate the graphitisation process.The water which is produced in the reaction gets frozen with a Peltier cooler. The reaction normally takesplace at 700◦C and usually lasts a couple of hours and is therefore done overnight. On the next morning,after the ovens have been removed, the end pressure is written down. Thereafter, excess H2 and CO2 thatmight have not reacted are pumped away. The Peltier coolers are removed and the water vapor is pumpedout as well. To avoid that the first contact of the graphitised sample is with air and to make it easier toremove the (now evacuated) reactors, they are filled with Argon at atmospheric pressure.

The graphite yield or graphitisation efficiency is the ratio of the pressure difference for an actual reactionto the pressure difference of a theoretical 100% reaction. In the reaction CO2 + 2H2 = C + 2H2O, eachunit of CO2 reacts with two units of H2 so that after a complete reaction three units of pressure should bemissing and only the excess hydrogen should be left. The theoretical pressure difference of a 100% reactionis therefore three times the CO2 pressure. The graphitisation yield is defined after Hua, Jacobsen, Zoppi,Lawson, Williams, Smith, and McGann (2001) in the following way:

Graphite yield =Initial pressure− Final pressure

3 ∗ CO2pressure% (2.2)

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Figure 2.1: Normal-sized graphitisation reaction tubes. The peltier coolers are placed at the glass tube inwhich water is frozen. On top, a pressure transducer is installed. To the left, the green valve connects thereaction volume with the rest of the system. The reaction tube can be seen as the oven is not yet put uponit.

Applying this definition to our situation will not lead to precise values for the graphitisation yield because theinitial and final pressure are measured while the Peltier coolers are switched on, whereas the CO2 pressureis measured at room temperature. Anyway, it is a good indicator of reaction completion and can be usedto compare the yield of graphitisations which are done in different ways. Let us assume that a reaction wascompleted and that all pressures were measured at the same temperature. For 1 torr of CO2 in the reactor,2.1 torr H2 are filled in. The initial pressure is thus 3.1 torr. The final pressure is the initial pressure reducedwith the amount of CO2 and H2 that reacted, so that the final pressure for a completed reaction is 0.1 torrin our example. This is the result when calculating the graphite yield after equation 2.2 for this example:

Graphite yield =3.1torr− 0.1torr

3 ∗ 1torr= 1 = 100%. (2.3)

Two things are different when water samples are graphitised. The one is the water trap through whichthe sample is transferred. It has a temperature of about -110◦C instead of -72 to -80◦C. The second is thecatalyst: Instead of 0.8 mg, 1 mg cobalt is used and additionally, a small strip of silver foil is inserted into thereactor. Both modifications are due to the high water vapor concentration that is left in CO2 extracted fromwater samples. At a lower temperature, the water trap freezes water vapor more efficiently. As water vaporthat all the same reaches the reactor slows down the reaction with covering catalyst surface, the catalystamount is enlarged to provide reaction surface enough. Silver is used because it can react with hydrogensulphide H2S to water and silver sulphide and so remove the hydrogen sulphide from the reaction tube:

4Ag + 2H2S + O2 → 2Ag2S + 2H2O. (2.4)

The water originating from this reaction is frozen in the Peltier cooler in the same way as the water originatingfrom the graphitisation reaction, CO2 + H2 → C + H2O.

There are two factors which have to be optimized in the graphitisation process to obtain best conditions forreliable dating: The reaction time has to be as short as possible to minimize the risk of contamination throughair leaks and the reaction has to be as complete as possible in order to reduce the risk of fractionation (Smith,

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Petrenko, Hua, Southon, and Brailsford 2007) and to get maximize the graphite yield, i.e. the amount ofcarbon from the sample that can be used for dating.

In our laboratory, there are two graphitisation systems, called system 1 and system 2. System 1 comprises10 reactors, R10 to R17, R19, and R110 (read R1-0, R1-1, to R1-10). Eight of them, R10 to R17, are normal-sized (4.5 cm3) and the remaining two, R19 and R110, are small (0.8 cm3). It is planned to set up foursmall reactors on system 1 that will be called R18 to R111. Because of lacking fittings, only two of the smallreactors could be completed. That is the reason for the incomplete numeration of the existing reactors. Infigure 2.1, four normal-sized reactors are shown. On the picture, Peltier coolers are already attached tothem. Figure 2.2 shows the part of the graphitisation system where the two small reactors are installed.Figure 2.2b shows the reaction volume. In figure 2.2c, the Peltier cooler is attached. In figure 2.2d, alsothe oven is placed on the reaction volume. System 2 comprises 8 normal-sized reactors, R20 to R27. In thefollowing, system 1 has been used almost exclusively.

2.2.1 Experiments with the existing graphitisation system

For testing how small samples can be graphitised with the old system, graphite samples of different sizeswere combusted after the standard procedure (see page 48) and graphitised again. They were then comparedto the original graphite via measurements in the mass spectrometer to see if the 13C-content changes duringthe combustion/graphitisation and if these changes are dependent on the sample size.

After combusting the samples in that way, the CO2 was transferred to the graphitisation system andthe amount of carbon was determined via measuring the CO2 pressure in a calibrated volume. The amountof carbon before and after combustion for the graphite samples BP1 to BP8 is given in table 2.1. Smalldifferences in the amount of carbon are due to measurement uncertainties and loss during transfer. Thecombustion was apparently not complete for the small samples BP7 and BP8, so that further investigationis needed for the combustion of <0.3 mg samples.

The CO2 was reduced to carbon using hydrogen as reduction agent and cobalt as catalyst at 700◦C.From the graphite-cobalt compound, a fraction containing approximately 0.1 mg of carbon was put intotin cups to be measured at the mass spectrometer (the mass spectrometer works best with this amount ofcarbon). From BP1 to BP6, where a sufficient amount of cobalt + graphite was obtained, 2 fractions weremeasured. The fraction put into tin cups is given in table 2.1. The 13C-values are given in per mil withrespect to the standard Vienna Pee Dee Belemnite (VPDB). As a reference, also 3 samples of untreatedgraphite were measured in the mass spectrometer. The mean values for the sample size and for the 13C-content are given in the bottom line of table 2.1. As a first result, one can say that fractionation takes placeduring combustion and graphitisation, and that the fractionation effect grows with decreasing sample size.For BP8, no 13C value is given, because the mass spectrometer reported a carbon mass of 0.001 mg for thissample. 0.001 mg carbon correspond to only 1.1% of the initial sample mass. BP2 seems to have gainedmass through the combustion/graphitisation process, but this is not necessarily a sign for CO2 coming intothe sample from outside. It is probably only due to measurement uncertanties: MC after combustion ismeasured via CO2 pressure, while MC before combustion weighed with scales. The table shows that thecombustion/graphitisation process always introduces fractionation. As a general rule, one can say that thefractionation effect grows with decreasing sample size. BP4 seems to be an exception from that rule becauseit has very high fractionation but average sample size. An explanation for the unusually high fractionationcould be the big difference in carbon mass before and after combustion: all processes that do not reachcompletion bear a risk for fractionation.

Another problem with the smaller samples is apparently the incomplete combustion. From samples BP7and BP8, only an amount of CO2 that corresponds to respectively 38% and 15% could be gained, althoughall samples BP1 to BP8 were combusted in the same way. These problems could be connected with the badcombustion characteristics of pure graphite. One attempt to enhance the combustion was to lengthen thecombustion time. Therefore, two sets of samples from the standard material GelA (a laboratory workingstandard for 13C and 15N that has been calibrated against several international standards) in different sizeswere combusted. The combustion time was one hour for set 1 (odd sample IDs) and three hours for set 2(even sample IDs; see table 2.2).

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(a) Small reactors (b) Small reactor

(c) Small reactor with Peltier cooling element (d) Small reactor with Peltier cooling element and oven

Figure 2.2: The part of the graphitisation system with small reactors.

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Table 2.1: Combustion and graphitisation of graphite

ID MC [ mg] MC [ mg] MCo[ mg] MCo+C [µ g] δ13C [h]before after Into VPDB

combustion MassSpec

BP1 1.05 0.85 0.79 183 -27.02175 -27.07

BP2 0.81 0.82 0.75 200 -27.06189 -27.08

BP3 0.60 0.52 0.84 244 -27.82247 -27.80

BP4 0.48 0.31 0.89 277 -29.86273 -29.55

BP5 0.42 0.40 0.85 293 -27.83304 -27.94

BP6 0.31 0.27 0.82 364 -29.17358 -29.98

BP7 0.21 0.08 0.75 464 -34.37BP8 0.09 0.01 0.90 421 · · ·

Graphite · · · · · · · · · 97 -25.92

Table 2.2: Combustion and graphitisation of Gel A

1 hour combustion 3 hours combustionID Mass (mg) Yield (%) ID Mass (mg) Combustion yield (%)BP9 0.33 47.7 BP10 0.30 46.9BP11 0.68 43.7 BP12 0.62 35.1BP13 0.87 43.4 BP14 0.92 40.8BP15 1.16 43.6 BP16 1.16 44.4BP17 1.49 38.0 BP18 1.54 37.3

Average 43.3±1.7 Average 40.9±2.2

As can be seen from table 2.2, the average yield does not change significantly with longer combustiontime. Therefore, the normal combustion time of one hour could be applied to all following samples.

It is assumed that if the combustion process would introduce fractionation, it would affect small samplesmore than bigger ones. To test this, normally combusted samples have been compared with samples thatwere made by combusting the double sample size and then splitting up the CO2 gas into two samples. Withthis procedure, it is possible to examine only the size-dependent fractionation from combustion. Graphitisedsamples of the same size are compared, where some of them came from combusted doublets and some fromsingle combustion. The graphitisation took place with cobalt as catalyst. In table 2.3 the delta13C values ofthe singly combusted samples are compared with those of the doublets. This examination is important forthe choice of standard material preparation. If there is no difference between single and doublet combustion,standards can be combusted in great amounts and split up for graphitisation to produce small standardswhich are needed for the measurement of small samples. If there is a difference, then the combustionof standards of the same size as the samples is necessary. The δ13C values for the graphitisation doublets

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BP23/24, BP25/26 and BP27/28 and thus the fractionation does not differ significantly between the aliquotsof one doublet. It can be seen, though, that there is a big difference in the δ13C values between the doublets.Varying fractionation is thus suspected to originate from the combustion process. If the graphitisation wasthe cause for random fractionation, the δ13C values of two samples of a doublet would not agree as theydo here. When comparing the δ13C values of the doublets with those of the single-combustion samples,a tendency towards bigger fractionation can be seen with the single combustion samples, but only if thedoublet BP25/26 and the two last results from BP21/22 are regarded as outliers. Because a clear tendencycan not be observed, further tests are necessary to decide whether the combustion really is the biggest sourceof contamination and fractionation and whether standards can be combusted in big amounts and split upfor graphitisation. Tests are planned using not only doublets, but also quartets, and these tests are plannedto be repeated several times to find a statistically significant answer.

Table 2.3: Single and double combustion and graphitisation of GelA. Samples with similar carbon mass thatare to be compared are grouped by horizontal lines.

Single combustion Double combustionID Mass Combustion δ13C ID Mass Combustion δ13C

(mg GelA) yield (%) (VPDB) (mg GelA) yield (%) (VPDB)BP21/22 0.79 50.1 -30.73 BP29 0.43 -27.32

-26.71-26.80

BP23/24 0.60 40.1 -27.95 BP9 0.33 47.7 -28.28-28.53 BP43 0.33 52.4 -29.51

BP30 0.30 43.2 -30.43BP10 0.30 46.8 -30.80

BP25/26 0.43 46.1 -30.14 BP39 (Fe) 0.28 47.1 -27.53-31.00 BP35 (Fe) 0.21 57.2 -27.38

BP27/28 0.21 43.9 -26.52 BP41 (Fe) 0.16 51.0 -34.56-27.36 BP36 (Fe) 0.09 64.5 -24.49

BP42 (Fe) 0.06 67.8 -30.83

Santos, Southon, Griffin, Beaupre, and Druffel (2007) developed some improvements in the sample prepa-ration process for reducing the sample size. As for the dating of small samples, also small standards areneeded, they compared the combustion of small standards with the combustion of big standards which weredevided into smaller samples for graphitisation. Because there were no differences between standards pre-pared in the two different ways and because it is almost impossible to weigh out so small amounts of standardmaterial, they decided to use big amounts for combustion and to devide them for graphitisation.

After these first tests it was examined if iron is a better catalyst for small samples. Now, cobalt is usedas a catalyst for graphitisation. Several tests have now been done to compare the cobalt with iron andto decide which catalyst is best suited for the graphitisation of small samples. The cobalt powder used inthe laboratory is a spherical cobalt powder, -325 mesh (<45 microns), from Johnson Matthey GmbH AlfaProducts (article no. 00739, manufacturing ceased). The iron I tested is iron reduced, grain size 10 micron,from Merck KGaA (article no. 3819).

The purity, in terms of absence of carbon contamination, as well as the behaviour of a catalyst have tobe tested. Santos, Mazon, Southon, Rifai, and Moore (2007) give 5 criteria for testing catalysts:

1. 12C+ current from pure catalyst in target (that indicates the amount of carbon contamination)2. blank values for coal (measurements of the 14C amount in 14C-dead charcoal targets indicate the

amount of modern carbon contamination)3. conversion time CO2 to graphite

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(a) Pressure in reaction tube (b) Pressure in reaction tube in % of start pressure

Figure 2.3: Graphitisation of two identically sized samples with cobalt and iron as catalyst.

4. homogeneity and lack of sintering5. 12C+ beam current intensity produced from the graphite targets

Testing the first criterion is difficult because it is hard to see the difference between carbon ions that comefrom the catalyst itself and carbon ions originating from the target holder or the ion source (pers. commentKlaus Bahner 2007). Due to several problems with ion source and accelerator, the second and fifth criterioncould neither be tested. The samples are prepared and ready for measurement, but unfortunately, the newion source was not ready for routine measurements before this thesis had to be finished.A first assessmentof catalyst has thus to be based solely on graphitisation ratio and catalyst / graphite structure.

The graphitisation process has been monitored with reading out the pressure sensors. The pressuresensors of the normal-sized reactors are not connected to a computer so that the pressures had to be writtendown manually. Therefore, not the whole nighttime-process could be monitored. Anyway, the first threehours of graphitisation show interesting differences between cobalt and iron catalysts.

In general, it can be concluded that iron is the better catalyst in terms of reaction speed. Normally, thereaction with iron starts soon after the ovens have been switched on, whereas it takes some time for a reactionwith cobalt to begin. Santos, Mazon, Southon, Rifai, and Moore (2007) even observe graphitisation times assmall as 120 minutes for some iron catalysts and sample sizes around 1 mg. In figure 2.3, the graphitisation oftwo samples with the same size, 1.17 mgC, in normal-sized reactors is shown. It can be seen that the reactionfor the sample graphitised on iron is finished after about three hours. At that time, the total pressure forthe reaction with cobalt is only reduced to the half. The final graphite yield after equation 2.2 is 1.03 for thesample graphitised on iron and 0.99 for the sample graphitised on cobalt (SSID 24100). For another sampleof equal size which also was graphitised on cobalt (SSID 24101), the graphite yield is 1.04. A difference inyield for normal-sized samples can therefore not been found.

Figure 2.4 shows the start of a reaction more precisely. It can clearly be seen that the reaction startsimmediately for the two samples graphitised on iron (in R14 and R15). The pressure in the reaction tubesfilled with cobalt, though, rises during the first 10 to 15 minutes of the reaction. After that, the beginninggraphitisation can be seen, but the pressure decreases with a slower rate than in the case of iron catalyst.

Because a fast reaction reduces the risk of contamination, iron was used for the graphitisation of some ofthe samples from Schlamersdorf and Kayhude (see section 4). Because they are normalized using standardsand backgrounds of the same size that were also graphitised using iron, no significant differences are expectedbetween the 14C age measurements of the samples graphitised with cobalt and those graphitised with iron.Therefore, the results remain comparable.

A mass-dependence of the reaction ratio and graphite yield could be observed for graphitisations withiron (see figure 2.5).

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Figure 2.4: The beginning graphitisation of normal-sized samples. In R10 to R13, Co was used as a catalyst,whereas Fe was used in R14 and R15. Pressures in fraction of the maximum pressure.

Figure 2.5: Graphitisation of samples of different sizes with iron. Pressures as fraction of maximum pressure.

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The catalyst amount also seems to play a role in the graphitisation process. Smith, Petrenko, Hua,Southon, and Brailsford (2007) observed that increasing the catalyst amount from 1 mg to 4 mg improvedeither yield or reaction rate, but not both. With a bigger catalyst amount, the life time of the sample inthe ion source is bigger but the current is smaller. They also examined the influence of the method of waterremoval. They conclude that water removal is critical for graphitisation of small samples, but does not affectlarger samples. The reason why water vapor removal is critical for small samples is the following: For asmall sample, there is always a fresh catalyst surface available so that also the reverse action of graphitisationcomes into play (from the right-hand side to the left-hand side in the two following reactions).

CO2 + H2 ↔ CO + H2O (2.5)

CO + H2 ↔ C + H2O (2.6)

When the water vapor is efficiently removed, then these reactions are forced to the right-hand side.An effective water vapor removal depends strongly on the temperature of the water trap if the water

vapor is meant to be frozen to ice. The reason for this is the strong dependence of the vapor pressure of iceon temperature: 12.84 Pa at -40◦C and only 0.06 Pa at -80◦C. It could therefore be interesting to exchangethe existing peltier elements which cool down to about -40◦C with a mixture of dry ice and ethanol which hasa temperature of approximately -80◦C. Another possibility of water vapor removal which is worth trying isthe use of a dessicant like magnesium perchlorate (Mg(ClO4)2). The aqueous vapor pressure over water-free(“anhydrous”) magnesium perchlorate is <0.075 Pa (Smith, Petrenko, Hua, Southon, and Brailsford 2007).With the small amounts of water that are formed during the graphitisation “it is fair to assume” that thewater vapor pressure not rises above approximately 1 Pa. This method of water vapor removal was also usedby Santos, Southon, Griffin, Beaupre, and Druffel (2007) who achieved graphitisation times under 2 hoursand were able to graphitise and “reliably” date samples as small as 0.002 mgC using magnesium perchloratewater traps.

One exception from the general rule that iron is better suited as catalyst is the graphitisation of watersamples. It is well known that it is harder to convert the CO2 extracted from water samples to graphitethan is the case for other types of samples. With water samples, it could be observed, that cobalt is abetter catalyst than iron. The reason for this could be that iron, which is more reactive with regard toCO2, is also more reactive with regard to the other gases which accompany the CO2 extracted from watersamples. When so the surface of the iron is covered with those other gases, there is less surface left on whichthe CO2 could react. In contrast to this, the surface of the less reactive cobalt stays free longer until thereaction temperature is reached and the CO2 starts being reduced to graphite. Another reason could be thehigher content of water vapor that still accompanies the CO2 sample so that it is harder to force the abovereactions to the right-hand side. Figure 2.6 shows the graphitisation of water samples. The samples in thenormal-sized reactor R13 and in the small reactor R110 were graphitised on iron.

SEM microscope pictures of catalyst and graphite

For comparing the catalysing properties of both iron and cobalt, graphitisations with these two materials weredone and the end products compared under the SEM (scanning electron microscope) with a magnification ofup to 20,000. The magnetic properties of the examined material made further magnification impossible: Thestrong magnetic field at the lens would have attracted the sample material so that it would have adhered tothe lens.

On samples BP31, BP32, BP 37 and BP38, both stable isotope measurements and scanning electronmicroscopy were conducted. Figure 2.7 shows them 20,000 times magnified. BP31 and BP32 had beengraphitised with cobalt whereas iron had been used for BP37 and BP38. As the material (graphite + catalyst)was not completely homogenous, it was not clear which carbon concentrations stayed on the catalyst thatwas put in a tin cup for EA C/N measurements or on the catalyst that was used for scanning electronmicroscopy. Therefore, the carbon content of the C/N samples varies a lot: from 38.3% for sample BP31ato 4.7% for sample BP38 (see table 2.4). This difference in graphite content can also be seen on the SEMpictures as will be explained later.

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Figure 2.6: Graphitisation of water samples with cobalt and iron as catalysts. Pressures in % of the maximumpressure.

When taking the SEM pictures, it was paid attention to choosing a representative part of the sample.Figure 2.7 shows SEM pictures of the four above mentioned samples. The difference between cobalt (2.7a andb) and graphite (2.7c and d) can clearly be seen. Cobalt consists of smaller, irregular pieces with no visiblesurface structure. Iron consists of bigger, spherical parts with spiral-like surface patterns. The spheres oftenare connected with each other and form longer chains. This observation fits well to the laboratory experiencewith cobalt and iron as catalysts for graphitisation. When the sample (catalyst + adhering graphite) is beingpressed into a cathode, it can be felt that cobalt has a loose, powderlike structure while iron tends to beharder to form and often sticks together as one piece.

In figure 2.7a, almost only the pure cobalt is visible. In 2.7b, little flakes of graphite have developed onthe cobalt grains. 2.7c shows iron catalysts with a lot of graphite. Note that graphite filaments are visiblearound the graphite flakes that developed on the iron powder. The slightly lighter parts which are visibleon the tips of the graphite filaments are interpreted by Santos, Mazon, Southon, Rifai, and Moore (2007) assmall catalyst particles. In figure 2.7d, only a little bit of graphite has developed on the iron. It is believedthat the surface of catalyst particles is transformed to iron carbide (Fe3C) before graphite filaments grow.It is therefore possible that the sample sizes were not big enough for some samples to allow the beginning offilament growth and that instead most of the carbon was taken up by the catalyst to form iron carbide.

The observed inhomogeneity of the samples shows that it is necessary to be careful to press the wholesample into a cathode. If a little bit of the sample is not pressed into a cathode, it could be that the partwith most graphite gets lost.

2.2.2 Establishing a new graphitisation system with smaller reactors

In order to reduce the reaction volume, thinner quartz tubes and smaller fittings have been installed. Thetotal reaction volume for normal-sized samples is 4.5 cm3 while the new design provides a reaction volumeof 0.8 cm3, which is only about 18 % of the volume for normal-sized samples. It is expected that reactionrates for small samples are better in the smaller volumes, because the pressure is 5.6 times as high as in the

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(a) BP31 (cobalt) (b) BP32 (cobalt)

(c) BP37 (iron) (d) BP38 (iron)

Figure 2.7: SEM pictures of graphitised samples. Note that all pictures are taken with the same magnifica-tion.

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Table 2.4: Graphitised samples for C/N measurements and SEM

Sample Sample material Catalyst mgC C% δ13C [h] SEM pictureBP31a 0.2 mg Graphite 0.9 mg Co 0.13 38.3 -16.16 2.7aBP31b ” ” 0.07 17.3 -31.06 ”BP32 0.48 mg GelA 0.8 mg Co 0.09 16.9 -26.77 2.7bBP37 0.91 mg GelA 0.8 mg Fe 0.146 25.3 -23.18 2.7cBP38 0.36 mg GelA 1.9 mg Fe 0.044 4.7 -22.36 2.7d

normal volumes after the ideal gas law

p =nRTV

with the amount of substance n and the gas constant R. (2.7)

That augments the collision rate between CO2 and H2 and so the reaction probability. A shorter reactiontime reduces the risk of contamination, as for example through air leaks (Smith, Petrenko, Hua, Southon, andBrailsford 2007). Small reactors make it possible to graphitise samples which are too small to be graphitisedin the big reactors. When the sample size is too small, a reaction does not start because of the low pressure.Santos, Southon, Griffin, Beaupre, and Druffel (2007) could reduce the minimum sample size from 0.006to 0.002 mgC with reducing the reactor volume from 3.1 to 1.6 cm3. They also noted that fractionationis smaller when small samples are graphitised in the small reactors. Because of the smaller volume, themaximum sample size for samples being graphitised in the small reactors is 0.2 mgC. Bigger samples wouldcause higher pressures (note that H2 is added with at least 2.1 times the pressure of the CO2 in the reactor)which could cause the reactors to crack, especially when the ovens start heating and expand the gases. Forcomparing the reaction time of small samples graphitised in small and normal-sized reactors, seven sampleswith sizes between 0.09 and 0.18 mgC were graphitised. In figure 2.8, the pressures monitored during thegraphitisation are shown. They are only given as fraction of maximum pressure because the pressure for thesame amount of gas is bigger in the smaller than in the normal reactors so that a comparison only is possiblewith the relative pressure changes. All samples were graphitised using iron catalyst. The reactions werefinished after not more than two hours. The graphitisation yields for this reaction are given in table 2.5.

Table 2.5: Graphitisation yield of small samples

Reactor Sub sample ID mgC Graphite yield (after equation 2.2)R11 24089 0.18 0.97R12 24094 0.07 0.93R13 24095 0.18 0.97R16 24096 0.18 0.98R17 24097 0.15 0.97R19 24098 0.09 1.27R110 24099 0.17 1.15

The calculated graphitisation yield for R19 and R110 is surprisingly high, but this is due to a measurementerror. The pressure transducers for R19 and R110 could not be zeroed so that an offset had to be substractedby hand. Additionally, the zero point changed with time. The changing offset is the reason for incorrectpressure measurements. Still it was possible to monitor the reaction with these pressure transducers becausethe offset changed slowly enough. It can be seen from the pressures in figure 2.8, though, that the completiongrade of the reaction in the small reactors 19 and 110 is bigger than in the normal-sized reactors.

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Figure 2.8: Graphitisation of small samples in normal-sized (R11-R17) and small (R19 and R110) reactors

As was pointed out before, iron is the better catalyst in terms of reaction ratio and graphite yield. Fortesting if the reaction ratio and graphite yield also prove satisfactory for a graphitisation on cobalt underthe same circumstances, two small samples (0.13 and 0.17 mgC) have been graphitised with cobalt in thesmall reactors.

It can be seen in figure 2.9 that the reaction time is around

Figure 2.10: Small sample graphitisationon cobalt.

four hours, which is the double time as for a graphitisation withiron. Smaller reactors alone do thus not shorten the reactiontime so much as does the choice of another catalyst. The cata-lyst plays the stronger role. The graphite yield, though, is thesame for this reaction with cobalt as for the reaction with iron(see above). It is 1.03 for R19 (SSID 24958) and 1.05 for R110(SSID 24958). In figure 2.10, a graphitisation of small samplesis shown for comparing the graphitisation ratio in the big andsmall reactors. It can clearly be seen that the reaction of thesame sample mass (about 0.2 mgC) is faster in a small reactor(R110) than in a big one (R13). But also here, as the sampleswere graphitised using cobalt, the reaction time is quite high:more than four hours for the sample in the small reactor. Thereaction ratio in the normal-sized reactor is even slower: after more than four and a half hours, the pressureis not yet reduced to 50% of the initial pressure. In figure 2.11, the graphitisation yield is shown both for thebig and the small reactors as a function of sample carbon mass. It is clearly visible that the graphite yielddecreases for smaller samples in the big reactors. In small reactors, the graphite yield varies a lot (this isdue to the shifting offset of the measurement apparatus), but appears to be fairly constant and independentof sample mass. The higher yield for smaller sample masses is expected to be an effect of measurement

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(a) Pressure in torr (b) Pressure as fraction of maximum pressure

Figure 2.9: Graphitisation of two small samples in small reactors on cobalt

uncertainty, due to the shifting offset of the pressure transducers.Hua, Jacobsen, Zoppi, Lawson, Williams, Smith, and McGann (2001) also observed a mass-dependence

of yield for samples graphitised with hydrogen in reactors with 3.5 ml using iron as catalyst. The reactiontime was 4 to 8 hours. The yield in their case began to decrease for samples with less than 100 µgCand showed a strong mass-dependence for samples with less than 50 µgC. They observed that for samples<50 µgC, the δ13C value also is mass-dependent. The maximum isotopic fractionation was 14h for samplesof 21 µgC. It has to be kept in mind that fractionation occurs during graphitisation when the reaction doesnot reach completion. A similar mass-dependence for the stable isotope values as for the graphite yieldis therefore expected. Hua, Jacobsen, Zoppi, Lawson, Williams, Smith, and McGann (2001) report thatisotopic fractionation only becomes important for samples <100 µgC. They also measured 14C ratios of the

(a) Big reactors (b) Small reactors

Figure 2.11: Graphitisation yield as a function of sample size for graphitisation on iron and cobalt

processed samples (oxalic acid standards). Even the 13C-corrrected 14C ratios show a mass-dependence forsamples <50 µgC. For the smallest samples, the 14C ratio is only 96% of that of normal sized samples . Thatfact is hard to explain because the measurements were already corrected for fractionation occuring during

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graphitisation, so that it could either be fractionation in the ion source or contamination with 14C depletedcarbon (less than 100 pmC), or a combination of both.

Three effects have to be examined when using the small reactors for routine graphitisation and 14C-dating. The first is the extent of fractionation and is checked by combusting a stable isotope standardmaterial (GelA in this case) and graphitising it in the small reactors. The difference of the δ13C values of thegraphite produced in that way and pure untreated GelA indicates the extent of fractionation. The other twoeffects are contaminations with “modern” and “dead” carbon. As the contamination can come from differentsources with different 14C ages, the total effect is the average of 14C ages of the contaminants, weighted withtheir relative amount. For practical reasons, contaminants are treated mathematically as if coming fromonly two sources: modern and infinitely old carbon. The contribution of the first is estimated by measuring14C-free samples (background samples). The 14C that is measured in a background sample indicates theamount of modern contamination. For estimating the amount of 14C-“dead” carbon contamination, it isassumed that a constant amount of this type of contamination enters the sample. Samples of a standardmaterial in different sizes have to be measured. The differences in 14C ratio between these samples indicatethe amount of 14C-“dead” carbon contamination.

In table 2.6, some results for tests of the extent of fractionation are given. Both big and small reactorswere used, and both Fe and Co were taken as catalyst. The fractionation is defined as the deviation from theδ13C value of untreated GelA, which is -21.81h VPDB. It can clearly be seen that the biggest fractionationis introduced from the graphitisation of a GelA sample in a big reactor on cobalt. The fractionation inthis case is -6.36h. Compared to that, the other two graphitisations with cobalt that took place in smallreactors, introduced less fractionation (-1.12±0.48h in average). The fractionation from graphitisation inbig reactors using iron as catalyst is -2.22±1.72h, so that in this case, the graphitisation with iron introducesless fractionation than the graphitisation with cobalt. The graphitisation with iron in small reactors showssomething completely different: Here, the average fractionation is 0.47±0.88. It is remarkable that thedeviation is positive in this case. A negative deviation from the “true” value means that the heavier isotopesare depleted in the sample so that its δ13C value is more negative than that of the original material. Adepletion in heavier isotopes can easily be explained with incomplete reactions. As it is easier to break12C-O2 bonds than 13C-O2 or 14C-O2 bonds, the lighter isotopes react more readily. It is thus expected thatafter a certain amount of time, a bigger portion of the 12C-O2 is reduced compared to the portion of 13C-O2

or 14C-O2 that is reduced after the same time.

Table 2.6: Quartz tube combustion and graphitisation of GelA samples

Reactor Catalyst Sub sample ID mgC δ13C (VPDB) Fractionationnormal Co 24149 0.20 -28.17 -6.36small Co 24150 0.08 -23.27 -1.46small Co 24151 0.10 -22.59 -0.78normal Fe 24152 0.18 -22.72 -0.91normal Fe 24153 0.07 -25.70 -3.89normal Fe 24154 0.18 -22.09 -0.28normal Fe 24155 0.18 -23.72 -1.91normal Fe 24156 0.15 -25.91 -4.1small Fe 24157 0.05 -21.97 -0.16small Fe 24158 0.09 -20.72 1.09

A positive deviation indicates an enrichment in heavier isotopes. This could happen during the graphiti-sation process when CO is formed (also the dissociation CO2 to produce CO is easier for the lighter carbonisotopes). It is hard to explain, though, why just the graphitisation with iron in small reactors causes en-richment in heavier isotopes. It was expected that the same kind of fractionation (enrichment or depletion)

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occured for all reactors and catalyst types and that only the degree of fractionation varied. As the enrich-ment in heavier isotopes only happened for one sample, a measurement error can not be ruled out. This onepossible outlier and the quite high standard deviations suggest a repetition of these experiments. A biggernumber of samples is desired to ascertain that the type and extent of fractionation really depend on thegraphitisation settings. Although the number of samples was too small to understand the conditions thatinfluence fractionation, a general advice for future sample preparation can be given. The iron catalyst shouldbe preferred, and the samples should be graphitised in small reactors, if the sample size is below 0.2 mgC.As can be seen from the following table, both choices reduce the extent of fractionation:

δ13C mean value of graphite. . . Average fractionation. . . from graphitisation on Co -2.9±1.8h. . . from graphitisation on Fe -1.5±0.7h

. . . from graphitisation in normal-sized reactors -2.9±0.9h. . . from graphitisation in small reactors -0.3±0.5h

It has been shown that using iron as a catalyst and reducing the reaction volume both lead to fastergraphitisation ratios and possibly reduce fractionation. Another possibility of shortening the reaction timewould be another activation method for the catalyst. The standard procedure is 1 hour H2 at 400◦C, butwith a preceding oxygen treatment for 30 minutes, Hua, Zoppi, Williams, and Smith (2004) report to havereduced the graphitisation time to one third. The oxygen step enlarges the surface area of the catalyst andso speeds up the reaction. This method has not yet been applied in our laboratory because the usage ofhydrogen and oxygen in the same system can be dangerous because hydrogen and oxygen together form theexplosive gas oxyhydrogen.

Concluding, a recommendation can be given to use iron instead of cobalt as a catalyst. The mostimportant reason for this choice is the faster reaction ratio of the graphitisation with iron. Another recom-mendation is the use of reactor volumes that are adequate to the sample sizes. The smallest possible reactionvolume should be chosen as this has the potential to reduce fractionation, i.e. leads to better completion ofthe graphitisation reaction.

2.2.3 On-line combustion with EA measurements

After a short description of the existing methods of sample combustion for 14C dating and stable isotopeanalysis, I will explain why development in the existing sample combustion for 14C dating is necessary.The sample combustion at the elemental analyzer for stable isotope measurements will be combined with atrapping device that can trap a fraction of the sample’s CO2. The advantages of this system will be pointedout below. Finally, the results of first tests of this device will be presented.

The AMS 14C laboratory uses a mass spectrometer for 13C measurements because it is more precise thanAMS, and for 18O, 15N, D (2H), and 34S measurements. 13C and 18O measurements are done via a dualinlet (DI) system which uses a Gilson 220XL sampling robot which transfers the CO2 gas from vials in a 50position manifold bed to the mass spectrometer. 13C measurements for correcting fractionation effects for14C datings are also done with this system.

For 15N and 13C measurements, small fractions of sample material (corresponding to 200µgC) are weighedout into tin capsules and combusted at a continuous flow elemental analyzer (CF-EA) which is shown infigure 2.12. The standard combustion of the samples for graphitisation and AMS 14C measurements takesplace in quartz tubes filled with 200 mg copper oxide, which is heated at 900◦C for one hour to burn offpossible contamination. The samples are filled into the prepared quartz tubes, which are then evacuatedand sealed by melting the glass. The samples are combusted for one hour at 900◦C: At temperatures above500◦C, the CuO undergoes pyrolytic decomposition and provides O2 for oxidation (Kirner, Taylor, andSouthon 1995) so that the carbon from the sample has O2 available to react to CO2. The CO2 is thenmanually transferred to the graphitisation system where a fraction corresponding to 1.1 mgC is graphitisedand a small aliquot is saved for 13C analysis and transferred to the mass spectrometer via the DI. If stableisotope analysis (13C and 15N) is desired, another piece of sample has to be weighed out into a tin capsule

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Figure 2.12: The continuous flow elemental analyzer (CF-EA). The sample is combusted in the combustiontube, crosses the chromatograph column and then enters the tube leading to the trapping device and themass spectrometer. After J. Olsen, unpublished PhD thesis, Aarhus University.

and seperately combusted in an continuous flow elemental analyzer (CF-EA). Continuous flow means thata constant flow of helium transports the sample from combustion to mass spectrometer.

Several groups have found out that the combustion process brings the biggest fractionation and con-tamination in the AMS sample preparation process. Vandeputte, Moens, Dams, and van der Plicht (1998)examined the contamination potential of both the copper oxide and the iron they used as a catalyst for graphi-tisation. Although the catalyst may have a higher carbon content than the copper oxide, the contaminationcontribution of the last one prevails. The amount of copper oxide needed for one combustion/graphitisationis about 100 times as big as the amount of catalyst. Pearson, McNichol, Schneider, and von Reden (1998)also report that the biggest contamination, about 1 µgC, is being introduced during the combustion. Thisconstant amount of contamination affects small samples in particular. Additionally, it has been observedthat some kinds of samples are not combusted completely and that it sometimes is hard to place the sampleat the bottom of the glass: often, the samples are electrostatically charged and stick to the walls of the glasstube so that the sample might be affected by the melting process when it is sticking to the upper parts ofthe tube. This also is a problem especially for very small samples where the sample is hardly visible. Theseobservations necessitate developments in the combustion process if smaller samples are to be dated reliably.

The existing combustion system for stable isotope measurements at the continuous flow elemental analyser(CF-EA, see figure 2.12) uses combustion at ca. 1000◦C in an oxygen-enriched atmosphere, where thesamples are burned in tin capsules. The high temperature and oxygen-enriched atmosphere provide forflash combustion of the sample. Through a GC (gas chromatography) column, the nitrogen and othercombustion products are separated from the CO2 and the gases are introduced into the mass spectrometer.The introduction to the mass spectrometer takes place through an open split that reduces the sample sizeto an amount tolerable by the mass spectrometer.

The objective is now to add a device for CO2 trapping to that system so that the CO2 from the samplecombusted in the EA can be transferred to the graphitisation system. The combustion of the sample ina quartz tube is in this case not needed any longer. Such an automatic gas handling system has alreadybeen developed by Jesper Olsen (Olsen, Heinemeier, Bahner, Graney, and Phillips 2007). It is a cryogenictrapping device added in such a way that it is possible to shift between DI applications and CF-EA-AMS

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applications of the Gilson robot. CF-EA-AMS denotes the sample combustion at the EA and the trappingof CO2 for AMS measurements with simultanous stable isotope measurements.

Now instead of two combustions on two aliquots of the same sample material, one for stable isotopemeasurement and one for graphitisation for radiocarbon dating, only one combustion is needed. The time-consuming process of weighing out the sample into a quartz tube, flame-sealing the tube and combustionover night is now not longer necessary. Online combustion combined with stable isotope measurements hasnot only the potential to save time during the preparation process. It can also minimize contamination aseach step in the sample preparation can introduce contamination so that a minimization of preparation stepsis favoured.

The advantage of that combustion method is, besides the reduction of preparation steps, the purenessof the trapped CO2 which makes its transfer to the graphitisation reaction tube easier and which hasthe potential to react faster to graphite than samples combusted in quartz tubes. A combination of thatcombustion system with a gas ion source has been designed at the Oxford Radiocarbon Accelerator Unit,but the limited precision restricts its use to biomedical samples, samples where high precision is not neededor to very small samples (between 30 and 150 µgC) where high precision is not achievable (Bronk Ramseyand Humm 2000).

In some laboratories, the tin capsules are cleaned for example with cyclohexane and acetone in orderto remove any traces of hydrocarbons. Olsen, Heinemeier, Bahner, Graney, and Phillips (2007) combusted0, 1, or 5 empty tin capsules in a quartz tube together with anthracite coal. This process can add about0.2 µg modern carbon to the sample which results in a 0.024 higher pmC. They conclude that for very smallsamples or very old 14C samples a tin cup cleaning procedure may be successfully adopted. It was concludedthat a cleaning procedure is not necessary for our first experiments with the new gas handling system. It isexpected that a contamination corresponding to more than 0.2 µg modern carbon is introduced in the firsttest runs with background samples through leaks in the system or similar sources, so that it would make nodifference to clean the tin capsules before use.

After combustion, the sample is transported on with the continuous helium flow. A small fraction ofthe sample CO2 reaches the mass spectrometer while a bigger fraction passes a quite thick tube which iscooled down with liquid nitrogen. This cooled-down part of the tube is the trap. It can be sealed withcomputer-controlled valves after the whole sample gas has passed and the sample is completely frozen.Before unfreezing the sample, Helium or other gasses that might be present in the trap, but not frozen, arepumped away. After sealing the trap, it is warmed up again so that the CO2 becomes gaseous again. Nowthe pressure in the closed volume can be measured. Once the closed volume is calibrated, the pressure canbe taken as a measure of sample mass.

A Gilson 220XL sampling robot is routinely used for the transfer of CO2 gas from samples that havebeen combusted elsewhere. They are transported in manifold tubes to the mass spectrometer for 13C and18O measurements. This system is for example used for 13C analysis on the CO2 that was combusted forgraphitisation. It is shown in figure 2.13. Now, the same Gilson robot can be used the other way roundfor trapping the samples that were combusted in the EA and transferring the CO2 into manifold tubes totransport it to the graphitisation system. The system designed by J. Olsen used a movable dewar that wasattached to the Gilson robot arm and could be filled automatically with liquid nitrogen. It should thereforehave been possible to run the system automatically. The glas vials that can be used with this automaticaldewar are smaller that the ones normally used for 13C sample transfer. They have a rubber septum and canonly be used one because the septum gets broken when transferring the sample. For transfer of the sample,the needle has to be moved to the respective vial. Then the needle is lowered just so much that it entersthe septum but not penetrates it. It is so possible to pump out the air in the needle and transfer line, as airenters the needle and transfer line when the needle moves. Afterwords the needle can be lowered completelyso that the vial can be evacuated and is ready for sample transfer. The dewar is so moved to the glass vialand filled with liquid nitrogen so that the sample can be frozen into the glass vial. The rubber septum ofthe vial is subject to high stress when the needle is moving through the septum. The septum is thereforedeformed quite a lot. The “seal height”, that is, the position of the needle when it enters the septum withoutpenetrating it, is 2mm deeper for a septum that already was used than for a new, unused one. It is therefore

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(a) The manifold bed and the Gilson 220XL sam-pling robot

(b) Sample transfer from a manifold through theneedle to the mass spectrometer

Figure 2.13: Sample transfer for δ13C dual inlet (DI) measurements

assumed that such a vial only can be used for one sample preparation process. During transfer of the trappedCO2 sample to the graphitisation system, the septum is again subject to strong deformation forces. Anotherdisadvantage with these rubber septa is that rubber can get stucked in the opening of the needle so that theneedle is blocked after some trapping runs. A possible solution could be another needle with a side hole.It is therefore planned for the future to find a suitable needle that has a side hole but is sharp enough topenetrate the rubber septum without deforming it too much. For the tests described here, the same manifoldtubes that are used for dual inlet 13C measurements were utilised. The advantage of them is that they havea valve instead of a rubber septum so that they can be used numerous times without the danger of leaks. Itis furthermore easier to transfer the samples from these manifold tubes to the graphitisation system.

Olsen, Heinemeier, Bahner, Graney, and Phillips (2007) report a trapping efficiency of 38% to 84% whenthe system is running automatically, but 97% when dewar and needle are moved by hand. Their measurementresults are promising: “The elemental composition of carbon and nitrogen and the stable isotope analysisof δ13C and δ15N perfectly match the result expected for normal CF-EA analysis” and “the δ13C valuesdetermined by the CF-EA-AMS and the DI method on the same CO2 gas all mutually agree, indicating thatisotopic fractionation by splitting of the CO2 gas is insignificant”.

There was one disadvantage with the system described above. That is that the amount of CO2 trapped inthe glass vials was totally unknown. Besides trapping, it is also important to measure the amount of trappedCO2. Therefore further developments of the gas handling system had to be done. The system developedby J. Olsen was therefore modified for making it possible to check the trapped amount of CO2. A “trap”was constructed and built in so that the sample after combustion could be trapped and its amount could bemeasured before it was transferred to the graphitisation system (see figure 2.14). Air-actuated valves thatare controlled by the mass spectrometer computer are used for realizing this trapping system, see figure 2.15.The 4 port valve can switch between two positions. In the first one, the gas from the EA passes through thetrap. In the second position, the trap is isolated so that gas coming from the EA is directly lead to vent.The physical realisation of the trap is a small copper tank that can be filled with liquid nitrogen using a

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Figure 2.14: A sketch of the device for trapping CO2 from EA combustion. After the amount of CO2 ismeausered, the CO2 is via the existing parts of the dual inlet / Gilson transferred to a manifold tube.

pressure air pump. This pump is also controlled by the mass spectrometer computer. The actual trap is astainless steel tube that is wrapped around this tank. For heating the trap after trapping, a heating wire isalso wrapped around the copper tank. The trapping yield for the modified system is given in table 2.7.

As the object is to trap samples for 14C dating, the fractionation and contamination introduced duringthe trapping procedure have to be estimated. The fractionation can be examined with the combustion andtrapping of isotopic standards. In this case, the laboratory standard GelA is used. It has a carbon contentof 46% and its δ13C value is -21.81h. The difference in δ13C between the obtained graphite and the originalmaterial indicates the extent of fractionation. This extent of fractionation has to be compared with thefractionation that is introduced during the normal sample combustion in quartz tubes. The new combustionand trapping method can be used for routine sample preparation if it does not induce a higher degree offractionation than the “traditional” method. The extent of modern, that is 14C containing, contamination isassessed by the preparation of 14C-free samples. If those background samples have a 14C age comparable tothat of other background samples prepared with other methods, then the trapping procedure is good enoughto be used for the preparation of old samples. For estimating the amount of old, 14C-free, contamination, 14C-containing samples of different sizes are dated. From the observed mass-dependence of 14C concentration,the amount of 14C-free contamination can be estimated.

Some GelA and background anthracite coal samples were combusted in the EA and trapped in themodified trapping device. Both groups of samples were graphitised. The graphite-catalyst mixture obtainedfrom GelA was placed into tin capsules for EA measurement. The difference between the measured δ13Cvalue for pure GelA samples and the δ13C value for combusted and graphitised GelA samples defined asthe fractionation. The graphite-catalyst mixture obtained from 14C-“dead” anthracite coal was pressed intocathodes for 14C dating. For comparison, some GelA samples were converted to graphite in the “traditional”way, i.e. combusted in quartz tubes and graphitised. The results of the “traditional” combustion are givenin table 2.6 Figure 2.16 shows the δ13C values for these GelA graphite samples. They were combusted inquartz tubes, graphitised and then 13C-measured using CF-EA mass spectrometry. 2.16a and b shows theδ13C values of 10 GelA samples as a function of sample mass (in mgC). The GelA samples were combusted inqartz tubes and graphitised with iron or cobalt in big (4.5 cm3) or small (0.8 cm3) reactors. In figure 2.16a,

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Figure 2.15: The valves that control the trapping process

big reactors are marked with red and small reactors with blue squares. In figure 2.16b, samples that weregraphitised using cobalt as catalyst are marked with red and those graphitised with iron with blue squares.

The valves we used for the first tests of the trapping device were not “vacuum-tight” enough for thelow pressures in the system. Therefore, new valves were installed and the volume of the tubes and fittingsaround the trap was reduced. Unfortunately, it took a long time until tight connections to the valves werefinished in the workshop. When this finally was achieved, one of the new valves itself proved to have a leak.The long delivery time of these valves made it impossible to rebuild and test the trapping device completely.The tests above the horizontal line in table 2.7 were done with the setup shown above, with the valves thatwere not vacuum tight. The tests under the horizontal line were done after the new valves were installedand the volume of the tubes and fittings was reduced.

As can be seen from this table, the trapping efficiency varies a lot. This is partly due to different problemsthat occured during trapping tests and necessitated modifications of the system, as for example valves thatwere not completely vacuum-tight. Here, the δ13C measurement results for some GelA samples that werecombusted in the EA, trapped, and graphitised, are given.

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(a) Quartz tube combustion - comparison big and smallreactors

(b) Quartz tube combustion - comparison cobalt and ironcatalyst

Figure 2.16: Combustion and graphitisation of GelA - comparison between different graphitisation parame-ters after “traditionel” combustion in quartz tubes

Table 2.7: CO2 trapping tests. The sample is filled into a tin capsule and combusted at the EA. The samplesize in mgC is calculated from the sample size and the carbon content of the respective sample type: 90% forthe background material Anthracite charcoal and 46% for the stable isotope working standard GelA. Thetrapped amount of CO2 was obtained by measuring the pressure of the CO2 in a calibrated volume.

Sample material Sample size (mg) Sample size (mgC) Trapped (mgC) Trapping efficiencyAnthracite 0.23 0.21 0.20 95%Anthracite 0.39 0.35 0.30 86%Anthracite 0.80 0.72 0.50 69%Anthracite 1.34 1.21 0.63 52%GelA 2.40 1.10 0.36 35%GelA 2.70 1.24 0.28 23%GelA 1.41 0.65 0.16 25%GelA 2.07 0.95 0.15 16%GelA 0.86 0.40 0.09 23%Anthracite 0.49 0.44 0.28 64%Anthracite 1.04 0.94 0.29 31%GelA 1.12 0.52 0.45 87%Anthracite 0.49 0.44 0.28 64%Anthracite 1.04 0.94 0.29 31%GelA 1.12 0.52 0.45 87%GelA 1.02 0.47 0.23 49%GelA 0.75 0.35 0.19 54%GelA 0.41 0.19 0.08 42%GelA 1.02 0.47 0.27 57%GelA 0.86 0.40 0.27 68%

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SSID trap yield trapped reactor δ13C fractionationCO2 (mgC) type (hVPDB) (hVPDB)

27520 87% 0.45 big -23.11±0.10 -1.3027521 87% 0.45 big -23.18±0.10 -1.3727522 49% 0.23 big -22.82±0.10 -1.0127523 54% 0.19 small -21.62±0.10 0.1927524 42% 0.08 small -22.91±0.10 -1.1027525 57% 0.27 big -34.78±0.10 -12.9727526 68% 0.27 big -35.88±0.10 -14.07

Apparently, the CO2 gas that was trapped and graphitised originates from GelA. Otherwise, it wouldhave totally different δ13C values. The fractionation, which is the deviation from the δ13C value -21.81hofuntreated GelA, is now compared between the samples combusted and trapped at the EA and the samplescombusted “traditionally”. The δ13C values of the samples from traditional combustion can be found intable2.6. It is striking that the fractionation value is smaller for the trapped samples than for the traditionallycombusted ones. For better comparison, the results already presented in table 2.2.2 are given here again.

δ13C mean value of graphite. . . Average fractionation. . . from graphitisation on Co -2.9±1.8h. . . from graphitisation on Fe -1.5±0.7h

. . . from graphitisation in normal-sized reactors -2.9±0.9h. . . from graphitisation in small reactors -0.3±0.5h

It can be seen that even the biggest fractionation in a trapped sample, a deviation of -1.37hfrom theGelA value, is smaller than the fractionation in most cases of traditional combustion and graphitisation.The trap test samples were graphitised on iron and according to their size in big or small reactors.

The contamination with modern carbon was planned to be tested with the EA combustion, trapping,graphitisation and 14C dating of anthracite samples. The anthracite is assumed to be 14C-free. For findingout how big the amount of modern carbon is that is introduced during AMS measurement, 14C-“dead”samples are routinely dated between the dating of unknown samples. The amount of modern carbon thatis introduced during the combustion and trapping procedure is calculated with substracting the normalAMS background pmC from the anthracite sample’s pmC. Unfortunately, the results of this test are not yetavailable. It was planned that the samples should be measured in the new ion source. Therefore, also smallsample sizes and iron as catalyst were used. Unfortunately, the new ion source was not yet runnning. Dueto different practical problems, it was neither possible to test the last aspect, that is, the contamination withold carbon from the EA and trapping device. For estimating the amount of 14C-“dead” carbon introducedduring the trapping procedure, one had to combust and 14C-date standard samples of different sizes whichhave a 14C activity well above background level, as mentioned above. The pmC-difference between normal-sized and small samples is an indicator for the amount of 14C-“dead” carbon that enters all the samples,assuming that the amount of old carbon introduced in the trapping procedure is independent of sample size.This test is planned to be made in the future after several problem have delayed the assembling and testing ofthe trapping device. It is also planned for future tests to measure the δ13C value of the combusted or trappedgas via dual inlet mass spectronomy. This would enable us to estimate the influence of the graphitisation,when the δ13C of the gas are compared to those of the graphite. The limited time and limited amount ofsamples made it impossible to measure δ13C with both methods. Therefore, only the graphite was examined,as the intention to develop such a trapping system is the preparation of CO2 samples for graphitisation andAMS measurements.

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Chapter 3

The sites

The aim of this thesis is, as mentioned before, dating the first occurrence of pottery in Northern Germanywhich at that time was inhabited by the Late Mesolithic Ertebølle culture, a culture of hunters and gatherers.The emergence of pottery in Northern Germany is on the one hand an important indicator for contacts toother European groups already using pottery. On the other hand, pottery is one of the characteristics of theNeolithic, thus indicating the beginning transition from a hunter-gatherer to an agricultural society.

Ertebølle inland sites in Schleswig-Holstein play an important role in archaeology because most coastalsites are inaccessible due to the rising of sea levels (Hartz (1997); see section 3.3.2). Two inland sites next tohardwater rivers were chosen for further examination: Schlamersdorf and Kayhude. The radiocarbon datesof foodcrusts on pottery from these sites showed higher ages than those from coastal sites, although the sameage for both categories of settlements had been expected. The food crusts were dated to 5400 BC for Kayhudeand 5200 BC for Schlamersdorf (pers. comment Hartz 2007), see figure 3.1 on page 57. The pottery datesare the oldest evidence for pottery in Schleswig-Holstein. Pottery from coastal sites in Schleswig-Holsteinis not older than 4750 BC (Hartz and Lubke 2006). In Denmark, pottery does not occur before 4600 BCalthough Denmark was inhabited by the people of the same culture (Hartz 1996). One possible explanation– if it should not be the hardwater effect – is the close contact between southern Schleswig-Holstein and theNeolithic regions south of the river Elbe.

The two sites regarded here have been shortly occupied hunting sites from the Ertebølle culture. A shortoccupation time of a settlement site can be derived from different findings, including the presence of flintartefacts while there is no indication for flint knapping or the absence of pollen of settlement indicators likeribwort plantain or sorrel.

In this chapter, I will describe the two sites from which samples have been taken for radiocarbon anal-ysis. I will explain the archaeological background in some detail to facilitate the later interpretation of theexperimental results. A description of the sites and their archaeological classification follows as well as aportrayal of the culture of that time. First, the geography and research history will be described. Afterthat, the geology of the sites will be addressed and the probablility of a hardwater effect will be estimated.Therafter, the archaeological culture that is concerned here will be characterized by the natural environmentto which it was adapted to by its economy (i.e. substistence strategies) and artefacts. An assessment of theexisting theories regarding the transition from a hunter-gatherer to a farming society will be presented insection 3.3.5.

3.1 Geography and research history

The site at Schlamersdorf (district Stormarn, see figure 3.2) is located about 7 km north west of Bad Oldesloein the valley of the river Trave, in a valley section which is 2 km long and 700 m wide and narrows to thenorth and south to 200 m. The site regarded here, with the official name Schlamersdorf LA 5 (in the followingsimply called Schlamersdorf), is situated on a low spit of land about 7.5 m above sea level (Hartz 1997) that

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Figure 3.1: Map of Kayhude, Schlamersdorf and other EBK sites with appendant food crust datings.

reached into the former lake or river system. The Trave is the biggest river of Schleswig-Holstein that flowsinto the baltic sea (Ministerium fur Umwelt, Naturschutz und Landwirtschaft des Landes Schleswig-Holstein2003).

Already in the 1930s, stone age artefacts were found 3 km northwest of Schlamersdorf when the Trave wasstraightened on a stretch of 350 m. The straightened part of the river with the bayou west of it can be seenon figure 3.2. The finds, different antler and flint artefacts and potsherds, belonged to the Ertebølle culture.In 1985, K. Bokelman and S. Hartz tried to find the settlement site where these finds came from, and in1986-1989, a total area of 400 m2 was excavated, not only for reconstructing the situation at the settlement,but also for reconstructing the development of the lake/river which now is the Trave (Hartz 1997).

At Schlamersdorf, there are two sites called LA5 and LA15 (LA as abbreviation of “Landesaufnahme”)which were excavated in 1986-1990 in the course of the project “Neolithisation in Schleswig-Holstein” of theDFG (Deutsche Forschungsgemeinschaft, German Research Association). About 3,500 flint artefacts wereexcavated, furthermore 800 potsherds, 400 unworked bones and antler fragments, three antler tools, onesandstone axe, some wooden stakes that were rammed in the lake ground, and a lot of burnt flint and potboilers (Hartz 1996).

Kayhude (district Segeberg, see figure 3.3) is situated 15 km north of Hamburg next to the river Alsterthat flows into the river Elbe in Hamburg. The site is situated in a narrow flood plain (about 50 m wide)with geest ridges on both sides of the Alster. North of the site there is the fen “Wakendorfer Moor”, to the

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Figure 3.2: A map of the site Schlamersdorf LA 5 (upper left) and its surroundings

south the “Niendorfer Moor”. Both fens are likely to be former lakes.During river regulation works, a big amount of organic finds was dug up from the fluvial sediments. The

site was characterized by a lot of mesolithic surface finds (Clausen 2007). It was excavated in 2005/2006 bySchleswig-Holstein’s state office for archaeology (“Archaologisches Landesamt”) on an area of 80 m2. 1500finds could be excavated of which about 70 were potsherds. All find material came from the waste zone inopen water. Pollen analysis showed that the site was in a shallow water region which slowly sedimented.The Alster at that time was about 50 m wide and often changed its riverbed (pers. comment Ingo Clausen2007). A 8 m long row of wooden poles with a length of up to 70 cm can be interpreted as a fish weir.According to 14C datings, it was constructed around 5000 BC. Other finds were antler axes (among themseveral T-axes), typical Ertebølle pottery, wooden tools, a stone mace head, pot boilers and several boneand antler remains from wild animals (Clausen 2007). One date of a foodcrust on a potsherd gave the age5400 BC, which is 400 years older than the fish weir and almost 800 years older than pottery from coastalsites (Clausen 2007).

Layers of sand and detritus were washed ashore and had influence on the finds of the upper layers. Someof the finds are positioned diagonally or upright in the sand so it can be concluded that they have been movedby the water. Because of the different layers which were washed ashore, it is hard to draw a stratigraphy.It is thus hard to conclude which of the artefacts were associated. Therefore, only finds from a stone layerat the bottom of all the layers were taken. This stone layer seemed to be undisturbed and contained two

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Figure 3.3: A map of the site Kayhude LA8 (marked with yellow in the center of the map) and its surroundings

T-axes, a mace head and many ceramic and flint artefacts (pers. comment Ingo Clausen 2007).

3.2 Geology

As explained in section 1.2.3, the water hardness is an indicator for the carbonate concentration in the waterand thus an indicator for the hardwater effect. We assume that the water hardness as we measure it nowhas not much changed from the water hardness during the time of the Ertebølle culture. There are processeswhich can alter the water hardness of a river. The one is changes in the course of the river or decalcificationof the underground. The other is man-made changes of water hardness, for example marling of the fieldsnext to the river so that carbonate from the marl can be washed out into the river. We now have to estimatethe probability of these processes for the rivers Alster and Trave.

Both rivers are supposed to have been fluvial systems with hard water already during the time of thefood crust formation, the Ertebølle period in the late Atlantic pollen zone, and the course of the rivers isexpected to have changed only to a very limited extent. Anthropogenic changes have as well taken place onlyto a limited amount on these rivers: ”The Trave and Oberalster [the upper Alster] are two of the few near-natural brooks and rivers in Schleswig-Holstein and Hamburg” (http://www.uni-kiel.de/Geographie/lehrv-online/GeoVis2000/InternetGIS/Ergebnis/att/Texte.html from 12. July 2007, author’s translation).

There is another possible man-made change of water hardness: the marling of the fields next to the rivers.

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Marl is a loose or crumbling earthy deposit (as of sand, silt, or clay) that contains a substantial amount ofcalcium carbonate (Merriam-Webster Online Dictionary on September 11, 2007) which is applied to muddy,acidic soils. The sand or clay is used to make the ground more compact and the calcium carbonate canneutralize acid to improve conditions for agriculture. So there is a danger that the water hardness increasedduring historical times because the calcium carbonate from the marl could have been washed out into theriver. For the Alster, there is a low possibility for this effect, because people in that region were poorand could probably not afford the marl. Additionally, they mainly lived on selling peat and clay bricks toHamburg, and not on agriculture. For the moderate agriculture in this region, the land did not need tobe used intensively. It is therefore unlikely that expensive marl was used for improving the wet fields nextto the river (pers. comment Ingo Clausen 2007). The region at the Trave around Schlamersdorf was moreprosperous. It has therfore been suspected that great land owners used marl to improve the quality of theirfields. However, there is no reason for that concern: The Trave valley between Bad Oldesloe and Schwissel,including Schlamersdorf, has been thoroughly examined by U. Cimiotti and he excludes this possible sourceof “carbonate contamination”: The lowlands next to the river have been agriculturally so unattractive thatthey have not even been examined before Cimiotti’s work (Cimiotti 1983). The underground of the presentTrave could have changed since the Mesolithic/Neolithic, because it consists mainly of sediments. Still itcan be expected that the Trave had hard water also in former times because the Trave valley is called “oneof the best-preserved examples of subglacial meltwater tunnel valley” with mostly undisturbed landscape(Ministerium fur Umwelt, Naturschutz und Landwirtschaft des Landes Schleswig-Holstein 2003). Duringthe Atlantic period, there was a large body of water in the Trave valley with a slow current. Probably theTrave already ran through this lake system during the Boreal (Cimiotti 1983). In the Atlantic, a strongaggradation of the lake basin started that led to a lowland with fens through which the river Trave wasflowing, surrounded by wetlands. Through the dry phase of the Sub-Boreal, the water level sank and forestsspread along the river, resulting in the formation of peat (“Bruchwaldtorf”) but were drowned again duringthe cool and humid Sub-Atlantic, leading to fens and the formation of fen peat. Today, the Trave valleywould still be dominated by fens if there had not been changes of the landscape through straightening of theriver, drainage and pasturing (Cimiotti 1983). The natural vegetation and appearance of the Trave valleytoday is therefore similar to the situation during the late Atlantic.

3.2.1 Water hardness and 14C in the Trave and Alster

Both rivers show a quite high carbonate content: The Trave downriver of the Wardersee at Warderbruck (ca.25 km upriver of Schlamersdorf) has an average calcium concentration of 87.62±12.29 mg/l and a magnesiumconcentration of 7.19±0.69 mg/l so that the total water hardness, when neglecting other alkaline earth metalions, is 94.81±12.59 mg/l. That corresponds to 13.3±1.8 German degrees (◦dH (0-8.4◦dH: “soft”, 8.4-14◦dH:“medium”, >14◦dH: “hard”)), the unit which is common both in Denmark and in Germany to state thehardness of water. The Alster at the tide gauge Wulksfelde (5 km downriver of Kayhude) has 61.51±9.17 mg/lCa and 5.19±0.57 mg/l Mg. The total water hardness 66.71±9.58 mg/l corresponds to 9.3±1.3◦dH, which isstill a medium hardness. The Ca and Mg concentrations were mean values of the monthly measurements fromthe State Agency for Nature and Environment of Schleswig-Holstein, Germany. For the Trave, measurementshave been done in 1998 and from 1/2001 to 12/2006. The Ca and Mg concentrations of the Alster havebeen measured from 1/1997 to 12/1998 and from 12/2000 to 12/2006 (LANU, pers. comm. 2007). Seesection 1.2.2 for a definition of water hardness and its implications for 14C dating. The water hardness ofthe water samples Trave 1.1 and Alster 1.1 was measured. These were the water samples which were takenclosest to the sites Schlamersdorf and Kayhude, respectively. The Trave water had a hardness of about13◦dH, the Alster water about 10.5◦dH. These values are consistent with the measurement of the StateAgency for Nature and Environment (see above). The relatively high water hardness makes a hardwatereffect on pottery plausible, if people from that time had cooked freshwater fish in the pots. The effect isexpected to be greater at Schlamersdorf, Trave, than at Kayhude, Alster, but the radiocarbon dates nowavailable seem to indicate the opposite (see section 4.2.1 and 4.2.3).

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3.3 Ertebølle and Funnel Beaker culture

The Ertebølle culture (EBK) is named after the “classic kitchenmidden at Ertebølle, a Late Mesolithic coastalsite” (Andersen and Johansen 1986). It is a Mesolithic hunter-gatherer culture with some neolithic habits inSouthern Sweden, Denmark and Northern Germany. Although the coastal kitchenmiddens are a well-knowncharacteristic of the Ertebølle culture, there are also many Ertebølle sites without kitchenmiddens as well asinland sites.

Instead of some neolithic culture specific elements, “such as ceramics

Figure 3.4: Funnel beaker

or polished axes” (Hartz and Lubke 2006), a classification of the EBK intothe Mesolithic stands to reason because the most important criterion for theclassification is the “producing way of life” (Hartz and Lubke 2006). “However,Ertebølle culture has to be differentiated as Nordic Terminal Mesolithic periodfrom the Late Mesolithic, as it was exposed to an acculturation process throughthe neighbouring Central European Neolithic cultures like Linear pottery andPost-Linear pottery cultures. Subsistence economy and settlement types ofthe Nordic Terminal Mesolithic are based on the Late Mesolithic tradition.Only the artefact assemblages allow an archaeo-typological differentiation fromthe Late Mesolithic” (Hartz and Lubke 2006). The Ertebølle culture can besubdivided into two phases: the “aceramic” (before the introduction of pottery) and the “ceramic” phase.Only recent research has assured that the aceramic Ertebølle was present in Northern Germany, while thisphase has been known for a long time in Denmark (Hartz 2005). The Funnel Beaker culture (TRB, theabbreviation for German “Trichterbecher”) is the first completely neolithic culture of the North GermanPlain in the sense of a society whose economy is based on agriculture. The Funnel Beaker culture is namedafter a typical kind of pottery, the funnel beaker (see figure 3.4) and follows the EBK. The sites which areexamined in this thesis belong to the EBK and have probably the oldest pottery in Schleswig-Holstein.

3.3.1 EBK research history and Køkkenmøddinger

In this section, I will describe how the Ertebølle culture was discovered. A description of the site next toErtebølle at the Limfjord in Denmark, the locus classicus which is eponymous for the culture, will explainits main features, along with a description of the characteristic kitchenmiddens, the “køkkenmøddinger”,because it was the investigation of kitchenmiddens that started the interest for the Danish/Northern GermanMesolithic: the big kitchenmiddens are found more easily than the small layers of other deposits which arecharacteristic for other settlements. “Denmark is one of the classic areas for prehistoric studies of shellmiddens and has a long archaeological tradition for investigations of kitchenmiddens or ’Køkkenmøddinger”’(Andersen and Johansen 1986). Kitchenmiddens are accumulations of waste (at Danish coastal sites mostlyshells) from human settlements. The first excavations on kitchenmiddens took place in 1837. In 1851 it wasshown that the investigated kitchenmiddens were not a natural accumulation of shells, although it is alsopossible that there is a natural accumulation of shells when a kitchenmidden is inundated (Richter 1986). Inthe same year, the name “køkkenmøddinger” was introduced (Andersen and Johansen 1986). This name isstill in use, synonymous with kitchenmidden, and not restricted to the Danish literature. It was found outthat the kitchenmiddens represented an earlier kind of stone age than the phase in which the well-knownmegalithic graves and polished axes emerged (which is now known as the Neolithic), and this earlier culturewas called “Ertebølle”. It is now often called Mesolithic, but because of some neolithic aspects like pottery,sedentariness and the beginning of the transition to farming, in the past the term “proto-neolithic” wassometimes preferred (Schwabedissen 1959). A newer name proposal for the time of the EBK is “NordicTerminal Mesolithic”. Hartz and Lubke (2006) differentiate so between the Late Mesolithic with typicalMesolithic tool assemblages and the EBK, whose economy is based on Mesolithic subsistence strategies,but whose material culture shows a different flint tool spectrum and the use of pottery, which connectsthem with the following fully Neolithic, culture, the TRB. Although they are a very special feature of thatculture, shell middens are not necessarily situated at Ertebølle sites. “Even within small areas, one mayfind contemporary coastal settlements with an associated Køkkenmødding and/or without” (Andersen and

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Johansen 1986). The Ertebølle site itself had been repeatedly inhabited for several hundred years before theaccumulation of the midden started(Andersen and Johansen 1986).

The shell midden at Ertebølle - one of the

Figure 3.5: The reconstructed Ertebølle settlementPhotograph by Peter Marling/Scanpix Nordfoto

largest middens in Denmark - was excavated in1893-1897 for the first time. It can be regarded asa typical Danish “køkkenmødding”. It consists ofmarine molluscs (mainly oysters), charcoal, flintdebitage, animal bone, ceramics, and stones ofvarying size. There are also fireplaces, layers ofash and flintknapping and food-processing areas(indicated by flint debitage and bones / fishbonesrespectively) in the midden (Andersen and Jo-hansen 1986). Very thick-walled pottery occursaround 3700 BC. Like other kitchenmiddens, ithas been accumulated over 700 years: the old-est 14C-date from the bottom of the midden is3,800 ± 95 BC, the youngest from the top layer is3,120 ± 90 BC, so that all dates are of a Mesolithicage (Andersen and Johansen 1986). Accumula-tion rates vary over the years, and the middensgrow also horizontally, not only vertically. TheErtebølle midden, for example, grew from north to south. The locus classicus Ertebølle will also providesome examples for the economy of that culture in section 3.3.3. A similar culture, showing the same economyand pottery, but lacking køkkenmøddinger, was discovered in Northern Germany and termed ”Ellerbekkul-tur” after the site Ellerbek, where during dredging works in the Kiel fjord many finds from former fresh waterlakes could be found in the years 1876-1903. After the insight that kitchenmiddens are not a necessary partof EBK settlements, and because there were no differences in the artefacts, if was concluded that Ellerbekand Ertebølle in fact are parts of the same culture. In Northern Germany, the Ertebølle culture is sometimesreferred to as ”Ertebølle/Ellerbek-Kultur”.

3.3.2 The environment of the Ertebølle culture

After the last ice age, the climate became rapidly warmer until it reached the high Atlantic climatic optimum(Luth, Maarleveld, and Rieck 2004). The inland ice of Scandinavia melted already in the Boreal. Duringthe Atlantic, the North American ice sheet collapsed and caused a rising of the sea level (Dellbrugge 2002).The North Sea developed in 8000 to 6000 BC, and the coast line moved in average 100m per year, so thatpeople in that time often had to move their settlements (Luth, Maarleveld, and Rieck 2004). The rising ofthe sea levels resulted since 7000 BC in the formation of the Baltic Sea, which before had no connection tosalt water and was called Ancylus Lake. The river Trave flowed in that time into the Ancylus lake (Hartzand Lubke 2006). The new sea is also called Litorina Sea after the salt water snail Littorina Littorea, andit was mainly formed during four big transgressions, the early atlantic, high atlantic, late atlantic and earlysub-boreal transgressions (Dellbrugge 2002). The formation of the Baltic Sea had a wide variety of habitatsas result, with estuarine systems being the most stable and diversified ones (Mahler 1981). The exploitationpossibilities of the different habitats will be described in section 3.3.3. At the end of the EBK, the climatedeteriorated which resulted in a scarcity of food resources, especially in winter. Oysters, which could bridgethe food resource gap in late winter, were available only in the warmer periods in Northern Denmark. Thisclimate deterioration is one possible reason for the development of farming, as will be explained in detail insection 3.3.5.

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3.3.3 The Ertebølle economy

The Terminal Mesolithic Ertebølle culture, though belonging to the Mesolithic, already shows some traits ofthe Neolithic. Besides sedentariness at places where marine resources could be exploited without the needfor nomadism and the first occurrences of pottery, the first domesticated animal, the dog, appears in thearchaeological record of the site Ertebølle (Andersen and Johansen 1986). Since the time of the Ertebølleculture, coastal settlements became important or at least for the first time visible in the archaeologicalrecord (Brinch Petersen 1993). Molluscs, fish (both marine and freshwater) and sea mammals, game like roedeer, red deer and wild boar are represented at Ertebølle sites. Bones of animals that were killed for theirfur were also found (Andersen and Johansen 1986). Big mammals were hunted with bow and arrow whichis documented by fragments of flint arrow heads that were found in bones (Hartz 1997). Carnivores androdents like marten, wildcat, otter, beaver and squirrel could also be caught in traps (Hartz 1997). Big fishwere killed with spears with fine-toothed bone points, with harpoons or nets of bast fibres while eel was alsocaught in fish traps or with wooden eel spears (Hartz 1997). Although fresh water fish provided a big partof the diet, there is evidence from some Danish sites that “even if salt-water fish contributed to diet only ina minor way, yet line-fishing from boats in a considerable depth of water must already have begun” (Clark1948). The evidence is “bones of large, mature specimens of haddock and coal fish, since both are habitableto depths from 40 to 100 metres and imply line-fishing” as the Danish coastal waters are too shallow (Clark1948).

One example for the exploitation of fish is the locus classicus, the site Ertebølle: Most of the fish bonesat the site Ertebølle are from freshwater fish with cyprinids and eel as the most prominent representatives(Enghoff 1986). Most likely, they were caught in two nearby lakes, which now have disappeared. The numberof fishbones of the different species can not be taken as a proxy for the importance of each species, becauseof the different number of bones per fish. Eel (Anguilla) has ca. 115 vertebrae, whereas cod (Gadus) onlyhas ca. 50. The preservation probability also varies for bones of different species. Bones from some kindsof fish contain more fat than others and are therefore preferred by foxes and dogs. Because of the differentstructure and composition, some bones disintegrate more easily than others (Enghoff 1986). “The rangeof marine species and their sizes indicate that they were caught in shallow water near the shore”, so it isprobable that they have been caught with fish traps (Enghoff 1986). There have been no remains of fishtraps at the Ertebølle site, but use-wear analysis on flint tools suggests the production of traps. At someother sites, though, equipment like eel prongs and fish traps were preserved.

Another example is the site “Grube-Rosenfelde LA 83” which was excavated in 2001 and 2003. In themarine coastal sediments at the former shore, remains of big animal bones in their anatomical position andrests of fish prongs were found. Additionally, large amounts of eel bones (Anguilla anguilla) were associatedwith a fireplace. This site can be interpreted as a temporarily used station for catching eel. Fresh, butotherwise useless, parts of prey could have been placed in the shallow water to attract eel (Hartz 2005). Theeel was then processed at the fireplace and the waste came into the fire and was so preserved (Hartz 2005).Eel seemed to play an important nutritional role throughout the whole EBK, as indicated by remains of eelbones, eel prongs, fish traps and weirs (Hartz 2005).

In the environment described above, three different types of adaptation, concerning the settlement pat-tern, are possible after (Mikkelsen 1978)):

1. permanent settlement at one biotope with storage to cover periods of food scarcity2. permanent base camps between different biotopes with small task groups temporarily exploiting the

biotopes3. non-sedentary, with an annual migration cycle

Although a hunter-gatherer community, the Ertebølle settlement pattern was quite stable. 13C measurementshave shown that people from coastal sites lived mainly on marine food, and that people from inland siteslived mainly on terrestrial food. “We may probably speak of large base camps occupied most of the year,with a radial exploitation pattern of the surrounding area by the help of specialized satellite extractioncamps” (Madsen 1986). There are only few hut remnants found at excavations (Andersen 1993) but larger

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accumulations of findings and the presence of some graves give hints to settlements (Kannegaard Nielsenand Brinch Petersen 1993).

Paludan-Muller (1978) investigated the ecological conditions and their influence on hunter-gatherer sub-sistence chances of different ecosystems in Northern Zealand, and his results are applicable to the whole areaof the EBK culture. Depending on their productivity, seasonality, stability and diversity, some ecosystemsare better suited for keeping a stable, sedentary population of hunter-gatherers whereas others only can beexploited by limited groups and not year-round. Estuarine systems seem to have the best conditions, becausea high productivity and diversity here results in high stability. Furthermore, the exploitation of differentresources is possible: marine and freshwater fish, molluscs and mammals, terrestrial and water plants as wellas terrestrial mammals and different kinds of birds. The seasonality in estuarine systems is small enough toallow a population of hunter-gatherers’ nutrition during all seasons. Fresh water systems are almost equallygood, but show a higher degree of seasonality, due to a lack of marine resources. Fishing at the open coastor on the sea would have been less effective than that at estuarine and freshwater systems, where the useof fish traps minimized the effort, and is therefore expected to have given a negligible contribution to theEBK nutrition. On small islands in the Baltic sea, there were peak occurrences of seal during the winter,their breeding season, so the exploitation of this resource by small task groups and in limited intervals couldhave provided the EBK society with meat, fur, fat and oil for the lamps during winter, when other resourceswere not easlily exploitable. Forest areas are expected to have been less attractive. The forests at the timeof the EBK culture had a dense canopy with few light entering the soil and therefore little undergrowth.This kind of forest is also called the ”High Atlantic climax forest” after the climatic period during that time,the High Atlantic climatic optimum. Food resources as edible plants (e.g. hazelnut or raspberry) and bigdeer were therefore mainly found at the edge of the forest, except only for mushrooms, roots and wild boar(Paludan-Muller 1978). Pollen diagrams show changes in the forest landscape during the Ertebølle culturewhich indicates a limited forestry with clearings and cultivation of grain, but with marginal economic im-portance (Schirren 1997). Clearing of the dense forests may also have had another cause than cultivation ofgrain: felling big trees and so letting more light entering the forest could have been a method to amelioratethe conditions for edible plants and deer in order to enlarge their population.

3.3.4 Ertebølle pottery and tools

The Ertebølle culture was the first North European culture that produced pottery. Normally, pottery isassociated with the introduction of agriculture, but “it is now known that pottery production precededagriculture in several instances. Instead, the basic requirement for the production of pottery is sufficientlylong periods of sedentism, spent close to appropriate clay sources and under suitable climatic conditions, toallow time for collecting raw materials and for forming, drying and firing the vessels” (Tite 2003b). Themost characteristic kind of pottery is the “Spitzboden”, the pointed base vessel or point-butted vessel. Asa second type flat bowls in boat form, called “lamps”, are found (figure 3.7). The pointed base vesselshave apparently been used for cooking food, because charred food crusts can often be found on them. Ourexperiments also show that they are well suited for cooking food (see section 4.1.3). They are in most casesbuilt up from coils which have been smoothed in a certain way so that the side of a sherd shows U-shapedlines (see figure 3.6).

The lamps are expected to have been filled with blubber or oil that was cooked out of blubber, thereforethey are also sometimes called “blubber lamps”. Experiments showed that the EBK pots are good forcooking oil out of blubber and that the lamps can be used for different purposes, depending on the wick:a small wick gives a small and very quiet, non-sooting flame, good for indoor use, whereas a thick wickproduces a very bright light that is stable under windy conditions and could for example have been used toattract fish during night-fishing or to illuminate the outdoor areas of the settlement (pers. comment Hartz2007).

A comprehensive description of the flint tool inventories of the different phases of the northern GermanEBK can be found in Hartz and Lubke (2006). In general it can be said that in the EBK, the micro-bladeflint technique of the Late Mesolithic disappears. Macro-blades produced in punch technique, transversearrowheads and trapezoidal, flat trimmed flake adzes become the most common artefacts. Transverse arrow-

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(a) Mixing clay and temper (granite chip-pings)

(b) The pointed base (c) Building up the pot in “U-technique”

Figure 3.6: Rebuilding a pointed-base vessel in the so-called U-technique

heads may not seem to be so efficient at first view, but they are in fact very useful for hunting in the forest.The arrow rotates after being shot off and so drills through the fur and skin of the deer, causing a heavilybleeding wound. It is not possible to kill a deer with that arrow with a single shot, but it is easy to followit after the blood it loses. Borers and burins were made out of flint stone flakes, but also ground stone toolssuch as round-pecked axes can be found.

3.3.5 Transition to farming: From Mesolithic to Neolithic or from Ertebølle toFunnel Beaker culture

The introduction of agriculture and animal husbandry marks the transition from the Mesolithic, the middlestone age, to the Neolithic, the younger stone age. This process is called neolithisation and is the mostextensive change in human life conditions that happened in Europe until today. In the course of fewgenerations, not only the way of food production changed, but also the type of society, beliefs and technology(Andersen 1989). For some regions, it is therefore also called “neolithic revolution”. In Southern Scandinavia,where the change happened gradually, this term is maybe not appropriate. In 4700 BC, the first potterycame to southern Scandinavia, but a real farming culture did not occur before 4000 BC (Andersen 1989). At3900 BC, the culture change was completed and the Funnel Beaker Culture (TRB) established (Andersen1989). In Northern Germany, the oldest pottery was produced around 4750 BC, if we exclude the potterywith uncertain ages because of a possible reservoir effect (Hartz and Lubke 2006). The introduction of potteryin Northern Germany and Denmark can therefore be characterized as being happened contemporarily. Thenew way of producing food necessitated also new technologies, so that there was a big change in the toolinventory (Andersen 1989). A consistent chronology of the whole Neolithic in Europe is hard to achievebecause of the cultural diversity during that time. Some parts of Europe were inhabited by hunter-gathererswhile elsewhere, farming societies had lasted for a course of many generations. Anyway, the chronologyneeds a stable framework that is independent of cultural groups. Cultural groups that are found or definedin the future can so fit into that framework (Fischer 1976).

The transition was not only economical, but also social and religious: from the “egalitarian” hunter andgatherer society to the ranked farmer society, with a completely different perspective towards its territory.Storage of harvested goods caused the division of production and consumption and necessitated a controllingfactor which finally ended with a hierarchical society. Also the attitude towards the land changed: agriculturerequires fields which belong to the people who work on these fields, so the protection of the territory suddenlywas a very important task (Mahler 1981). As the transition to farming took place at the end of the EBKand as pottery is one of the aspects of neolithic cultures, the dating of EBK pottery will provide informationabout the process of neolithisation in Northern Germany. Therefore, I will now describe possible theoriesabout the transition from Mesolithic to Neolithic in some detail, because the results of the datings and

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(a) Pointed-base vessels (unfired) (b) Pointed-base vessels and lamp(fired)

Figure 3.7: Ertebølle pottery (copies). Photographs by Aikaterini Glykou.

isotope measurements have to be interpreted in terms of culture change and contacts to other cultures.

Why is it hard to explain this transition?

Normally, the transition from a hunter-gatherer to an agricultural society is regarded as natural because it isa form of progress. Farmers are regarded to have a higher security regarding the availability of food resources.An agricultural, stratified society with division of labour is also able to make bigger cultural achievements.In the area north of the lower Elbe, the EBK area, the question why people gave up hunting and gatheringto start farming is hard to answer, because the life of a farmer is harsher than that of a hunter-gathererin that region. The neolithisation, which proceeded from the Eastern Mediterranean throughout Europewith a speed of approximately 1 km annually, reached central and northwestern Europe around 6000 BC(Andersen 1989) and stopped from 5000 BC on at the lower Elbe for 1000 years (Fischer 1974), because theintroduction of agriculture was not necessary north of that region: The productive coastal zones providedenough food for the whole population so that the Mesolithic economy with its low labour demands couldexist there for a long time. This is called the “Garden of Eden” argument (Madsen 1986). The work effortof a hunter-gatherer community for example consisted of only 2-3 days per week, while farmers had to workmuch longer to achieve the same amount of food (Fischer 1974). The higher mobility makes it furthermorepossible for hunter-gatherer communities to move to richer regions in case of food scarcity, while farmers arebound to their settlements with their fields and crop. There is even archaeological evidence for the flexibilityof the EBK community: The number of Ertebølle sites increased strongly when the sea level rose and marineresources came into the Danish baltic sea which points to a flexible, fast reaction (Rowley-Conwy 1985). Thehunter-gatherer subsistence strategies provided sufficient nutrition as can be seen on skeletons from EBKgraves. Furthermore, the absence of caries and chronic diseases, apart from gout with aged individuals, isa sign for the balanced nourishment of the Mesolithic population (Kannegaard Nielsen and Brinch Petersen1993). In the past, the introduction of agriculture was, as most big changes in society and economy, explainedby immigration of groups that already used all these new techniques. But the archaeological record givesanother result, for example in the area examined here, the south-eastern part of Schleswig-Holstein. Here,the mixed Mesolithic and neolithic material of some sites indicates a site continuity. The preferred settlingregions of the Mesolithic and the Early Neolithic correspond for example in the range of the rivers Trave

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and Alster. Theses areas probably kept their economic importance as fishing and hunting stations until thebeginning of the bronze age (Schirren 1997).

Different phases in the transition

The adaptation of agriculture and the development to a neolithic society takes place in a process which can bedivided into different phases. There is one advantage when examining this process in Southern Scandinavia:

The transition to farming in the European part of the boreal zone was a far more gradual processthan elsewhere in Europe. This makes it possible for archaeologists to trace the transition tofarming at a finer level of resolution and to isolate discrete phases in the decelerated evolution ofsettled farming communities (Zwelebil and Rowley-Conwy 1984).

One can divide the process of adaptation of farming into three phases, from a phase of availability tosubstitution and finally consolidation.

How these phases are reflected in the archaeological material from Schleswig-Holstein

The Ertebølle culture existed at the same time as the Central European Early Neolithic sedentary Linearpottery and Post-Linear pottery cultures (Hartz and Lubke 2006). Around 3400 BC, at a former bay onthe Baltic sea coast of Schleswig Holstein, the “Dahmer Bucht”, a strong influence from southern culturesis visible. Parallels to the Neolithic “Michelsberg culture” show the close cultural contacts which now linkNorthern Germany closer with the Central European development (Meurers-Balke 1983). The eastern partsof Holstein seem to have been a center of commerce between Eastern Denmark and the neolithic settlementareas at the Elbe, as for example Danubian axes on the sites Grube-Rosenhof and Neustadt show (Hartz2005). Hartz and Lubke (2006), though, warn that not every innovation is a sign of contact to neolithicculture groups: “Certain elements in the artefactual record, such as pottery or T-shaped antler axes, whichhave always been interpreted as Neolithic influences, could originally have come from other Mesolithic groupsin northwestern Europe or the Baltic”. But one artefact group clearly is an indicator of contacts to Neolithiccultures: Findings of shoe last axes show contacts to central Europe or in fact even to the Balkans; inDenmark (Fischer 1993) as well as in Schleswig-Holstein (Schwabedissen 1979). So, in the case of EBK toTRB, the availability named by Rowley-Conwy (1984) was provided through contacts to the Michelsbergculture and further south (Fischer 1993).

Nevertheless, the EBK phase of Rosenhof at the Dahmer Bucht can not be regarded as fully Neolithic.Some of the first proofs for a beginning neolithisation have been argued against: There are only two bonefragments of domestic cattle, which does not indicate that stock-keeping was an important food source,especially not because the cattle could have come (donated or traded) from the Michelsberg culture. Tracesof cereal pollen could have been spuriously identified, while a potsherd with a grain impression is alsoprobably a Michelsberg import, like other imported pots from Michelsberg and Baalberge (Zwelebil andRowley-Conwy 1984). The uncalibrated 14C age for the finds of domestic cattle is 5960 ± 65 BP (Heinrich1993).

New excavations at Rosenhof in 2001 and 2002 showed a closed find inventory from the time between4800 and 4500 BC (calibrated age) with a lot of Ertebølle tools but no signs of agriculture or stock-keeping(Hartz and Schmolcke 2006).

“The availability phase ends with the adoption of at least some elements of farming by the foragers, orwith the settlement of farmers in the territory hereto exploited by hunter-gatherers” (Zwelebil and Rowley-Conwy 1984). Thus, the availability phase comprises the early and classic Ertebølle and lasted for more than1000 years (Zwelebil and Rowley-Conwy 1984). Pottery and more or less strongly developed sedentarinessfor example have been adopted very early.

In former times it was believed that the EBK and the Funnel Beaker culture (TRB) “ran parallel for aconsiderable amount of time” (Madsen 1986). But since the 1970s, when 14C dates from EBK and TRBbecame available, it was known that they were not contemporaneous but followed each other, which is alsovisible at some sites with both EBK and TRB finds (Andersen 1989). “Hunting, fishing and gathering was

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the main form of subsistence on all northern German and southern Scandinavian Ertebølle sites” (Hartz andLubke 2006). Even in the “full Neolithic”, in the Funnel Beaker culture, hunting, fishing and gathering stillplayed an important role. The strong links and a possible continuity from Ertebølle to Funnel Beaker canfor example be seen on neighbouring sites on the former “Dahmer Bucht”: Siggeneben Sud and Rosenhof,as well as Wangels, 15 km west of Rosenhof.

On the former coastal site Siggeneben Sud, for example, hints for farming and cattle have been found,but there were also rests of hunting and fishing equipment (eel prongs, spears). The findings propose that“Mesolithic” and “Neolithic” economy were equally important on that site. Siggeneben Sud has been radio-carbon dated to 3200-3000 BC (Meurers-Balke 1983).

On the neighbouring site Rosenhof, whose main layer consists of Ertebølle remains, the economic situationwas approximately the same, but hunting, gathering and fishing played a more important role while therewere only small beginnings of agriculture and cattle. When comparing these two sites, one finds a continuityfrom Ertebølle to Funnel Beaker. On the bottom layer of Rosenhof, there are pointed base vessels andlamps. Its younger pottery shows a strong influence of the Michelsberg culture and leads to the FunnelBeaker culture. In the following phase, which is situated at Siggeneben Sud, there is a broad spectrumof funnel beakers and flasks. The strong links to the Ertebølle culture are proved by the occurrence oflamps in the early Funnel Beaker culture. Although these differences in the pottery define the two differentcultures, the inventory of stone, wooden and bone tools from the two sites is morphological and quantitativelycomparable. There are only some tendencies that would show a technological change, like the changes inpottery and in stone tool technology (blade technology decreases in importance, the first polished axes areproduced). As a conclusion, there must have been comparable activities during Ertebølle and Funnel Beaker.

Wangels has been excavated from 1996 until 1999 and contains elements both from the late EBK aswell as from the early TRB. Pointed base vessels and lamps have been food-crust dated and belong tothe time before 4100 BC. A completely different type of ceramics was dated to 4100-3800 BC: decoratedfunnel beakers, flasks, beakers with ears, thin-walled bowls and pots with round bottom which represent therepertoire of the earliest TRB. There are also changes in the stone tool industry: polished axes, made fromimported stone, occur for the first time, as well as core axes with specialised cutting edges. The rest of thestone tool spectrum remains unchanged and continues EBK traditions. In contrast to Rosenhof, there arehints for a developed crop-keeping in Wangels, as the archaeo-zoologist Dirk Heinrich has found out: Twothirds of all mammal bones are from domesticated animals, with cattle as the biggest group (two thirds ofall domesticated animal bones). Sheep/goat1 bones already occur 4200 BC, before the culture change fromEBK to TRB, whereas cow bones date only back to 4100 BC, the time of the culture change. There arealso signs for agriculture: pollen of emmer wheat, one charred emmer grain in a potsherd, imprints of grainspikes on a sherd and fragments of mill stones (Hartz and Schmolcke 2006).

The substitution phase is therefore visible already in the late EBK layers, as in Wangels, where forexample sheep/goat is found. The consolidation phase is the beginning of a new fully Neolithic culture, theTRB, in Denmark for example in 3900 BC (Andersen 1989). It developed on the basis of a EBK that alreadybegan using some Neolithic techniques.

Different models

For the explanation of the Mesolithic-Neolithic transition, different scientists focused on different aspects.This resulted in a number of different models.

Climate change caused a shortage in food resources The transition from atlantic to subborealclimate brought about some major changes: summer temperatures which were 2◦C lower as well as lowersalinity, temperature and nutrient content of the sea water. The adoption of farming has been explained atleast for the Ertebølle kitchenmidden sites in western Denmark where a lower salinity once led to a lowercontent of oysters in the fjords. The oysters were bridging a food gap in late winter/spring, and when they

1Sheep and goat bones are hardly distinguishable. Therefore, in most cases they are stated as “sheep/goat” instead ofdeciding for one denotation.

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disappeared, something else was needed to bridge that gap. Because farming was done by communities inthe south and because there were contacts between these different groups, it was likely that farming wasadopted to have something to eat in the times when there were no other matching resources available. Deer,for example, has a very low fat content at the end of the winter (Rowley-Conwy 1984). The gap after thedecline of oyster could have been filled with the cultivation of cereals. But then, there was a competitionfor labour during autumn, which is the most labour-intensive season for both hunter-gatherer and farmingcommunities. If some of the hunter-gatherer activities “were displaced by farming activities, it would belogical to expand the farming sector still further to compensate” (Zwelebil and Rowley-Conwy 1984). Butfor the inland and for the coastal sites without kitchenmiddens, that is, for sites where oysters were not animportant resource, there must be another explanation.

Catastrophe theory While in former times “abrupt” changes in the prehistorical societies have beenexplained with immigration of other people, many researchers now prefer to use models of “catastrophetheory”, i.e. that abrupt breaks in the archaeological record can be caused by slow, ordinary, everydaychanges in local society. The archaeological record does not represent all the possible choices available in asociety, but only the chosen ones, so that the knowledge for agriculture can have been available for a longtime without being used. “The claim is that hunter-gatherers live a secure life, and that stable equilibriumis the hallmark of their cultural system”, but is has to be considered that “many systems cannot be stableunless they change”, and that a constant change is possible without being reflected in the archaeologicalrecord. Only when all the small changes sum up and cross a threshold, one sees an “abrupt change” (Madsen1986). Because of this abrupt change without visible cause, this theory is called “catastrophe theory”. Smallchanges in the EBK daily life could for example be

• growing knowledge of agriculture due to contacts with farming communities

• growing sedentariness at places with high productivity such as estuarine systems

• storage of hunted and/or gathered food for times with lower productivity , which both is a result ofand a cause for a higher degree of sedentariness

• changing the natural environment for increasing its productivity, for example clearing the dense forestto make better conditions for fruit-bearing trees and wild game

Storage of food and systematic changes of the natural environment already lead to a different social model:The production and consumption of food are separated and division of labour has to be planned. Therefore acontrolling entity is needed (Mahler 1981). These small changes which are hardly visible in the archaeologicalrecord result in a sedentary society with a broad knowledge on agricultural and storage techniques which isalready used to influencing the environment according to its demands. In this society, it is only a small steptowards the adaptation of agriculture, which could be caused even by minor changes in the environment atthe end of the Atlantic period: A population whose subsistence is partly based on storage can be destabilisedmore easily than a fully Mesolithic society. Agriculture could therefore be used to substitute food shortages(Mahler 1981).

Progress Model and Evolutionary Model The progress models say that farming is progress and there-fore automatically adopted when the environmental conditions are appropriate. To the contrary, farmingtechniques were available for 1000 years but still not adopted in Southern Scandinavia, although the popu-lation lived on the right soils – light, but fertile – and in the right climate for farming. Therefore, progressmodels are of no use for the EBK situation (Rowley-Conwy 1985). Close to the progress models is theevolutionary model that assumes processes like cultural evolution, for example a growing social structuring,to be the cause for changes in food production techniques.

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Population Growth Population growth or population press models say that the growing population ledto a more extended exploitation of the Mesolithic resources, increasing the number of working hours neededfor one unit of food. Finally, more working hours per food unit are needed in a Mesolithic than in a Neolithiceconomy. At this point, assuming the contact to Neolithic groups, agriculture is introduced (Fischer 1974).The longterm population growth models assume that there is always a population growth and that this wasthe reason for introducing agriculture. However, the population is fluctuating regionally much stronger thanglobally so that there is no constant population growth in a certain area. Therefore is it not an explanationfor the adoption of agriculture (Rowley-Conwy 1985). It can often be observed that population growth takesplace after the introduction of agriculture. A growing population is in fact one of the characteristics of theNeolithic. This is also the case in the region examined here. First in the advanced Early Neolithic of theFunnel Beaker culture there are more findings / bigger concentration of findings in most regions. Assumingpopulation growth to be a reason for the adaptation of farming would mean mixing cause and consequence.

In opposition to the longterm population growth model, many people assume population size “to bea factor that is fully controlled by homeostatic mechanisms in the system” (Madsen 1986). In agreementwith the New Archaeology since Binford, “[s]ome unexpected change in the equilibrium level of the systemhas to take place” (Madsen 1986) to cause a population pressure. Therefore, the arguments stating thatagriculture was adopted because of a growth in population do not refer to the direct cause. Another, somehowmore “marxist” model also stresses the importance of population growth, but it takes the reasons for thatpopulation growth into account and acts on the assumption that

an imbalance between population level and food resources created a growing sedentism basedon seasonal resources (fish) that could be stored. The sedentism, then, resulted in a growingpopulation, whose demands for food led to a perfection of the catching and storing technology,so that more fish could be “harvested”. Subsequently, this development led to a depletion (over-fishing) of resources. The only possible answer to this was to adopt agriculture ((Madsen 1986),summarizing (Mahler, Paludan-Muller, and Hansen 1983)).

As it is now known that there was a decline in temperature and therefore a change in the environment atthe end of the EBK, over-fishing is now not longer needed as an explanation for the beginning scarcity ofresources.

The fertile gift Another model that does not need population pressure as explanation is that of KristinaJennbert who proposes to regard grains and cattle as prestige goods that were in the beginning not used fornutrition, but mainly as signs of prestige after contacts with agricultural societies. She bases her argumenton sites in Scania where there is continuity between Ertebølle and Early Funnel Beaker, but no indication fora decline in food resources (Jennbert 1985). Some single findings point to contacts between fully Neolithicgroups and the Late Mesolithic. So the exchange of prestige goods as “gifts” between different cultures isconceivable.

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Chapter 4

The samples from Schlamersdorf andKayhude

Here, I will explain the different kinds of samples I have taken as well as the way of sampling and pretreatment.Measurements and results will also be given.

4.1 Selection and pretreatment of samples

To ascertain a hardwater effect, both modern and old samples were chosen. Firstly, water samples fromthe rivers next to the sites were taken, because the radiocarbon age of them can give a hint on a possiblehardwater effect. Secondly, recent fish and mollusc was chosen, in order to show that the hardwater effectis passed on from the water through water plants and finally fish. For finding out if the age of the fish alsoaffects the age of a food crust, food crusts both from fresh terrestrial as well as freshwater material wereproduced and pretreated in the same way as the old food crusts. As one could doubt that the carbonatecontent of the rivers as it is measured now is the same as in the Mesolithic/Neolithic, also old samples hadto be taken. First of all of course food crusts were dated because samples of this type were taken beforeto date the first occurrence of pottery in Schleswig-Holstein and showed surprisingly high ages. In order todiscover a hardwater effect in the archaeological material, associated samples of terrestrial origin on the onehand and freshwater origin on the other hand had to be dated. Therefore fishbone, bone, charcoal and woodsamples from the same layers and not too far away from each other were chosen.

4.1.1 Water samples

On each site, three water samples have been taken. One directly next to the site, on upriver and onedownriver of the site. Dissolved inorganic carbon was extracted from the samples that were taken directlynext to the sites (called “Trave 1.1” and “Alster 1.1”) and converted into graphite samples. The other twosamples from each river were kept for the case that “Trave 1.1” and “Alster 1.1” got lost during preparationor measurement. They can now be used for further examinations, for example chemical analyses or theextraction of DOC which might be necessary to explain some of the dating results (see section 4.2.1 and4.2.3).

On the same day on which the water samples were prepared, a background sample was also preparedto get an idea of the background contamination that enters the samples in the CO2-extraction process andfollowing graphitisation. For the preparation of a water background sample, a half-liter bottle is filled withdemineralized water and 30 mg Iceland spar, in Danish “dobbeltspat”. It is a variety of crystallized calciumcarbonate, CaCO3. 30 mg Iceland spar correspond to 3.7 mgC. 4 ml 85%H3PO4 (phosphoric acid) are addedto dissolve the carbonate over night at 80◦C. After cooling down for one day, the background sample wasprocessed in the same way as the other water samples.

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In our laboratory, in most cases only DIC is extracted from the water (see section 1.2.3). Water samplesare taken with half-liter amber glass bottles which were rinsed with acid and deionized water and dried. Whenthe water samples are taken from the river, it is paid attention to closing the cap under water or shortly afterfilling the bottle so that no atmospheric air can enter the sample. Three to four drops Mercury(II) chloridesolution, also known as mercuric chloride, HgCl2, are added to prevent algae growth. The concentrationof this solution is 3.5 g HgCl2 / 50 ml water. Mercuric chloride is used because it is one of the forms ofmercury that is most soluble in water and because of its high toxicity that prevents all forms of biologicactivity in the water sample. This preservation is necessary if the sample can not be kept cool all the timebetween collection and measurement and if the measurement takes place later that a few days after collection(Clark and Fritz 1997). In the laboratory, the samples are stored in a fridge until the DIC is extracted. Fortransferring the sample to the DIC extraction system (in the following called water system), the samples ispumped from the bottle to an evacuated flask that is connected to the extraction system. If one would pourthe sample into the flask instead of pumping it through a rubber tube, it would have too much contact withatmospheric air. 223.6 g water were taken from the background sample, 216.2 from Trave 1.1 and 216.5 fromAlster 1.1 for DIC extraction. In figure 4.1, the DIC extraction from water samples at the water system isshown. The water system is filled with about 600 torr nitrogen gas (N2(g)). 4 ml 85%H3PO4 (phosphoricacid) are filled into the flask with the sample (figure 4.1a). The N2(g) is pumped through the sample ina closed circuit, “bubbling out” the CO2 that formed from the DIC when phosphoric acid was added tothe sample (figure 4.1b). The CO2 is frozen at two freeze traps (figure 4.1c and d). After 15 minutes, thenitrogen is pumped away and the CO2 is defrozen and its pressure is measured in a calibrated volume. Fortransfer to the graphitisation system, the CO2 is frozen into evacuated glass tubes which are flame-sealedafter the sample is filled in. From the 216.2 mg Trave water, 3.5 mgC could be extracted. That correspondsto a carbon yield of 1.6%. The Alster water sample with 216.5 mg water yielded 7.18 mgC. That correspondsto a carbon yield of 3.3%. The amount of DIC extracted from the Alster water is thus twice the amountextracted from the Trave water. This result is strange because the Trave water had a hardness of about13◦dH, the Alster water about 10.5◦dH, as was explained in section 3.2.1. As the water hardness is theconcentration of the alkaline earth metal ions, predominantly Ca and Mg, it is an indicator for the amountof dissolved carbonate in the river water. The carbon yields from these two samples show that other sourcesof DIC than carbonate mineral dissolution must be taken into account for the Alster.

Some graphitisation parameters are changed when water samples are graphitised. The first is that thewater trap the samples have to pass at the graphitisation system has a temperature of -110◦C instead of thenormally used -80◦C. The reason for this is the higher water vapour content of the samples that necessitatesa more efficient removal of water. The laboratory experience shows that the graphitisation rate of watersamples is lower than that of other types of samples. A possible reason is that the surface of the catalystis covered with contamination from the water sample so that the reaction surface for CO2 is reduced. Forenhancing the graphitisation conditions for water samples, the catalyst amount is enlarged from 0.8 to 1.1 mgcobalt. Furthermore, a small stripe of silver foil is placed in the reaction tube to absorb contaminants likesulphur compounds.

4.1.2 Recent fish and molluscs

Richter (1986) found out in experiments on recent fishbone (vertebrae) that collagen degrades when heated:Thermal denaturation of the bone at 60◦ C caused melting of the collagen in local areas both at the endsand along the fibril. Melting progresses with higher temperature and a decreasing fraction of the fibrils isnative collagen so that at 80◦ C only small fragments of collagen fibrils with melted (swollen) ends can beseen. Vertebrae heated to 100◦ C showed no signs of any fibers which could be identified as collagen, neitherwhen it was heated with nor without tissue attached. She uses the degradation of the collagen as a hint iffishbones have been heated (and so form an anthropogenic deposit) or not. Exceptions are of course biggerfish that were boned before usage.

When the bones are prepared in our laboratory, they are sometimes ultrafiltered, because contaminantsare likely to consist of smaller molecules while the original bone material consists of bigger molecules. Becauseof the above-mentioned degradation of collagen, it was suspected that cooked bones give a smaller yield after

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(a) Flask with sample (b) Bubbling N2(g) through the sample

(c) Freeze-trapping of CO2 (d) The frozen CO2

Figure 4.1: The preparation of water samples (DIC extraction)

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ultrafiltration than uncooked bones, because the degraded collagen molecules could be too small to stay inthe filter. To test this, cooked as well as uncooked fresh fishbones from the river Trave have been preparedand the preparation yields have been compared. The fish was cooked in water in a pointed base vessel,standing on three stones and heated by a small fire which mainly consisted of glowing charcoal. After only15 Minutes, at a water temperature of 77◦C, the fish was already done and taken out of the pot. It can beexpected that the temperature in the bones did not rise above 70◦C and maybe even stayed under 60◦C,so that a degradation of the collagen, as Richter (1986) experienced, possibly did not take place in ourcase. This fits well to the result that there is no significant difference in the preparation yields (extracted“collagen” weight compared to sample weight), and the yield of the cooked bones is even a little bit bigger.Therefore, ultrafiltration can also be applied to fishbones that are likely to have been heated, because it isunlikely that a stone age fish meal was heated much longer than to that point where the fish was done andready to be consumed. The bones were chosen to be dated, and not the flesh, because the results should becomparative to the archaeological material, which only provides bones of the fish.

The recent fish bones from the river Trave were prepared after the following method: They were putinto a glass with demineralised water and cleaned (i.e. the remaining tissue was removed) with tweezersand scalpel. The cooked fish bone was clean and white after this procedure, but there was a lot of tissueremaining on the uncooked fishbones. Therefore, they were additionally cleaned with demineralised waterin an ultrasonic bath, first for 10 minutes, then for 30 and finally for 60 minutes. Because there was stilltissue adhering to the bones, another cleaning step with ultrasound and acetone for one hour was performedbefore the samples were dried overnight at 56◦C. The recent fish bones from the river Alster only neededthe following cleaning procedure: Two times ultrasonic bath (with demineralised water) and cleaning withtweezers and scalpel in between before they were dried like the Trave fish bones. The chemical pretreatmentof the bones with ultrafiltration is described in section 4.1.5. The fresh fish bones were pretreated in the sameway as archaeological bones and fish bones to provide comparable results. Additionally, one snail-shell fromthe Alster was dated. It was cleaned in demineralized water in the ultrasonic bath for about two minutes.Thereafter it was dried and weighed. The outer parts of the shell were etched with 40 µL 1M HCl per 10 mgshell in demineralized water. A treatment with 7 to 8 drops 0.25M KMnO4 in 25 mL demineralized waterfollowed. This was done for 16 to 20 hours at 80◦C. Figure 4.2 comprises the recent fish and shell samplesfrom both rivers.

4.1.3 Recent food crusts

Experiments with the formation of food crusts were conducted to get answers to problems like formationtime and probability as well as alteration of chemical composition and isotopic values during the process ofcooking and food crust formation. Experiments like these never reflect the complete prehistorical situationand are not suited as a definite proof for a certain theory of prehistoric man’s behaviour, but at least theycan show possibilities - and impossibilities. As Charlton (1981) remarks,

In considering the applicability of data from experimental archaeology it is necessary to keepin mind the probabilistic nature of inductive argument by analogy and the importance of therelevance of the claimed similarities and differences. Among those who have examined this aspectof experimental archaeology there is general agreement that such studies serve to strengthen thebases for inference via analogy by eliminating irrelevant alternatives for a given phenomenon.

In the experiment, two types of food crust were produced: Recent fish (roach) from the Trave and recentwild boar meat were cooked in Trave water until the water was boiled away and the food burnt and formeda crust on the pot. To copy the prehistorical situation best possible, copies of pointed base vessels wereformed by Harm Paulsen, experimental archaeologist in Schleswig. The pots were tempered with crushedred granite (see picture 3.6a on page 65). It is relatively easy to crush the granite stones when they havepreviously been heated, as is the case for pot boilers or stones that formed a fire place. The finished pots(figure 4.3) were then dried for 15 days at room temperature.

The firing also was done copying the prehistorical conditions. First, a spot of soil was cleaned of grassand levelled. This place was dried and warmed by a fire, because firing the pots directly on the cool soil could

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(a) Fresh fishbone (Trave), SID 12060 (b) Fresh cooked fishbone (Trave), SID 12097

(c) Fresh fishbone (Alster) (d) Snail-shell (Alster)

Figure 4.2: Photographs of the modern fish and shell samples.

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cause them to break, due to the temperature differences between soil and fire (pers. comm. H. Paulsen 2007).When this first fire was almost completely burnt down, it was pulled apart (figure 4.4a) and the pots wereplaced in the middle, with the top facing down (figure 4.4b). Now, the ring of embers surrounding the potswas fed with more firewood and slowly brought closer to the pots, so they heated up slowly (figure 4.4c). Theslow heating process is necessary because the thick walls crack easily when there are too high temperaturedifferences between to places on the pot. Especially the thick pointed bases are very fragile. We could alsosee the that two of the pointed bases cracked away from the pots, one pot therefore having a hole and beinguseless, another one only missing the pointed base (and so showing the silhouette of a funnel beaker).

When the fire finally covered the pots, ca. 30 minutes after the pots

Figure 4.3: Finishing a pointed-base vessel

had been placed onto the firing site, it was heated up and a more woodwas put on the fire little by little, so that a big fire was burning for ca.20 minutes (figure 4.4d). After that, the fire was left to burn down toashes (figure 4.4e), which took two hours, and the pots were carefullyrolled away from the firing site (figure 4.4f).

These conditions are comparable to the assumed prehistorical openfiring, described by Tite (2003b): The bonfire reaches the maximumtemperature in 20-30 minutes, while the maximum temperature is main-tained only for a few minutes (in our case: when all the wood was puton the fire, the fire had its maximum temperature, before it was left forburning down). After 20 minutes of cooling, the pots still had a tem-perature of more than 90◦C. As the sand on the firing site was colouredred and the pots clinked when one knocked at them, a firing temper-ature of 600-700◦C could be assumed (because of a broken device, wewere not able to measure the firing temperature directly). This is again

comparable to the archaeological experiences: in an open firing, maximum temperatures reach from 500 to900◦C, in most cases between 600 and 800◦C. The firing atmosphere in an open fire can change rapidlyfrom reducing to oxidising, and fully oxidising conditions are reached very seldom, because the pottery is inintimate contact with smoky and sooty fuel (Tite 2003b). The latter description also fits to our pots: Theyhave an irregular colour, partly reddish and partly dark, so the firing was a mixture of oxidized firing andfiring in oxido-reducing atmosphere (figure 4.4f).

One pot was filled approximately half full with fish (without head and fins, but still with bones) and alittle water so that the fish pieces were covered. The water was taken from the Trave and still containedsome plant pieces, both terrestrial and water plants (as the river had high tide and was flooding surroundingfields), which is likely to reflect the prehistorical situation (some plant material might have been used asspice, for example). A second pot with wild boar meat was prepared in the same way. It could be seen thatafter a short while, the “meals” were done, with most of the water still being in the pots and not crusts onthe inner surface of the pots. Therefore, the small hearth fires were enlarged and kept burning for a longtime in order to make food crusts. It took almost two hours until the water of the fish soup was boiledaway, and from the heating of the wild boar meat until a food crust was formed, it took almost three hours.Therefore, we can say that the formation of a food crust is a very unusual event which requires a lot of timeand energy, assuming the use of some water in the preparation of stone age food. Another observation isthe very unpleasant smell of the crusts, which makes further use of the pots after the formation of a crustimprobable, taking into account the refined sense of taste of a population that had no access to strong spicesor artificial flavours, but depended on the sense of taste to chose between edible and poisonous plants. Thelittle work that is required to build a pointed base vessel is another argument for the discarding of pots assoon as a crust was on it. These observations now necessitate an explanation for the large number of foodcrusts that can be found on EBK sites.

The fish food crust was coloured light brown to black. Some fishbones were visible on the surface, whileother fishbones were charred and only visible as imprints. The boar food crust was a homogenous viscousblack mass. After cooling down, it divided into two crusts: one part firmly adhering to the pot under anotherbrittle and easily removable crust with air bubbles. The food crusts were pretreated in the same way as old

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(a) Preparing the firing site (b) Placing the pots on the prepared ground

(c) Bringing the fire closer to the pots (d) Firing

(e) The fire burns down (f) The pots after firing

Figure 4.4: Firing of the pointed-base vessels. Photographs by Aikaterini Glykou

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(a) Fish soup gets heated (b) The water of the fish soup is com-pletely boiled away

(c) Fish food crust

(d) Meat soup gets heated (e) The meat soup is boiling (f) Meat food crust

Figure 4.5: Food crust production from fish (roach, a-c) and meat (wild boar, d-f).

ones (see the following section, 4.1.4), to give comparable results.Later, the team of archaeologists from Schleswig was able to get blubber from a beached whale (porpoise)

on the west coast of Schleswig-Holstein. They cooked blubber in a pointed-base vessel and also scorchedsome of it in the pot. This makes it now possible to examine the difference between original material andcrust also for a marine sample. The oil that was cooked out of the blubber was then used for filling a copyof the typical EBK lamp (pers. comment Sonke Hartz 2007). See sectionrefsec: ertebolle-pottery-and-toolsfor a description of the lamp.

4.1.4 Old food crusts

At Schlamersdorf, two different pottery wares could be found. One of them is thick-walled, tempered withreddish granite chippings and made in U-technique. The other is thin-walled, contains fine temper particlesand is made in U-technique and “Schrgaufbau”. Most of the food crusts were pretreated according to thelaboratory’s standard pretreatment procedure for plant rests, food crusts and charcoal: The food crusts wereexamined under the microscope and visible contamination such as rootlets were removed. Then the crustswere scraped off the sherd with great care, so that no clay material was abraded. When available, both theinner and outer crust of a sherd were used. Without a hardwater effect it is expected that the outer crusthas the same or a higher age than the inner crust: The inner crust is expected to have formed from charredfood whereas the outer crust can consist of food that boiled over or of soot from the hearth fire. Soot fromthe hearth fire can have a higher age than the charred food remains if old wood was used (“old wood effect”).

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In two cases, plant remains were found inside the sherds, and one of these sherds also had an outer crust sothat it will be possible to compare dates of three fractions from the same sherd (see table 4.1). It is hardto say if the plant remains entered the clay during the production of the pot or if they stem from rootletsthat grew through the sherds during their deposition in the soil. As the clay was tempered with granitechippings, organic temper can be excluded as a source of plant remains. If the plant remains were originallymixed into the clay, they are expected to have the same 14C age as a food crust from terrestrial material.Otherwise, a much younger age is expected.

Table 4.1: Pottery sherd samples from Kayhude and Schlamersdorf: sample type, NaOH concentrationapplied in the pretreatment procedure, and pretreatment yield.

SID Find No. Sample Sample size NaOH Sample size Yield Cathodematerial (mg) before conc. (mg) after (mg/ number

pretreatment pretreatment mg)

12047 KAY8-432,01 Food crust 68.9 1M 50 0.726 19899Humic 68.9 0.4 0.006 19900

12048 KAY8-168,01 Food crust 40.2 1M 27.7 0.689 19901Humic 40.2 2.2 0.055 19902

12053 N-629 Food crust 42.8 1M 22.3 0.521 19904Humic 42.8 4.0 0.093 19905

12054 N-629.1 Food crust 32.8 1M 18.7 0.570 1990612055 SL1 Modern food crust 83.2 1M 0 0 . . .

Humic 83.2 35.6 0.428 1992512056 SL2 Modern food crust 40.1 1M 0 0 . . .

Humic 40.1 14.8 0.369 . . .12057 SL3 Modern food crust 61.6 1M 40.4 0.656 . . .12058 SL4 Modern food crust 65.2 1M 15.8 0.242 19926

Humic 65.2 10.8 0.166 1992712345 KAY8-412,01 Food crust 43.6 1M 31.7 0.727 1992812347 SLA5-1713 Food crust 29.3 1M 20.4 0.696 19979

Outer crust 14.2 0.5M 9.8 0.690 19974Plant remains 0.6 0.2M 0.3 0.500 20502

12348 SLA5-2707 Food crust 17.9 0.5M 13.3 0.743 1998012349 SLA5-2742 Food crust 26.9 1M 18.8 0.699 19981

Plant remains 3.6 0.2M 2.0 0.555 19977

First, the food crusts were treated with HCl at 80◦C for 1 hour to remove any carbonate. After rinsingwith demineralized water to remove the dissolved material, humic substances were dissolved in NaOH andthereafter washed away with demineralized water. The samples were then acidified with 1M HCl over nightto remove any CO2 absorbed during the NaOH treatment (Olsson 1976a). The usual NaOH concentrationfor food crust pretreatment is 1M, but for very small samples, less concentrated solutions were used. Whenthe NaOH solution was coloured very dark after the first NaOH step, the solution was not poured away butsafed in a glass beaker and acidified with HCl and heated so that the humic substances precipitated. Theprecipitated humic substances were rinsed with demineralized water and dried. As described in section 2.1,humic acid precipitates at pH < 2 whereas fulvic acid is soluble at all pH values. The precipitated substancefrom the sample is therefore expected to be a mixture of acids present in the food crust, for example fattyacids, and humic acids. The fulvic acids which is present at all pH values should have been removed alreadyin the first rinsing procedure. The NaOH step was repeated until the solution was clear. The samplesof modern food crust from wild boar meat dissolved completely under NaOH treatment. Therefore, only

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the precipitated “humic substances” could be dated. In this case, as the food crusts were not buried afterformation, the base-soluble fraction is of course not soil-derived humic substance. Instead of this, it consistsprobably of fatty acids. The solubility of the wild boar food crust in NaOH points to incomplete carbonisationof the sample. In future experiments, the time for letting the crust char should therefore be longer to checkif this increases the fraction which is not base-soluble. The table shows that there is no significant differencein the pretreatment yield of the archaeological and modern samples. This is an indicator for the reliabilityof food crusts as sample material. Apparently, the food crusts only disintegrate to a limited extent in thesoil. Later, for some of the food crusts, the same method as for bones was tried (protein-extraction), but theyield was too small: From 534.5 mg food crust of sample SID 12056 (wild boar), only 2.6 mg protein couldbe obtained. That is a pretreatment yield of 5 mg per g original sample mass. Only half of it, 1.3 mg, couldbe taken out of the glass. The fish food crust SID 12058 yielded approximately the same protein ratio. From282.2 mg sample, 1.7 mg proteins could be extracted. This corresponds to a yield of 6 mg per g originalsample. Here, only 0.3 mg could be taken out of the glass after pretreatment, as the rest of the extractedmaterial was adhering to firmly to the glass. Pretreated food crusts consists usually of about 50% carbonso that the yield can also be expressed as around 3 mgC per gram sample. These yields are only slightlyhigher than the protein yields that were reported for archaeological food crusts that were extracted with the“Lowry”-method (see section 1.4. With that method, 1 mg carbon could be obtained from 1 g of food crust.Assuming that the “collagen” yield is smaller for archaeological than for modern samples, protein extractionis not the right method of pretreatment for radiocarbon dating. For obtaining sufficient carbon masses withthe protein extraction method, big food crust samples are needed. However, only few sides provide foodcrust samples with masses of several hundred mg. For radiocarbon dating, other methods have to be appliedthat give a higher carbon yield.For stable isotope analysis, though, where the required sample masses aresmaller, one could assume to use this method of protein extraction. Further research on the recent foodcrusts is planned to test several methods of food crust pretreatment and to compare the 13C and 15N valuesthat are obtained after these different pretreatments.

Some authors prefer not to pretreat food crusts for δ13C and δ15N measurements at all because thepretreatment has no influence on for example the δ13C value whereas it is possible that part of the foodcrust dissolves under pretreatment (Craig, Forster, Andersen, Koch, Crombe, Milner, Stern, Bailey, andHeron 2007). For radiocarbon dating, though, I chose to pretreat the food crusts as already minor amountsof modern contamination can alter the age of the sample significantly. Hallgren and Possnert (1997) reportthat the chemical pretreatment of organic remains on neolithic potsherds yielded almost no insoluble fraction.This means that the degree of carbonisation (particle content) was small and that the biggest part of theorganic remains is connected to alkalisoluble compounds, probably lipids. It has been shown that the alkali-soluble and alkali-insoluble fraction of a food crust have about the same age (Segerberg, Possnert, Arrhenius,and Liden 1991).

Instead of scraping off the food crusts from the sherd, it is also possible to crush the whole sherd andplace it in deionized water so that the minerals sink to the bottom and the organic remains float on thesurface (Johnson, Stipp, Tamers, Bonani, Suter, and Wolfli 1986). This method has not been applied in thiscase, because it makes only an analysis of the whole organic material from the sherd possible: the total ofanimal fats, plant fibres, charcoal used in the tempering process (Johnson, Stipp, Tamers, Bonani, Suter,and Wolfli 1986), and soot deposits in the pores. In this case, specific analyses of food crusts were desiredso that the crust alone had to be removed carefully from the sherd. Another disadvantage of crushing thesherd to extract the organic material is that the sherds are completely destroyed in that way.

4.1.5 Bone

Before describing the chemical pretreatment that is applied to bones in our laboratory, I will explain whichsubstances are present in the bone and how they are affected during burial. The chemical pretreatmentprocedure will be described and methods of quality control will be presented, for examining the reliabilityof the bones as sample material for radiocarbon dating and stable isotope analysis. My samples will thenbe tested using these quality criteria. A short paragraph about the zoological appraisal of the find materialfrom Schlamersdorf will round off this section. A similar examination for the find material from Kayhude

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has not yet been done.Bone and antler consist to approximately one third of organical primary substance (ossein and fat)

and to two thirds of inorganical material (85% of it calcium phosphate, furthermore calcium carbonateand calcium fluoride). On the soil surface and in well-aerated/ventilated soils (like sand or gravel), bonesare not preserved: microbiological processes degrade organical substances and the silicid acid in the sanddissolves mineral substances. In contrast to that, the preservation conditions for bone are excellent in humidsediments from lakes and bogs or in submarine settlements. Only in high moors the high acidity (pH upto 2) dissolves the mineral substances (Dellbrugge 2002). It is expected that the organical substance ofthe bone changes least during deposition in the soil. Therefore, the bone pretreatment method is proteinextraction, or “gelatinisation”. The extracted substance (proteins) is often referred to as collagen, althoughit is well known that the degraded bone material is different from the original collagen (Kanstrup 2008). Asbone substance consists in the average of bigger molecules than contaminants from the soil, the extracteddissolved “collagen” is ultra-filtered to exclude the small-molecular contaminants. The >30 kDa (Da =Dalton) fraction is used for dating and isotope analysis.

If the bone pieces are big enough, bone powder is drilled out of the bones after rinsing the surface of thedrilling area. Between 200 and 300 mg powder are normally used. If the bones are too small to allow drilling,for example fish bones or small bone fragments, they are cleaned in demineralized water and ultrasound.After that, they are either cut into small pieces, smashed with a hammer or mortared. The first step in thechemical bone pretreatment procedure is the decalcification, that is the removal of inorganic material. Thebone powder is cooled down to 5◦C and 1M HCl, also cooled down, is added. The bone powder - acid mixtureis stirred regularly and kept in a fridge at 5◦C until the bubbling stops. After the bubbling has stopped(usually after 15-20 minutes), pH is controlled. If the pH is >0.5, more acid is added. When the bubblinghas stopped again, the pH is controlled and if necessary, more acid is added. This has to be repeated untilthe pH is <0.5 when the bubbling has stopped. The low temperatures are needed to prevent the proteinsfrom dissolving. After 3 to 5 minutes in the centrifuge at 2000 rounds per minute (rpm), the solution ispoured off and the sample is rinsed with demineralized water. 0.2M NaOH is added at room temperatureto dissolve humic acids that entered the samples from the soil. After 15 minutes, the colour of the solutionis controlled. When it is very dark, new NaOH is applied to the sample. This is repeated until the solutionis almost clear. After pouring off the NaOH solution and rinsing with demineralized water, 10−2M HCl isadded to the samples so that the pH is between 2.0 and 2.5. The pH is controlled after 30 minutes andHCl or demineralized water is added, if needed, until the pH is stable at 2.0 - 2.5. Then the samples areplaced in a heating cabinet at 58◦C over night to extract the “collagen”. The ultrafilters Amicon Ultra 4mL,>30 kDa, LOT-number R4JN69709 were used for the samples discussed in this thesis. They are cleanedfirst with filling them with water and centrifuging them two times with fresh demineralized water, thenwith demineralized water in the ultrasonic bath and again centrifuging three times with fresh demineralizedwater. On the next day, the gelatin solution is poured into the ultrafilters. Insoluble residues on the bottomof the reaction tubes are kept down using centrifugation and 5-8 µm Ezee mesh filters (Elkay LaboratoryProducts) which have been cleaned with ultrasound and demineralized water. The gelatin solution is nowultrafiltered (7 minutes at 3500 rpm) to remove small molecules. After ultrafiltration, the gelatin solution ispoured into new, weighed glasses. They are cooled down, frozen with liquid nitrogen and finally freeze-dried,which takes one to two days. The glasses containing the “collagen” are weighed to calculate the collagenmass and estimate the collagen yield.

To determine the chemical integrity of the extracted gelatin, the C:N ratio, the mass ratio of carbon versusnitrogen, can be used. Bonsall, Cook, Hedges, Higham, Pickard, and Radovanovic (2004) define a range ofacceptability between 2.9 and 3.6. This range can be refined to between 3.1 and 3.5 for radiocarbon dating(Kanstrup (2008), and references therein). Also the gelatin (“collagen”) yield can be used as a criterion ofthe sample’s quality. Bonsall, Cook, Hedges, Higham, Pickard, and Radovanovic (2004) for example do notroutinely date yields below 10 mg collagen per g sample. The demands on collagen yield were reduced innewer literature, so that a yield of 1 mg g−1 is sufficient for some groups (Kanstrup 2008). For samplesprepared without ultrafiltration, yields above 3.5% (35 mg g−1) are required. In table 4.2, the gelatin yieldand C:N ratio for all pretreated samples is shown. There was not enough material from some of the samples

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for both 14C dating and stable isotope measurements. Some of the samples were kept to be combusted inthe EA for 13C and 15N measurements with additional CO2 trapping for graphitisation and 14C dating whenthe new trapping device is tested well enough to allow the processing of archaeological samples. Some of thesamples were only graphitised for 14C dating.

Table 4.2: Quality of extracted “collagen”. For samples without C:N ratio: † not enough material for EA,only cathode for 14C dating; ? material kept for on-line combustion at EA with CO2 trapping.

SID Find Sample material Sample size (mg) Pretreatment yield C:Nnumber before after (mg collagen ratio

pretreatment per g sample)12060 (Trave) Fresh fishbone 108.4 11 102 3.112097 (Trave) Fresh fishbone 94.9 12.3 130 3.112099 SLA5-2784 Bone (wild cat) 296 7.2 24 3.212100 SLA5-2761 Bone (beaver) 220.1 2.1 9 3.612101 SLA5-2883 Bone (wild boar) 299.3 5.3 18 3.212102 SLA5-2913 Fishbone 373.4 1.5 4 ?12154 (Alster) Fresh fishbone 341.4 18.3 54 3.212167 SLA5-2869 Fishbone 406.2 5.8 14 ?12342 SLA5-2786 Tooth (red deer) 226 6 27 †12343 KAY8-815,0 Bone 616 6.3 10 †12344 SLA5-2874 Tooth (aurochs) 509 4.3 8 †12392 (Kayhude) Fishbone (pike) 254.9 2.8 11 †12393 (Kayhude) Fishbone (pike) 146.2 0.13 10 †12606 SLA5-2912 Fishbone 145.2 3.7 25 †12608 SLA5-2906 Fishbone 103.0 3.1 30 †505 Background bone 183.1 7.9 43 . . .505 Background bone 180.5 6.3 35 . . .

From the two background bone samples, no “collagen” was taken for stable isotope measurements, butthe C:N ratio for other samples of the same background bone material is about 3.3. The two backgroundbone samples were pretreated with different methods: the first with ultrafiltration and the second without.Apparantly, the collagen yield for the background bone sample prepared with ultrafiltration is bigger thanthat for the sample without ultrafiltration. This fact is hard to explain because one would expect that theyield is smaller for those samples where a fraction of the molecules is removed (ultrafiltration removes smallmolecules). As these are only two samples and as the difference is not very big, statistical errors could be thereason. While being weighed, the samples can uptake water from the air, depending on the time they areexposed to air and on air humidity. It could therefore be that the one sample has incorporated more waterand so became heavier than the other. All samples for which C/N measurements were available lie in the“range of acceptability” Bonsall, Cook, Hedges, Higham, Pickard, and Radovanovic (2004) defined for C:Nvalues. The collagen yield varies a lot between the different samples. Modern samples yield most collagen:between 54 and 130 mg collagen per g sample. This was expected because no collagen degradation couldtake place in those samples. The high yield of background bone samples (35 and 43 mg/g) is consistent withlaboratory experience. The background bone samples are taken from well-preserved whale bones and alwayshave quite high collagen yields, compared to other archaeological bone samples. The collagen yield fromarchaeological samples ranges from 4 to 24 mg/g. Three of the samples, a bone (beaver), a tooth (aurochs)and a fishbone sample from Schlamersdorf, had a collagen yield that was defined as not sufficient by Bonsall,Cook, Hedges, Higham, Pickard, and Radovanovic (2004). For the tooth sample, a low collagen yield wasexpected because it was not clear how much of the material drilled out from the tooth contained collagenand how much was tooth enamel, for example. For the other tooth sample, it was possible to use only the

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collagen containing parts, so that the collagen yield is quite high. The low collagen yields of the beaverbone and fishbone samples can be explained by the advanced decomposition of these bones. Because of thelimited amount of bone samples from the sites and because the C:N ratios are in the range of acceptabilityfor all samples with C/N measurements, it was decided to use all the samples listed in the table above fordating, although the collagen yield for some of them is quite low.

Bone from Schlamersdorf

For the bones from Schlamersdorf, a detailed zoological analysis is available. Some of the bone findings fromSchlamersdorf have a dark colour because of humic acid. They are not very well preserved and especiallymost of the fish bones are porous and crumbly. All bones were found in the former littoral, i.e. in the wastezone of the settlement. This is certainly caused by the different preservation conditions: in the shallowwater, the bones were better preserved than on the well-ariated soils of the settlement site. There is a largenumber of species, but only a small number of individuals per species. Of the 389 bone findings, 288 couldbe determined and belonged to 33 species. But not all of these have been hunted by humans. Especiallysmall mammals and very small fish did probably not belong to the range of prey species of prehistoric manbut were washed ashore. With the species that might have belonged to the human prey spectrum, onealso has to be careful because also they can be natural depositions. The small number of bone findings ofanthropogenic origin leads to the conclusion that this site has only been inhabited temporarily. Also thetransportation of the prey to a probable main settlement a bit further away could be the reason. There havealso been flint tools but no evidence for the production of these flint tools (Heinrich 1993), which also pointsto the existence of a bigger settlement nearby, so that the production of flint tools was not necessary in thiscamp.

The species that probably were fished/hunted by humans are the following: Northern pike (Esox lucius)gave most fish bone findings: 111 from at least 5 individuals. There are also 38 findings of cyprinids(Cyprinidae), with at least 5 individuals, and 38 of European perch (Perca fluviatilis), with at least 7individuals. The comparatively high number of cyprinids is consistent with their availability in the river(Heinrich 1993). Also the Northern pike has been important for prehistoric fishing in middle and northernEurope, although it can be expected that it is overrepresented in the archaeological record because of thehigh resistance of its bones (Heinrich 1993). The same effect can be expected for perch bones, because theyare also more resistant than some other bones. Especially the very small ones could be taphocoenotic. Therewere bones from at least 11 individuals of waterfowl and 1 wild boar, 2 red deer and one aurochs that alsomay have been hunted for meat. Some smaller mammals like wildcat, European otter, European beaver andred squirrel may have been hunted for their fur. A quite big number of different mice can best be explainedwith the ideal life conditions for these species in the surroundings of the site (Heinrich 1993).

4.2 Dating and stable isotope measurement results

First, a wide selection of recent material has been dated in order to ascertain the hardwater effect and tostudy the changes in age when going from water samples to fish and molluscs and finally to food crusts. Thelatter examinations have mainly been conducted on material from the river Trave. Samples from the riverAlster have only been examined to see if a hardwater effect is existent in that river. It is assumed that thewater and fish from one river have too high ages that can also be found on food crusts from this material. Thisleads to the conclusion that also food crusts from material from another river show too high ages, if its waterand fish show the high ages. Therefore, it is not necessary to make food crust experiments with material fromboth rivers. Although both sites are described as shortly-occupied hunting stations, it can not be concludedthat all the material found there was contemporaneous. There is a possibility that the hunting stations wereused several times within intervals of some centuries. For being sure that only contemporaneous material iscompared, groups of associated finds were chosen. These are fish bones compared with bones of terrestrialanimals to find out if the hardwater effect was existent in the archaeological material. Furthermore, foodcrusts are compared with terrestrial material such as wood, charcoal or bones of terrestrial animals. In the

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case of Kayhude, these are finds from one stone layer which seems to be undisturbed by fluvial processes likeinundation or sedimentation. In the case of Schlamersdorf, the coordinates of the samples were comparedand samples from the same layer and similar position were grouped.

The results of the 14C measurement are given in percent modern Carbon pmC and in 14C age, in yearsBP. The 14C age is calculated from the pmC in the following way:

14C age = −8033 lnpmC100

(4.1)

4.2.1 Recent samples from the river Trave

The first datings on samples from the river Trave were conducted on four modern samples: One watersample, one fresh fishbone, one food crust made from fresh fish from the Trave and one food crust made offresh wild boar meat.

Table 4.3: Trave - modern samples

Sample ID Sample material pmC 14C age Date cal. AD(years BP) (95.4% interval)

12504 water 86.54±0.57 1170±55 695-698 (0.3%),708-747 (6.0%),766-987 (89.1)

12060 fresh fish bone 96.51±0.38 284±32 1492-1603 (60.9%),1614-1665 (33.4%),1785-1793 (1.1%)

12097 fresh fish bone 97.00±0.34 244±28 1525-1558 (6.9%),(cooked) 1631-1680 (56.4%),

1763-1801 (26.1%),1938-1955 (6.0%)

12058 food crust (fresh fish) 96.11±0.31 371±23 1487-1645 (95.4%)12055 food crust 106.87±0.45 -537±34 1956-1957 (4.0%),

(fresh boar meat) 2002-2008 (91.4%)

In table 4.3, the 14C content is given in percent modern carbon (pmC) as well as the calibrated AD-ages.The data was calibrated with OxCal 4.0, using the calibration curve IntCal04. The development and use ofa calibration curve is described in section 1.1.3.

It can be seen from the data that the fresh fish bone has nearly the same age as the food crust which wasprepared from the meat of the same fish. It can therefore be concluded that in the archaeological material,food crusts and fishbones should show approximately the same age, if the food crust was made exclusivelyfrom fish. It is noticeable that the age of the water is much higher than that of the fish and the fish foodcrust. The fish should show the same age as the water if the fish feeds on water plants and water animals. Itis known that roach also eat insects, but their diet consists mainly of freshwater organisms. The nutrition ofthe roach is therefore not a sufficient explanation for the difference in ages between water and fish. Anotherreason could be that there are water plants in the river that take carbon not only from the river waterbut also from the atmosphere so that their 14C concentration is not so depleted as that of the river water.The most probable reason, though, is that only dissolved inorganic carbon (DIC; see section 1.2.3) but notdissolved organic carbon (DOC) is dated with the method I applied while fish and other water animalsuptake carbon from both sources. It would therefore be interesting to also date DOC, which should have ayounger radiocarbon age if the above reasons really can explain the age difference between water and fish.

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It is desirable that in the future, both fractions of dissolved carbon are dated and not only the dissolvedinorganic carbon. As DOC is not routinely dated in our laboratory, the efforts of extracting the DOC fromthe water samples would have been too big for examining the DOC in this work, as the DOC extraction isdescribed in the literature as being complicated and time-consuming (see section 1.2.3). For future work,DOC extraction of the already collected water samples from both rivers is planned. It is expected that theaverage age of DIC and DOC corresponds to the radiocarbon age of the fish.

Furthermore, the seasonal changes of the water hardness and of the DIC’s and DOC’s 14C concentrationhave to be taken into account, although the effect is expected to be smaller in rivers than in lakes. Asexplained in section1.2.3, biologic activity removes CO2 from the original DIC reservoir so that more exchangewith atmospheric CO2 can take place. This increases the 14C value of the DIC as dissolved CO2 is one ofthe DIC species. Seasonal changes of the exchange ratio with atmospheric CO2 can thus not explain thedifference between the 14C ages of the fish and the DIC. For future examinations of the hardwater effect,several water samples should be taken throughout the year. Both DIC and DOC from these samples shouldbe dated and compared with the 14C age of water plants and fish. The δ13C value for the Trave water sampleis -13.59±0.01hwhich is a normal value for groundwater DIC. The δ13C value for the Trave water is thusreasonable as rivers usually originate from groundwater (see section 1.2.3). The surprisingly high DIC ageof the Trave water could be due to the precipitation of secondary calcite, a process which dilutes the 14Cwithout being visible in the δ13C value (Clark and Fritz 1997).

The age of the wild boar food crust is out of the range of the calibration curve: it is too young to appearon the curve. For a calibration of the wild boar food crust, the calibration curve has to be extended topresent using an exponential decay curve, as the 14C concentration from H-bomb testing in the atmospheredecreases exponentially (see page 4). Therefore, an exponential decay curve has been fitted to the data ofthe bomb pulse calibration curve “Kueppers04” used by OxCal. “Kueppers04” was obtained by 14C datingof tree-rings from 1890 to 2001. The 14C data in calibration curve data is given as ∆14C and 14C age inyears BP. ∆14C is defined byStuiver and Polach (1977) as

∆14C =(

ASN

AABS− 1

)1000h. (4.2)

AABS is the 14C activity of the standard material oxalic acid, corrected for decay since the time of the firstmeasurement of this standard (see also section 1.2.1):

AABS = AONeλ(y−1950) (4.3)

with the standard oxalic acid activity AON and the year of measurement y. λ denotes in this case the “real”radiocarbon decay constant of 1

8267a which belongs to the half-life of 5730 a (Stuiver and Polach 1977). Theradiocarbon age of a sample is given as

t = −8033 ln(

ASN

AON

)(4.4)

where 8033 a is Libby’s radiocarbon mean life. The curve has been fitted to the data given in ∆14C from1985 to 2001 because there the exponential decrease was most pronounced. The calibration programme usesthe data given in radiocarbon ages (t) so that the radiocarbon age had to be calculated from the ∆14C valuesin the following way:

t = −8033(

ln[

∆14C

1000h+ 1

]+

18267a

(y − 1950))

(4.5)

The data obtained in this way was merged with the data of the Kueppers04 calibration curve to form a newbomb pulse calibration curve reaching to the present. In figure 4.2.1, the data from Kueppers04 and theexponential decrease fit are shown.

The obtained calendar age in the 95.4% probability range is 1956 to 1957 (4.0%) and 2002 to 2008(91.4%). This fits well with the assumption that the wild boar meat was, although frozen, quite fresh whenwe bought it in summer 2007. The exponential function fitted to the Kueppers04 calibration curve is only

85

Figure 4.6: The bomb pulse is extended via fitting an exponential decrease function to the data.

86

an approximation. We set the offset of the ∆14C exponential curve to zero and this is not totally correct.As a first approximation, one could assume that when the effect of the bomb pulse is totally faded out, the∆14C, which is the difference of the sample’s 14C activity and the 14C activity of the standard oxalic acid,would be zero for contemporary samples. The activity of the oxalic acid standard was determined in a yearin which the effect of the bomb pulse already began and the Suess effect depletes the 14C activity of samplesin the near future to an unknown extent, depending on the amount of fossil fuel that then will be burnt.Therefore, it is impossible to exactly define an appropriate offset.

Because of the influence of the bomb peak, it is hard to directly calculate modern reservoir ages. Whencalibrating the measured 14C age, the calibrated age would underestimate the reservoir effect. Therefore,the age difference is calculated from the 14C ratio in percent modern carbon and from this difference thereservoir age is calculated. With the 14C ratio F (pmC) of the riverine sample, the 14C ratio F0 of theterrestrial sample and the mean life of 14C τ=8033 a or 8267 a, the reservoir age ∆t can be calculated as

∆t = τ(ln F0 − ln F) = τ lnF0

F(4.6)

Two different reservoir ages can be calculated, depending on which mean life of 14C is taken. If the reservoirage is to be expressed in 14C years, the mean life 8033 a belonging to Libby’s radiocarbon half-life has tobe taken. For an estimation of the reservoir effect in kalender years, the mean-life of 8267 a belonging tothe “real” half-life of radiocarbon, 5730 a, is used. In the case of recent samples, F0 is the pmC of theatmosphere at the moment of taking the samples from the river (that is, summer of 2007). The atmospheric14C content is constantly monitored on the mountain Schauinsland in the Black Forest near Freiburg imBreisgau, Germany, and in the high Alpine research station Jungfraujoch in Switzerland. In summer 2007,the atmospheric 14C concentration measured at these two sites was between 105 and 105.5 pmC.

Table 4.4: Trave - reservoir ages of modern samples

Sample ID Sample material Reservoir age (14C years) Reservoir age (years)12504 water 1585±62 1631±6312060 fresh fish bone 701±46 722±4712097 fresh fish bone (cooked) 660±40 679±4112058 food crust (fresh fish) 734±40 756±41

4.2.2 Archaeological samples from Schlamersdorf (Trave)

Associated samples of both fluvial and terrestrial origin have been dated. The difference in radiocarbon ageof paired samples is the reservoir age. Only one food crust sample, SID 12349 from Schlamersdorf yieldedenough carbon to be dated using the old ion source. Unfortunately, the graphite of this sample fell out inthe ion source and could thus not be measured. Therefore, only the date for a plant rest that was foundinside the sherd is available. This plant rest could have entered the sherd during the production process ofthe pot. In that case, it would almost be contemporaneous with the formation of the food crust. It couldalso be a rootlet that grew through the sherd during its deposition in the soil. In that case, the plant restwould be a terminus ante quem for the formation of the food crust. It was originally planned to date bothsamples from the same sherd, the food crust and the plant rest. With the loss of this food crust sample,the only food crust sample that was datable with the old ion source was lost. The other food crust samplescan first be dated when the new ion source is tested and running fine, so that they can not be considered inthis thesis. Of the three sherd samples that are left, one had both an outer and an inner crust as well as aplant rest inside the sherd. This is another possibility of comparing different samples from the same sherd.

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They are expected to be contemporaneous if the plant rest was incorporated during the pottery productionprocess. The outer crust may show a higher age: It could consist of soot that derived from old wood in thehearth fire. Stable isotope measuerements were done for a number of food crust samples from Schlamersdorf.The results of these measurements will be presented in section 4.3 where they are compared to the stableisotope measurements of samples from Kayhude, Neustadt (see section 4.2.5), and modern samples.

Table 4.5: Trave - archaeological samples

Sample ID Sample material pmC 14C age (years BP) Date cal. BC (95.4% interval)12099 Wildcat 49.28±0.19 5675±31 4601-445412101 Wild boar 47.18±0.34 6031±58 5205-478112051 Burnt wood (1) 48.89±0.56 5747±92 4796-437012051 Burnt wood (2) 46.15±0.29 6211±51 5306-503612051 Burnt wood (3) 46.18±0.36 6206±62 5309-500412100 Beaver 44.61±0.50 6484±90 5617-530612349 Plant rest from sherd 47.47±0.31 5982±52 4999-472912342 Red deer 45.79±0.38 6270±66 5463-505012606 Fish 38.64±0.38 7638±80 6646-637212608 Fish 38.73±0.56 7617±115 6697-6227

In figure 4.2.2, the samples dated so far are shown. Please notice that there are three datings from thewood sample SID12051. This sample is burnt wood from the find layer. The first date was obtained withthe old ion source and a normal sample size. The two other dates were made with the new ion source. Thesample sizes were small, and the graphitisation took place in small reactors. These two samples were testsamples for the new ion source. The results from these samples are not reliable and are therefore excludedfrom further discussion. Figure 4.2.2 shows that the results of the two small samples match perfectly. Thereis a significant difference, though, between the dates of the smaller samples and the date of the normal-sizedsample.

When interpreting the result of SID 12100, beaver bone, one has to keep in mind that the pretreatmentyield of this sample was very low. It is therefore less probable that the accurate age of this sample ismeasured. This could explain why the age of the beaver is much higher than for example of the wood sampleSID 12051 of the wildcat SID12099. A few of the samples were clearly associated when excavated. Whenchosing the samples for dating, it has been paid attention to grouping food crusts with terrestrial samplesor fluvial with terrestrial samples. All food crusts and all but two fishbone samples could not be dated.Therefore, only few “pairs” are left for interpretation. Samples were regarded associated when they camefrom the same depth level and the horizontal distance between them was small enough, in most cases a fewcentimeters. Two samples that were clearly associated are SID 12099 wildcat and SID 12051 burnt wood.Figure 4.2.2 and table 4.5 show that these two samples are contemporaneous in the range of errors. Thetwo dated fishbone samples SID 12606 and SID 12608 were found closely next to each other. They haveaccordingly an equal age as can be seen in figure 4.2.2. These two fishbone sampels were found associatedwith a plant rest from the sherd SID 12349 and with the red deer tooth SID 12342. The age differencebetween the fish bones and the red deer tooth is probably due to the reservoir effect. Two dual inlet δ13Cmeasurements of the red deer tooth are available: δ13C = -23.63±0.01 and δ13C = -23.54±0.01. As thesetwo δ13C values were obtained from samples that were pretreated and combusted independently and as theδ13C values are terrestrial, the sample’s 14C value is also being regarded as reliable. The fish bone SID12606 has a δ13C value of -26.78±0.01, measured with dual inlet. In section 1.3.1, δ13C values for freshwatersystems were given: At the end of freshwater food chains, δ13C values in bone collagen are expected to bebetween -24h in lowland rivers and -20h in lakes and canals. The Trave is a lowland river so that δ13C

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Figure 4.7: The calibration of the archaeological samples from Schlamersdorf.

89

values of about -24h are expected here for the end of the fooc chain. The δ13C value increases along thefood chain. The fish SID 12606 and SID 12608, the one being a member of the cyprinid family and the otherone unknown, but of similar size, are quite small and were thus not at the end of the food chain. The δ13Cvalue measured for SID 12606 fits thus well into the expectation: It is more negative than the δ13C valueone would expect for the end member of a food chain. Therefore, also the dating of SID 12606 is regardedUnfortunately, there was not enough material to allow continuous flow carbon and nitrogen stable isotopemeasurements of the red deer tooth and these two fishbones.

4.2.3 Recent samples from the river Alster

Three recent samples from the Alster have been dated: one water sample, one snail-shell from a water snailthat was collected alive in the river and bones from a fish that was caught in the river.

Table 4.6: Alster - modern samples

Sample ID Sample material pmC 14C age Date cal. BC/AD(95.4% interval)

12503 water 78.28±0.32 1966±33 44BC-87AD (92.7%),106AD-120AD (2.7%)

12154 fresh fish bone 97.27±0.35 222±29 1641-1684 AD (38.9%),1736-1805 AD (43.3%),1935-1955 AD (13.2%)

12153 snail-shell 94.75±0.37 433±32 1418-1498 AD (91.6%),1601-1615 AD (3.8%)

The reservoir age of the river water from the Alster and the samples from this river is calculated afterequation 4.6. The reservoir age in 14C years is calculated using Libby’s radiocarbon mean life of 8033 yearswhile the reservoir age in years is calculated using the “real” radiocarbon mean life of 8267 years. Whencomparing table 4.6 with table 4.7, one can see that the calibration of the measured data leads to wrongestimates of the reservoir age. The water sample, for instance, has after calibration an age of a little lessthan 2000 years, whereas the reservoir age for this sample is 2380 14C years or about 2450 calendar years.

Table 4.7: Alster - reservoir ages for modern samples

Sample ID Sample material Reservoir age (14C years) Reservoir age (years)12503 water 2380±44 2449±4512154 fresh fish bone 635±46 653±4612153 snail-shell 844±46 868±47

Also in the Alster, the reservoir age of water and fish bone / shell differs significantly. A possibleexplanation can also here be that the water is only dated using DIC while fish and snail could also incorporateDOC.

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4.2.4 Archaeological samples from Kayhude (Alster)

Unfortunately, two bone samples from Kayhude could not be dated. The size of these samples was too smallfor measurements with the old ion source. Therefore is it only possible to compare the three food crust dateswith charcoal, as this was the only certainly terrestrical sample. The reservoir age ∆t is calculated afterequation 4.6. This is the same as substracting the age of the terrestrial sample from the age of the fluvialsample. Some samples from Kayhude have already been 14C measured at the Leibnitz Laboratory for AgeDetermination and Isotope Research, Christian Albrechts University Kiel. The results were kindly placed tomy disposal by Ingo Clausen,

Table 4.8: Alster - archaeological samples

Sample ID Sample material pmC 14C age Date cal. BC(95.4% interval)

12047 Food crust 49.23±0.47 5692±54 4706-436712048 Food crust 46.84±0.46 6088±56 5221-479912345 Food crust 51.35±0.68 5349±106 4501-380012346 Charcoal 50.82±0.26 5437±41 4359-417712392 Fishbone 34.64±0.61 8514±83 8165-7177

Sample ID (KIA) Sample material pmC 14C age Date cal. BC(95.4% interval)

29523 Wooden pole (alder) 47.95±0.23 5905±40 4893-469429524 Wooden lance (hazel) 50.89±0.19 5425±30 4341-423929525 Wooden pole (alder) 47.02±0.18 6060±30 5053-484929526 Wooden pole (alder) 46.82±0.20 6095±35 5207-491129527 Food crust 44.89±0.17 6435±30 5476-534129527 (humic) Food crust 43.88±0.17 6615±30 5620-549029528 Wooden pole (hazel) 54.92±0.19 4815±30 3654-352630079 Wooden axe handle (hazel) 45.86±0.20 6265±35 5320-507830080 Wooden axe handle (ash) 51.31±0.19 5360±30 4327-40559906 T-axe (antler, red deer) 49.12±0.26 5710±40 4684-4459

In this case, the fishbone, SID 12392, is about 3100 14C years older than the charcoal sample, SID12346.If assuming that they were deposited at the same time, the reservoir age for samples formed in the Alster isabout 3100 years during the Ertebølle period. In figure 4.2.4, the calibrated samples both from our laboratoryand from Kiel are shown.

The figure shows that the food crust that was dated in Kiel is older than the three food crust samples thatwere recently dated. The wood samples show a great variability. Two of them, KIA29524 and KIA30080 areapproximately contemporaneous with the charcoal sample. It should be kept in mind, though, that KIA30080was reported to give a small pretreatment yield and that the result should be interpreted with caution. Ifthe wooden pole KIA29528 is regarded as an outlier (due to contamination or disturbed stratigraphy), allother wooden poles are contemporaneous with or older than the charcoal sample. A possible scenario isthat the wooden structure of poles was constructed at the same time as the charcoal was used. The higherages of some of the wood samples may be the result of the usage of old wood for the wooden structure.The fishbone sample is significantly older than all the other samples from Kayhude that were measured upto now. If assuming that the fishbone sample and the food crusts were formed at about the same time,it can be concluded that the food crusts were not exclusively made of fish. The experiment with recentfishbones and food crusts made from the same fish showed that both samples yielded about the same age

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Figure 4.8: The calibration of the archaeological samples from Kayhude. SID number: sample was measuredat the AMS 14C Dating Centre, Aarhus University. KIA number: sample was measured at the LeibnitzLabor for age determination and isotope research, Christian Albrechts University Kiel.

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Table 4.9: C/N data of archaeological food crusts from Kayhude and modern food crusts

Sample ID Material C:N δ13C δ15N12047 Archaeologic 8.71 -28.88±0.10 6.96±0.0912047 Archaeologic 9.31 -30.72±0.10 6.06±0.2512047 Mean Value 8.76±0.30 ± ±12048 Archaeologic 9.05 -28.70±0.10 11.41±0.0912048 Archaeologic 9.05 -28.79±0.10 10.33±0.2512048 Mean Value12345 Archaeologic 17.44 -26.44±0.10 1.50±0.0912345 Archaeologic 17.89 -26.62±0.17 3.8±0.25

12055 Wild boar (humic) 6.40 -17.88±0.10 7.95±0.0912055 Wild boar (humic) 6.40 -17.80±0.10 7.31±0.2512056 Wild boar (humic) 6.91 -18.00±0.10 7.83±0.0912056 Wild boar (humic) 6.85 -17.92±0.10 6.67±0.2512057 Fish 6.29 -27.21±0.10 17.58±0.0912057 Fish 5.87 -27.55±0.10 16.55±0.2512058 Fish 5.31 -28.14±0.10 18.02±0.0912058 Fish 5.72 -28.74±0.10 17.93±0.2512058 Fish (humic) 6.73 -123.25±0.10 18.25±0.0912058 Fish (humic) 7.42 -30.74±0.10 17.43±0.25

KIA29527 Archaeologic . . . -28.86±0.22 . . .KIA29527 Archaeologic (humic) . . . -28.34±0.09 . . .

(see section 4.2.1). As the food crust samples have about the same or a slightly higher age than the charcoal,it can be concluded that they consist mainly of terrestrial ingredients with a little freshwater component.Stable isotope measurements can shed more light on the composition of the food crusts. Unfortunately,no stable isotope analysis was available for the food crust sample dated in Kiel. Only the result of a 13Cmeasurement at the accelerator can be given. This result is only to a limited extent comparable with otherstable isotope measurements as it is influenced by fractionation during graphitisation and in the ion source.

The modern food crusts SID 12055 and 12056 dissolved completely in the NaOH step, so that only the“humic” fraction was used. The similarity between the 13C values of the archaeological food crusts to thoseof the modern fish food crusts is striking.

4.2.5 Comparison with marine samples

To be able to give a short remark on marine samples, a pair of modern samples as well as one archaeologicalsample, a food crust on pottery from the coastal site Neustadt (Holstein), have been examined. The blubberof a porpoise that was found at the North Sea coast of Schleswig-Holstein was dated, as well as the crustthat was formed in a pot when the oil was cooked out of the blubber. These are the dating results:

Sample ID Sample material pmC 14C age (years BP)12394 blubber 107.40±0.38 -573±2812395 charred crust made of blubber 116.52±0.39 -1228±27

The pmC values of the porpoise are over 100% modern so that a calibration of the ages has to be donewith the bomb pulse. As the atmospheric bomb pulse is not directly reflected in the sea water, a marine

93

Figure 4.9: The bomb pulse in the atmosphere and different parts of the oceans. After C. R. Weidman,unpublished PhD thesis 1995.

calibration curve has to be applied. There are different calibration curves for various zones of the oceans.Some examples can be seen in figure 4.2.5 where also the two porpoise samples (fat and charred crust) areplotted.

It is not possible to chose one curve for the calibration of the porpoise samples because it is not clearwhere the porpoise lived and what it fed on. The calibration curves themselves were made from the 14Cdating of shells which ideally reflect their environment because they are not as mobile as fish or, for example,porpoises.

There is a remarkable difference in the 14C ratios of both samples, although they were derived fromthe same material. The difference corresponds to approximately 655 14C years (after equation 4.6). Ascan be seen from figure 4.2.5, a high pmC can be found some decades BP, while a pmC of 107 fits intothe extrapolation of the North Atlantic / North Sea calibration curves. Apparently, the 14C content of theblubber and the crust that was formed in the pot when the oil was cooked out of the blubber are different. Apossible explanation could be the following: Blubber consists of fat cells which are filled with oil. When theoil is being cooked out of the blubber, the cell rests remain at the bottom of the pot and are likely to charthere while the liquid oil can be poured out of the pot. When now assuming different turnaround times forthe fat cells and their content, so that the cells have higher average ages, an age difference for the total fattytissue and the charred crust is probable. In future experiments with blubber, both the charred crust andthe oil should be dated to test this assumption. Unfortunately, no bones from the porpoise were available.

94

This would else be the ideal material for 14C dating as it reflects the past 10 years of the porpoise’s life,the turnover time for bone collagen being 10 years. Then it would also have been possible to compare theδ13C values of the bone collagen and the fat. The blubber has a δ13C value of -22.78h whereas the crustfrom the pot has a δ13C value of -19.61h, both measured with dual inlet. The crust was also measured withcontinuous flow and yielded a δ13C value of -19.4h. The δ13C value of the porpoise blubber is very negativeand unusual for a marine animal. But as was explained in section 1.3.1, different tissues of an animal canhave different δ13C values. The difference for fat and bones of an ungulate was for example 7.7h. If weassume that a difference of the same order of magnitude also can be found in the porpoise, than its boneswould have a δ13C value of -15.1h. Bone collagen for Californian porpoises has a δ13C value of around-12.6h(Chamberlain, Waldbauer, Fox-Dobbs, Newsome, Koch, Smith, Church, Chamberlain, Sorenson,and Risebrough 2005), whereas bone collagen for Northern Pacific fur seals has values around -12hat theCalifornian coast and -15hat the Western Aleutian Islands (Newsome, Etnier, Gifford-Gonzalez, Phillips,van Tuinen, Hadly, Costa, Kennett, Guilderson, and Koch 2007). It can therefore not be ruled out thatporpoises living in the northern parts of the ocean have bone collagen values around -15h. This would thenwell fit with the δ13C value of bone collagen calculated above for our example. However, these conclusionsare based on two assumptions and further investigations are therefore necessary. At least it could be shownthat a possible explanation for the unsusually low δ13C value of the porpoise blubber exists.

The food crust from a pot from a coastal site (Neustadt) has also been dated. As it was the only materialfrom that site that was dated in this thesis, it is not possible to make a statement about the marine reservoireffect in food crusts from pottery. The Neustadt sherd has mainly been used for comparing stable isotopeanalysis on different materials, als will be shown in section 4.3.

4.3 Comparison of the sites, discussion and conclustion

The 14C ages of fresh water from both rivers differ significantly. The water from the Trave is 1506±64 14Cyears old whereas the water from the Alster has a 14C age of 2380±44. The 14C age of the Trave water isthus only 63% of the 14C age of the Alster water. The water hardness is the concentration of the alkalineearth metal ions and is an indicator for the carbonate content of the water (see section 1.2.2). As the waterhardness in the Trave is higher than in the Alster (section 3.2.1), one can conclude that the water hardnessis not an indicator for the extent of the hardwater effect. The same observation was made by Fontes (1992)who warned that carbonate dissolution should not automatically be considered as an index of 14C dilution(see section 1.2.3). The DIC amount, though, that could be extracted from the water samples, is much higherfor the Alster than for the Trave sample. The conclusion should thus rather be that the water hardness isnot a good indicator for the DIC content and age of a river water sample. As only two water samples weremeasured here, more research taking multiple samples and testing several rivers is favourable. Fish samplesfrom the Trave have a mean 14C age of 701±46 and those from the Alster are about 635±46 14C years old,which is about 91% of the 14C age of the fish bones from the Trave. In figure 4.3 the δ13C and δ15N valuesof the archaeological and modern food crust samples are mapped.

The δ13C values of the archaeological samples from Schlamersdorf and Kayhude (displayed in cyan andred) are similar to those of modern food crusts made of freshwater fish (green). The δ15N values for thearchaeological samples are in general smaller than those of modern material. This is presumably caused bythe decomposition of the food crust during burial in the soil. The carbonized parts of the food crust are notattractive for microbiological organisms, in contrast to protein-containing parts. Therefore, the δ13C valuesare supposed to reflect the original composition of the food crust whereas the δ15N values are supposed tohave changed. The δ13C values of the food crust from Neustadt are widely spread, although all sampleswere taken from the same sherd. This spread already can be found in the doublets that were measuredof the different fractions. First, a part of the food crust that already fell off the sherd during storage inthe museum was pretreated. From this part, both the base-soluble and isoluble fraction were measured indoublets. Furthermore, some food crust that was adhering firmly to the sherd was scraped off, and a doubletof the base-insoluble fraction of this sample was measured. These are the δ13C measurement results of thedifferent fractions:

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Figure 4.10: δ13C (X-axis) and δ15N (Y-axis) values of food crusts.

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Sample ID Sample material δ13C12053 Food crust, fallen off -20.10±0.1012053 Food crust, fallen off -22.99±0.1012053 Food crust, fallen off (humic) -22.11±0.1012053 Food crust, fallen off (humic) -22.10±0.1012054 Food crust, scraped off -20.58±0.1012054 Food crust, scraped off -19.08±0.10

The food crust that was scraped off the sherd has less negative δ13C values than the food crust that felloff. The measurement of the first doublet is not considered as reliable as the others as there is a big differencein the δ13C values. Only the δ13C values of the second doublet, the humic fraction of the food crust thatwas fallen off, are agreeing perfectly. The δ13C values of the pottery fit very well the expected origin. Thesamples from Schlamersdorf and Kayhude, for example, are expected to consist at least partly of freshwaterfish. Their δ13C values are about the same as those of recent freshwater food crusts. The sample from thecoastal site Neustadt is expected to reflect the marine environment where it comes from. Accordingly, theδ13C values of this food crust and of a recent food crust made of porpoise match. A complete discussion of theprobability of a hardwater effect in the archaeological material is not yet possible. The few food crust thatcould be dated up to now all come from the same site, Kayhude. The sample that were dated in this project,SID 12047, 12048, 12345, 12346 and 12392, were all associated because they were found in an undisturbedstone layer. As could be seen on figure 4.2.4 in section 4.2.4, the fishbone sample from these sample groupis significantly older than the charcoal sample. One food crust is approximately contemporaneous with thecharcoal, one is slightly, but not significantly older and one is significantly older. The age difference of the“oldest” food crust and the charcoal sample is only 650 14C years, whereas the age difference between thefishbone and the charcoal is more than 3000 years. As was shown in 4.2.1, a food crust that only consistsof fish has the same 14C age as the bones of a fish that was used for preparing the crust. It can thereforebe concluded that the food crusts from Kayhude not exclusively originate from fish. If they did, then theyshould have the same age as the fish bones. It is remarkable, though, that the food crusts from Kayhudehad the same δ13C value as modern food crusts that were made of freshwater fish. It can thus not be ruledout that the one fishbone that was dated so far really is older, not only in hardwater-caused 14C years, butalso in real calendar years. In that case, it must have entered the find layer 3000 years after it had beendeposited elsewhere. As the reservoir age for modern Alster fish is about 650 years (see section 4.2.3), it isunlikely that the reservoir age during the time of the Ertebølle culture was 5 times as high. A final answerto the question “Hard water or high ages?” is not possible until the remaining samples are dated. It canonly be concluded that a hardwater effect on food crusts from Schlamersdorf and Kayhude is probable, butthe extent of the hardwater effect can not yet be determined.

The experiments concerning the preparation of small samples are not terminated, but some generaltendencies could already be observed. Iron will be used instead of cobalt for graphitisation of small samplesbecause it improves the reaction ratio. Furthermore, it could be shown that a smaller reaction volumereduces fractionation during graphitisation. Thus, the small reactors will in the future be used routinely forsamples below 0.2 mgC, and the normal-sized reactors will be exchanged with reactors that have a reducedvolume, but are still big enough for the graphitisation of about 1 mgC. These new reactors will also havepressure transducers that are connected to a computer so that the pressure can be monitored automatically,as is already is possible for the small reactors. It could be shown that the trapping device that combinesstable isotope measurements with the combustion of samples for AMS 14C dating works in principle withoutintroducing more fractionation than the traditional combustion process. Only the trapping yield is notsufficient. Further development will include the use of really vacuum-tight valves and automatisation ofthe cryogenic transfer of the sample to a manifold tube for handling the sample over to the graphitisationsystem.

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Glossary

ActivityThe activity of a radioactive substance is the number of disintegration per time unit. It can be measuredin Becquerel (1bc = 1 decay per second), in Curie (1Ci = 3.7*1010 decays per second = (3.7*1010bc)or in the case of very low activities in disintegrations per minute (dpm).

AMSAMS, Accelerator Mass Spectrometry, is mass spectrometry using an accelerator. At high energies,particles can be separated and counted that else would be indistinguishable. It is mainly used for themeasurement of long-lived cosmogenic radionuclides such as 14C or 10Be.

ArchaeometryThe application of scientific methods to archaeological problems.

AtlanticBesides the ocean, the term Atlantic denotes a climatic period at the end of the Holocene. It lastedfrom the 6th to the beginning of the 3rd millennium BC and was a period of warm and very moistclimate. Thermophilous species migrated north, and the Boreal mixed forest was replaced by the“climax forest”, containing trees like oak, lime and elm.

Background correctionA background correction in 14C dating is made by measuring a 14C-dead sample. A 14C ratio that ismeasured although the sample does not contain any 14C, is called background. The 14C ratios of othersamples have to be corrected for that backgroung 14C ratio.

BlubberThe fat of whales or other large marine animals.

BorealThe Boreal is the climatic period that precedes the Atlantic. It came after the cold period “YoungerDryas”, during which Europe was covered with Tundra and Taiga. Around 11,500 cal. BP the temper-ature rises quite sharply, which marks the beginning of the Boreal. The climate in that period varied,but it was mostly like today. Forests began covering the European plains, and a raising of the sea levelresulted in the formation of numerous islands. The Boreal ended around 8,000 cal. BC when the evenwarmer Atlantic began.

DaltonOne Dalton (Da) is one unified atomic mass unit (u), roughly equal to the mass of a proton orneutron. “In biochemistry and molecular biology literature (particularly in reference to proteins),the term ”dalton” is used, with the symbol Da. Because proteins are large molecules, they aretypically referred to in kilodaltons, or ”kDa”, with one kilodalton being equal to 1000 daltons”(http://en.wikipedia.org/wiki/Atomic mass unit on March 13, 2008).

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Decay constantThe decay constant λ of a radioactive substance is the inverse mean life, 1

τ . See also Half-life andMean life.

EmmerThe pristine form of wheat that was used in the Early Neolithic

EstuaryAn estuary is a body of water with one or more rivers flowing through it and with connection to theopen sea. It is often under tidal influence and the brackish water provides nutrients as a basis for richbiological activity.

Flake adzeGerman name “Scheibenbeil”. An adze that was produced by knapping flint flakes from a nucleus.

Flint knappingThe process of flintstone tool production

Funnel Beaker cultureThe Funnel Beaker culture is an early Neolithic culture that followed the Ertebølle culture. It stretchedacross the Netherlands, Northern Germany, Poland and Southern Scandinavia and lasted from c. 4200to c. 2800 BC.

GeestGeest or geestland denotes a landscape type in Northern Germany, Denmark and the Netherlands.It consists of sandy glacial deposits and is often next to marshland. It lies normally higher thanmarshlands and is slightly hilly.

Half-lifeThe half-life of a radioactive substance is the time after which half of the atoms are decayed. See alsoMean life.

High Atlantic Climatic OptimumThe High Atlantic Climatic Optimum is the “climax”, the warmest section, of the Atlantic.

HomeostaticBeing in a relatively stable state of equilibrium or having a tendency toward such a state between thedifferent but interdependent elements or groups of elements of an organism, population, or group (afterMerriam-Webster Online Dictionary, 28.01.2008).

Hunter-gatherersPeople whose subsistence is mainly based on hunted game and collected plants. Sometimes, fishing isalso included.

LA - Landesaufnahme (here: Archaologische Landesaufnahme)An “Archaologische Landesaufnahme” is an archaeological field survery where archaeological finds arecontinuously registered and mapped. In Schleswig-Holstein, the “Archaologische Landesaufnahme” isworking since about 80 years. From the Landesaufnahme, sites get individual numbers to identifythem, in combination with the name of the region or village next to which the site was found. Thetwo sites regarded in this thesis have thus the names “Schlamersdorf LA5” and “Kayhude LA8”.

Linear Pottery cultureThe abbreviation for this culture is LBK, after its German name “Linearbandkeramische Kultur”. Itis one of the oldest Neolithic farming cultures in Central Europe. It ranged from Western Hungary,Romania and the Ukraine over Western Slovakia, Poland and Germany up to Eastern France. It wasthus the biggest culture of the Neolithic, in terms of geographical spread.

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Mean lifeSymbol τ . Also mean lifetime. The mean life of a radioactive substance is the time after which1e = 1

2.718 of the atoms are decayed. See also Half-life and Decay constant.

MesolithicThe Mesolithic is the younger phase of the older (hunter-gatherer) stone age. It is the time since thelast ice age until the beginning of farming ((Mikkelsen 1978)). In regions outside Northern Europe thatwere not affected by the ice age, a division of the older stone age into Palaeolithic and Mesolithic isirrelevant. In Northern Europe, though, the landscape changed drastically as the ice age ended. Opengrass plains were herds of big mammals were grazing were replaced by dense forest which requireddifferent hunting strategies and so different tools, which is reflected in the archaeological record as atransition from one culture to another.

Michelsberg cultureThe Michelsberg culture (German: Michelsberger Kultur (MK)) is an important Neolithic culture inCentral Europe. Its conventional name is derived from the important excavated site on Michelsberg(or Michaelsberg) hill near Untergrombach, between Karlsruhe and Heidelberg (Baden-Wurttemberg).The Michelsberg culture is dated in the late 5th and the first half of the 4th millennium BC. Thus, itbelongs to the Central European Late Neolithic. Its distribution covered much of West Central Europe,along both sides of the Rhine

NeolithicThe younger stone age, where stone still was the most important raw material and metal, if known,only played a minor role. Agriculture and connected phenomena distinguish this phase from the olderstone age.

New ArchaeologyAlso processual archaeology. A movement beginning in the 1960’s that places emphasis on scientificmethods and defines culture as means of adaptation, thus describing a “cultural evolution”. The aim ofnew archaeology was to explore the people that made the artefacts found in archaeological excavations,the society they lived in and their way of life. The American archaeologist Lewis Binford was one ofits main advocats, why it sometimes is called “The new archaeology since Binford”. This movementcan be seen as a reaction to the culture history approach that dominated in that time. In culturehistory, emphasis lies on artefacts which are described and on the basis of which chronologies are builtup. The reconstruction of past human habits on the basis of artefacts is regarded infeasible in thecultural-historical approach.

Peltier coolerA Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfersheat from one side of the device to the other side against the temperature gradient (from cold tohot), with consumption of electrical energy. Thermoelectric junctions are generally only around 510%as efficient as the ideal refrigerator (Carnot cycle), compared with 4060% achieved by conventionalcompression cycle systems (reverse Rankine systems like a compressor). Due to the relatively lowefficiency, thermoelectric cooling is generally only used in environments where the solid state nature(no moving parts, maintenance-free) outweighs pure efficiency (http://en.wikipedia.org/w/index.php?-title=Thermoelectric cooling&oldid=186367236) on Jan 24, 2008).

PhloemPhloem is a transport tissue in plants. It transports mainly nutrients. The name is derived from theGreek word for bark, as the inner layer of a tree’s bark consists of phloem.

Phosphoenolpyruvate (PEP) carboxylasePEP carboxylase is an enzyme that catalyzes the addition of CO2 to phosphoenolpyruvate (PEP) toform the four-carbon compound oxaloacetate.

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Pot boilerPot boilers are stones which are heated in a fire and then used for heating liquids. This can be in aclay pot, a skin container or a cooking pit.

Provenance studiesIn provenance studies, chemical and other scientific methods are used for finding out, where an artefactor raw material comes from. The basis for these methods is the fact, that for example clay or flintdeposits have a characteristic chemical composition. When the chemical composition of a sample ismeasured, it can be compared to that of a range of possible raw material deposits.

Remote sensingRemote sensing is the gathering of information about an object without having physical contact tothat object. Examples are satellite pictures, radar or magnetic resonance imaging. These techniquescan for example be used for the detection of buried building structures.

Ribwort plantainLatin name Plantago lanceolata. A weed that is common on cultivated land and can therefore be usedas an indicator of agriculture or grazing. Originating from Europe, but now world-wide prevalent.

RoachA small fish of the Cyprinid family, between 25 and 45 cm long, that is common in many rivers andlakes throughout Europe

Rubisco enzymeRubisco, also written RuBisCO, is the abbreviation of Ribulose-1,5-bisphosphate carboxylase / oxy-genase. It is an enzyme that catalyzes the first major step of carbon fixation in the Calvin cycle ofphotosynthesis. It catalyzes either the carboxylation or oxygenation of ribulose-1,5-bisphosphate (alsoknown as RuBP) with carbon dioxide or oxygen. It is the most abundant protein in leaves and it maybe the most abundant protein on Earth (http://en.wikipedia.org/wiki/Rubisco on March 24, 2008).

Scanning electron microscope (SEM)An electron microscope in which a beam of focused electrons moves across the object with the secondaryelectrons produced by the object and the electrons scattered by the object being collected to form athree-dimensional image on a display screen (www.merriam-webster.com on March 7, 2008)

Shoe last axeAlso shoe last celt. A long and thin stone tool whose form reminds of a shoe maker’s last. They wereproduced by the early neolithic Linear Pottery culture which populated big parts of Europe. Shoe lastaxes were mainly used as wood working tools. In the Ertebølle culture, finds of shoe last axes indicatetrading connections to Neolithic cultures further south and the Linear Pottery culture.

SorrelLatin name Rumex acetosa. Sorrel is a perennial herb that is cultivated as a leaf vegetable(http://en.wikipedia.org/wiki/Sorrel on March 18, 2008).

Sub sample ID (SSID)The sub sample ID is used to identify different fractions and preparation steps of a sample in ourlaboratory.

Terminus ante quemLiterally Limit before which. A terminus ante quem describes a point in time before which a certainevent happened. Example: When a letter describes a certain event, the letter is a terminus ante quemfor the event, because the event happened before it was described in the letter.

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Terminus post quemLiterally Limit after which. A terminus post quem describes a point in time after which a certainevent happened. Example: When a coin is found in a grave, it is a terminus post quem for the burial,because the person was buried after the coin was produced.

TransgressionThe spread of the sea over land areas and the consequent unconformable deposit of sediments on olderrocks (www.merriam-webster.com on 07.03.2008)

XylemThe word xylem derives from the Greek word for wood. It is a transport tissue in plants and wood isthe most commonly known tissue of this type. It mainly transports water.

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List of Tables

1.1 Average δ15N values in bone collagen of different terrestrial and marine animals (Schoeningerand DeNiro 1984) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.1 Combustion and graphitisation of graphite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372.2 Combustion and graphitisation of Gel A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372.3 Single and double combustion and graphitisation of GelA . . . . . . . . . . . . . . . . . . . . 382.4 Graphitised samples for C/N measurements and SEM . . . . . . . . . . . . . . . . . . . . . . 442.5 Graphitisation yield of small samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442.6 Quartz tube combustion and graphitisation of GelA samples . . . . . . . . . . . . . . . . . . . 472.7 CO2 trapping tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4.1 Sherd samples from Kayhude and Schlamersdorf: sample type, NaOH concentration for pre-treatment and pretreatment yield. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

4.2 Quality of extracted “collagen”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824.3 Trave - modern samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844.4 Trave - reservoir ages of modern samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874.5 Trave - archaeological samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884.6 Alster - modern samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904.7 Alster - reservoir ages for modern samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904.8 Alster - archaeological samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914.9 C/N data of archaeological food crusts from Kayhude and modern food crusts . . . . . . . . . 93

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List of Figures

1.1 The radioactive decay of 14C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Bomb pulse in atmosphere and oceans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3 A tandem accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.4 Particle detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.5 AMS measurement procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.6 Fractionation of 13C and 14C during photosynthesis, respiration in soils, and dissolution by

groundwaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171.7 13C ranges in natural compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.1 Normal-sized graphitisation reaction tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342.2 The part of the graphitisation system with small reactors. . . . . . . . . . . . . . . . . . . . . 362.3 Graphitisation of two identically sized samples with cobalt and iron as catalyst. . . . . . . . . 392.4 Start of graphitisation with Co and Fe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402.5 Graphitisation of samples of different size with iron . . . . . . . . . . . . . . . . . . . . . . . . 402.6 Graphitisation of Water Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422.7 SEM pictures of graphitised samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432.8 Graphitisation of small samples in normal-sized (R11-R17) and small (R19 and R110) reactors 452.10 Small sample graphitisation on cobalt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452.9 Graphitisation of two small samples in small reactors on cobalt . . . . . . . . . . . . . . . . . 462.11 Graphitisation yield as a function of sample size for graphitisation on iron and cobalt . . . . 462.12 The continuous flow elemental analyzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492.13 Sample transfer for δ13C dual inlet (DI) measurements . . . . . . . . . . . . . . . . . . . . . . 512.14 Trapping CO2 from EA combustion for graphitisation . . . . . . . . . . . . . . . . . . . . . . 522.15 The valves that control the trapping process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532.16 Combustion and graphitisation of GelA - comparison between different graphitisation param-

eters after “traditionel” combustion in quartz tubes . . . . . . . . . . . . . . . . . . . . . . . . 54

3.1 Map of EBK sites with dated food crusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573.2 Map of Schlamersdorf and its surroundings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583.3 Map of Kayhude and its surroundings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593.4 Funnel beaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613.5 The reconstructed Ertebølle settlement

Photograph by Peter Marling/Scanpix Nordfoto . . . . . . . . . . . . . . . . . . . . . . . . . . 623.6 Rebuilding a pointed-base vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653.7 Copies of EBK pottery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

4.1 Water sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734.2 Photographs of the modern fish and shell samples. . . . . . . . . . . . . . . . . . . . . . . . . 754.3 Finishing a pointed-base vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764.4 Firing of the pointed-base vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774.5 Food crust production of fish and meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

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4.6 Bomb pulse extended with exponential decrease fit . . . . . . . . . . . . . . . . . . . . . . . . 864.7 Calibration of the archaeological samples from Schlamersdorf . . . . . . . . . . . . . . . . . . 894.8 Calibration of the archaeological samples from Kayhude . . . . . . . . . . . . . . . . . . . . . 924.9 The bomb pulse in the atmosphere and different parts of the oceans. . . . . . . . . . . . . . . 944.10 δ13C and δ15N values of food crusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

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Index

14C dating, 114N, 2415N, 24

Absolute international standard activity (AISA), 12Accelerator Mass Spectrometry, 6Alanine, 29Alster, 57, 60Ancylus Lake, 62Archaeological science, IArchaeometry, IAtlantic period, 60

Baltic Seaformation, 62

Blubber, 64Bomb pulse, 4

High precision radiocarbon dating, 4

Calibration (Radiocarbon), 5Calibration curve, 4Catalyst, 38Catastrophe theory, 69Cysteine, 29

Dating of pottery, 26Decay law, 2Dendrochronology, 6

Ellerbek culture, 62Ertebølle

culture, 61sedentariness, 63

potterylamp, 64pointed base vessel, 64

site, 61, 62economy, 63

Fractionation, 5Freshwater reservoir effect, 13Funnel Beaker culture, 61, 68

Garden of Eden argument, 66

Glutamic acid, 29Glycine, 29

Hardwater effect, 14High Atlantic climatic optimum, 62

Køkkenmøddinger, 61Kayhude, 56Kitchenmidden, 61Kitchenmiddens, 61

Late Mesolithic, 61Libby’s half-life, 4Litorina Sea, 62Litorina transgressions, 62

Marine reservoir effect, 13Marl, 60Mesolithic, 65Methionine, 29Michelsberg culture, 67, 68

Neolithic, 61, 65Neolithic revolution, 65Neolithisation, 65, 66Nordic Terminal Mesolithic, 61North Sea

formation, 62

Oxalic acid, 12

Pee Dee belemnite, 22Percent modern carbon, 12Photosynthesis

Calcin cycle (C3), 22Crassulacean acid metabolism (CAM), 23Hatch-Slack cycle (C4), 23

pmC, 12Pointed base vessel, 64Pot boiler, 57Proto-neolithic, 61

RadiocarbonDecay counting, 2

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half-life, 1Radiocarbon dating, 1Radiocarbon dating of pottery, 27Radiocarbon Revolution

Second Radiocarbon Revolution, 6Radiocarbon revolution, 1Reservoir effect, 13Run-off effect, 24

Schlamersdorf, 56Spitzboden (pointed base vessel), 64Suess effect, 4

Tandem Accelerator, 11Temper, 26Third radiocarbon revolution, 10Trave, 56, 60, 62Typological sequence, 26

U-technique (pottery), 65USGS Radiocarbon Dating Laboratory, 4

Water hardness, 14, 60Water Samples

Graphitisation, 41Wiggles, 4

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Declaration:I hereby declare that I wrote this thesis independently and that I did not use any sources and auxiliary

means other than the ones indicated.

Erklarung:Ich versichere, daß ich diese Arbeit selbstandig verfasst und keine anderen als die angegebenen Quellen

und Hilfsmittel benutzt habe.

Heidelberg, March 31, 2008.............................................

Bente Philippsen

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