Holocene environmental changesand climate variability in theEastern Mediterranean Multiproxy sediment records from the Peloponnese peninsula, SW Greece

 Christos Katrantsiotis

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Dissertations in Physical Geography No. 2

Doctoral Thesis in Physical Geography at Stockholm University, Sweden 2019

Department of Physical Geography

ISBN  978-91-7797-664-6ISSN 2003-2358

Christos Katrantsiotisholds BSc in Geology and MSc in ClimateScience and Quaternary Geology. His maininterest is the reconstruction ofpaleoenvironmental and paleoclimaticchanges using diatoms and biomarker lipids insediment cores. His current research focuseson the Mediterranean region and NorthernScandinavia. He also has special interest indiatom morphology and taxonomy.

This thesis aims to contribute to a better understanding of climateevolution and the related drivers in the central-eastern Mediterraneanover the last 6000 years, a period of centennial-millennial climatechanges whose nature is not well-understood. The study area is thePeloponnese peninsula, SW Greece, characterized by high climaticheterogeneity, broad spectrum of natural archives and richarchaeological history. The identification of climate signal in fossilrecords, however, might be complicated in this region due to theinteraction of various environmental factors. The development of adenser network of multiproxy records can help to optimize theinterpretative accuracy and identify synchronous changes attributed toa common climate mechanism. Here, a multiproxy approach mainlybased on diatom and biomarker analyses is applied on radiocarbon-dated sediment cores from the Agios Floros fen and the GialovaLagoon in SW Peloponnese and the Ancient Lake Lerna in NEPeloponnese. The results highlight the interaction between climate,tectonics and human activities and reveal variations in theprecipitation/temperature gradient over the Peloponnese, attributed tothe interplay between different atmospheric circulation patterns. Thisinterplay can further be elucidated by integrating the growing networkof proxy records with paleoclimate modelling, which is also crucial toimprove climate forecasting capabilities.

Holocene environmental changes and climatevariability in the Eastern MediterraneanMultiproxy sediment records from the Peloponnese peninsula, SWGreeceChristos Katrantsiotis

Academic dissertation for the Degree of Doctor of Philosophy in Physical Geography atStockholm University to be publicly defended on Friday 14 June 2019 at 13.00 in De Geersalen,Geovetenskapens hus, Svante Arrhenius väg 14.

AbstractThis thesis presents multiproxy reconstructions of the mid to late Holocene climate and environmental changesin the Peloponnese peninsula, SW Greece. The combined dataset consists of diatom, biomarker and X-rayfluorescence spectrometry (XRF) elemental data in radiocarbon-dated sediment cores taken from the Agios Floros fen andthe Gialova Lagoon in SW Peloponnese and the Ancient Lake Lerna in NE Peloponnese. Overall, the results highlightthe complex interaction between climate, tectonics and human activities in the landscape development and further revealchanges in the W-E precipitation/temperature gradient over the peninsula connected to shifts in the large-scale atmosphericcirculation patterns.

The Agios Floros study provides a 6000-year hydrological record based on diatoms and hydrogen isotopic (δD) analysisof aquatic plant-derived n-C23 alkanes. The records indicate two decadal-long periods of deep water conditions at ca 5700and 5300 cal BP, largely attributed to local tectonic processes and the hydrological anomalies of the nearby karst springs.A period of intermediate water level at ca 4600 cal BP is dominated by the new fossil species Cyclotella paradistinguendadescribed in this thesis. The gradual development of a fen at ca 4500 cal BP is attributed to a combination of humanactivities and drier conditions, the latter culminating in SW Peloponnese mainly after ca 4100 cal BP. From ca 2800 calBP and onwards, there is evidence for flooding events probably related to marked rainfall seasonality.

The n-alkane δD profiles and XRF data analyzed in the Gialova core co-vary with each other indicating a commonclimate signal during the last 3600 years, which resembles the Agios Floros record. The n-alkane δ13C values show highcontribution of aquatic vegetation to sedimentary organic matter during wet/cold periods. The n-alkane δD signals fromthe Lake Lerna also exhibit a similar pattern to each other providing further evidence for precipitation/temperature changesover the last 5000 years.

Comparison of the δD records reveals sometimes similar and sometimes opposing signals between NE and SWPeloponnese, which can be attributed to the relative dominance of high latitude and low latitude atmospheric patterns overthe peninsula. The records show wet conditions at ca 5000-4600 cal BP likely associated with the weakening of the Hadleycirculation. High humidity is also evident at ca 4500-4100, ca 3000-2600 (more unstable in SW) and after ca 700 cal BPwith drier conditions at ca 4100-3900 and ca 1000-700 cal BP. These periods correspond to regional climate changes, whenthe North Atlantic Oscillation (NAO) likely exerted the main control with NAO (+) creating conditions of reduced moisture.A NE-SW climate see-saw with drier conditions in NE Peloponnese is evident at ca 4600-4500, ca 3200, ca 2600-1800 andca 1200-1000 cal BP and a reversal at ca 3900-3300 ca 3200-3000 and ca 1800-1300 cal BP. The dipole pattern is likelydriven by shifts in the North Sea–Caspian Atmospheric pattern (NCP), with NCP (+) leading to wetter and colder conditionsin NE Peloponnese. The opposing signal can also be explained by changes in summer temperatures driven by the Asianmonsoon intensity. Strong monsoonal periods coincide with cool summers in Lerna, due to the northerly winds (Etesians),in contrast to SW Peloponnese, located on the lee side of the mountain and most affected by the large-scale air subsidence.

Keywords: Mediterranean, Greece, Peloponnese, Holocene, sediments, diatoms, n-alkanes, stable isotopes, tectonics,climate variability, monsoons, NAO, NCP.

Stockholm 2019http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-167747

ISBN 978-91-7797-664-6ISBN 978-91-7797-665-3ISSN 2003-2358

Department of Physical Geography

Stockholm University, 106 91 Stockholm

HOLOCENE ENVIRONMENTAL CHANGES AND CLIMATE VARIABILITY IN THEEASTERN MEDITERRANEAN 

Christos Katrantsiotis

Holocene environmental changes andclimate variability in the EasternMediterranean 

Multiproxy sediment records from the Peloponnese peninsula, SW Greece 

Christos Katrantsiotis

©Christos Katrantsiotis, Stockholm University 2019 ISBN print  978-91-7797-664-6ISBN PDF 978-91-7797-665-3ISSN 2003-2358 Paper I © The Holocene, SAGE PublicationsPaper II © Diatom Research, Taylor & Francis OnlinePaper III © Journal of Quaternary Science, John Wiley & Sons, Inc.Paper IV © Quaternary Science Reviews, Elsevier B.V.Paper V © Global and Planetary Change, Elsevier B.V. Cover illustration: Gialova Lagoon. Photo by Christos Katrantsiotis, 2016Printed in Sweden by Universitetsservice US-AB, Stockholm 2019Distributor: Department of Physical Geography, Stockholm University

Abstract

This thesis presents multiproxy reconstructions of the mid to late Holocene climate and environmental

changes in the Peloponnese peninsula, SW Greece. The combined dataset consists of diatom, biomarker

and X-ray fluorescence spectrometry (XRF) elemental data in radiocarbon-dated sediment cores taken

from the Agios Floros fen and the Gialova Lagoon in SW Peloponnese and the Ancient Lake Lerna in NE

Peloponnese. Overall, the results highlight the complex interaction between climate, tectonics and human

activities in the landscape development and further reveal changes in the W-E precipitation/temperature

gradient over the peninsula connected to shifts in the large-scale atmospheric circulation patterns.

The Agios Floros study provides a 6000-year hydrological record based on diatoms and hydrogen

isotopic (δD) analysis of aquatic plant‐derived n‐C23 alkanes. The records indicate two decadal-long

periods of deep water conditions at ca 5700 and 5300 cal BP, largely attributed to local tectonic processes

and the hydrological anomalies of the nearby karst springs. A period of intermediate water level at ca

4600 cal BP is dominated by the new fossil species Cyclotella paradistinguenda described in this thesis.

The gradual development of a fen at ca 4500 cal BP is attributed to a combination of human activities and

drier conditions, which culminate in SW Peloponnese mainly after ca 4100 cal BP. From ca 2800 cal BP

and onwards, there is evidence for flooding events probably related to marked rainfall seasonality.

The n-alkane δD profiles and XRF data analyzed in the Gialova core co-vary with each other

indicating a common climate signal during the last 3600 years, which resembles the Agios Floros record.

The n-alkane δ13C values show high contribution of aquatic vegetation to sedimentary organic matter

during wet/cold periods. The n-alkane δD signals from the Lake Lerna also exhibit a similar pattern to

each other providing further evidence for precipitation/temperature changes over the last 5000 years.

Comparison of δD records reveals sometimes similar and sometimes opposing signals between NE

and SW Peloponnese, which can be attributed to the relative dominance of high-latitude and low-latitude

atmospheric patterns over the peninsula. The records show wet conditions at ca 5000-4600 cal BP likely

associated with the weakening of the Hadley circulation. High humidity is also evident at ca 4500-4100,

ca 3000-2600 (more unstable in SW) and after ca 700 cal BP with drier conditions at ca 4100-3900 and ca

1000-700 cal BP. These periods correspond to regional climate changes, during which the North Atlantic

Oscillation (NAO) likely exerted the main control with NAO (+) creating conditions of reduced moisture.

A NE-SW climate see-saw with drier conditions in NE Peloponnese is evident at ca 4600-4500, ca 3200,

ca 2600-1800 and ca 1200-1000 cal BP and a reversal at ca 3900-3300 ca 3200-3000 and ca 1800-1300

cal BP. The dipole pattern is likely driven by shifts in the North Sea–Caspian Atmospheric pattern (NCP),

with NCP (+) leading to wetter and colder conditions in NE Peloponnese. The opposing signal can also be

explained by changes in summer temperatures driven by the Asian monsoon intensity. Strong monsoonal

periods coincide with cool summers in Lerna, due to the northerly winds (the Etesians), in contrast to SW

Peloponnese, located on the lee side of the mountain and most affected by the large-scale air subsidence.

Sammanfattning

Denna avhandling presenterar s.k. multiproxyrekonstruktioner av klimatvariationer under mitt- och sen-

holocen på Peloponnesos-halvön, sydvästra Grekland. Rekonstruktionerna baseras på diatoméer,

biomarkörer och XRF-data i kol14-daterade sedimentkärnor från Agios Floros-kärret och Gialova-

lagunen på sydvästra Peloponnesos och den nu igenvuxna Lerna-sjön på nordöstra Peloponnesos.

Resultaten belyser samspelet mellan klimat, tektonik och mänskliga aktiviteter i landskapsutvecklingen

och påvisar dessutom förändringar i den väst-östliga nederbörds/temperaturgradienten över halvön i

samband med förändringar i storskaliga atmosfärsmönster.

Agios Floros-studien omfattar de senaste ca 6000 åren och med hjälp av diatoméanalys har

paleohydrologiska förändringar rekonstruerats. Rekonstruktionen stöds av analyser av deuterium (δD)

och n-C23-alkaner från akvatiska växter. Båda analysmetoderna anger två decennielånga perioder med

djupa vattenförhållanden vid ca 5700 och 5300 kal BP, vilket huvudsakligen kan förklaras med tektoniska

processer och hydrologiska anomalier i närliggande karstkällor. En period med intermediära vattennivåer

vid ca 4600 kal BP domineras av en ny fossil diatoméart, Cyclotella paradistinguenda som beskrivs för

första gången i denna avhandling. Agios Floros började utvecklas till ett kärr ca 4500 kal BP på grund av

en kombination av mänskliga aktiviteter och de torrare förhållanden som rådde på sydvästra

Peloponnesos, huvudsakligen efter ca 4100 kal BP. Med början ca 2800 kal BP finns det bevis för

översvämningshändelser som sannolikt är förknippade med mer markerade säsongsvariationer i

nederbörden.

δD-analyser av n-alkaner och XRF-data som analyserats i kärnan från Gialova-lagunen samvarierar

med varandra, vilket indikerar en gemensam klimatsignal under de senaste 3600 åren, liknande den som

data från Agios Floros visar. n-Alkan-värden från δ13C från Gialova-kärnan visar högt inslag av

vattenlevande vegetation i det organiska materialet under våta och kalla tidsperioder. δD-variationer i n-

alkanerna från Lake Lerna visar ett nästan identiskt mönster som ger ytterligare bevis för nederbörds- och

temperaturförändringar under de senaste 5000 åren.

Jämförelser av variationer i δD visar ibland motsatta och ibland liknande signaler mellan nordöstra

och sydvästra Peloponnesos, vilket kan förklaras med den relativa dominansen mellan atmosfäriska

mönster på hög latitud eller låg latitud över halvön. δD-analyser visar fuktiga förhållanden vid ca 5000-

4600 kal BP som troligen är förknippade med försvagningen av Hadley-cirkulationen. Blötare

förhållanden är också uppenbar vid ca 4500-4100, ca 3000-2600 (mer instabil i sydväst) och efter ca 700

kal BP med torrare perioder vid ca 4100-3900 och ca 1000-700 kal BP. Under dessa perioder med

regionala klimatförändringar var den nordatlantiska oscillationen (NAO) dominerande och en positiv

NAO skapade förhållanden med reducerad fuktighet. Ett nordostligt-sydvästligt motsatsförhållande med

torra förhållanden på nordöstra Peloponnesos påvisas vid ca 4600-4500, ca 3200, ca 2600-1800 och ca

1200-1000 kal BP med en omkastning vid ca 3900-3300 ca 3200-3000 and ca 1800-1300 cal BP.

Dipolmönstret drivs sannolikt av förändringar i det s.k. Nordsjö-Kaspiska atmosfäriska mönstret (NCP),

där ett positivt NCP-index leder till fuktigare och kallare förhållanden på nordöstra Peloponnesos. Den

motsatta signalen kan även förklaras av de sommartemperaturförändringar som drivs av den asiatiska

monsunintensiteten. Starka monsunperioder sammanfaller med svala somrar i Lerna, på grund av de

nordliga s.k. etesiska vindarna, i motsats till sydvästra Peloponnesos, som är beläget på läsidan av bergen

och är mer påverkad av sjunkande luftmassor.

List of papers

This doctoral thesis consists of this summary and the following five papers, which are referred to by their

Roman numerals in the text.

I. Katrantsiotis, C., Norström, E., Holmgren, K., Risberg, J., Skelton, A., 2015. High-resolution

environmental reconstruction in SW Peloponnese Greece covering c. the last 6000 years:

Evidence from Agios-Floros fen. The Holocene 26, 188–204.

https://doi.org/10.1177/0959683615596838

II. Katrantsiotis, C., Risberg, J., Norström, E., Holmgren, K., 2016. Morphological study of

Cyclotella distinguenda and a description of a new fossil species Cyclotella paradistinguenda sp.

nov. from the Agios Floros fen, SW Peloponnese, Greece in relation to other Cyclotella species.

Diatom Research 31, 243–267. https://doi.org/10.1080/0269249X.2016.1211178

III. Norström, E., Katrantsiotis, C, Finné, M., Risberg, J., Smittenberg, R., Bjursäter, S., 2018.

Biomarker hydrogen isotope composition (δD) as proxy for Holocene hydro-climatic change and

seismic activity in SW Peloponnese, Greece. Journal of Quaternary Science 33, 563–574.

https://doi.org/10.1002/jqs.3036

IV. Katrantsiotis, C., Kylander, M., Smittenberg, R., Yamoah, K.K.A., Hättestrand, M., Avramidis,

P., Strandberg, N.A., Norström, E., 2018. Eastern Mediterranean hydroclimate reconstruction

over the last 3600 years based on sedimentary n-alkanes, their carbon and hydrogen isotope

composition and XRF data from the Gialova Lagoon, SW Greece. Quaternary Science Reviews

194, 77–93. https://doi.org/10.1016/j.quascirev.2018.07.008

V. Katrantsiotis, C., Norström, E., Smittenberg, R., Finné, M., Weiberg, E., Hättestrand, M.,

Avramidis, P., Wastegård S., 2019. Climate changes in the Eastern Mediterranean over the last

5000 years and their links to the high-latitude atmospheric patterns and Asian monsoons. Global

and Planetary Change 175, 36–51. https://doi.org/10.1016/j.gloplacha.2019.02.001

Author contributions

The following people have contributed to this thesis: Elin Norström (EN), Karin Holmgren (KH), Stefan

Wastegård (SW), Jan Risberg (JR), Rienk Smittenberg (RS), Alasdair Skelton (AS), Malin Kylander

(MK), Martina Hättestrand (MH), Pavlos Avramidis (PA), Kweku Yamoah (KY), Martin Finné (MF),

Erika Weiberg (EW), Nichola Strandberg (NS), and Stefan Bjursäter (SB). All co-authors are

acknowledged for reading and commenting on the manuscripts.

I. Conceived and designed by CK. CK and EN led the field work planning and performance. CK

described and subsampled the Agios Floros sediment core at the Peloponnese University,

Greece. CK performed the diatom analysis (sample preparation, diatom identification and

counting), produced the age-depth model, prepared the figures, made the interpretation and

wrote the paper. CK and EN prepared samples for bulk geochemical analysis. MK contributed

with XRF analysis of subsamples. AS helped out with the tectonic interpretation.

II. Conceived and designed by CK. CK carried out the light and scanning electron microscopic

analysis, prepared the figures, described the new diatom species, made the interpretation and

wrote the paper.

III. Conceived and designed by EN. CK and EN led the field work planning and performance. CK

described and subsampled the Agios Floros sediment core at the Peloponnese University,

Greece. EN performed the n-alkane extraction and quantification as well as carried out the

compound-specific isotope analysis of n-alkanes. EN prepared the figures, made the

interpretation and wrote the paper. CK wrote the introduction and the regional settings as well as

contributed to the interpretation. SB prepared the topographical map of the Messenian plain.

IV. Conceived and designed by CK. CK and EN led the field work planning and performance. CK

described and subsampled the Gialova sediment core at the Peloponnese University, Greece. CK

performed the n-alkane extraction and quantification and compound-specific isotope analysis of

n-alkanes, prepared and ran samples for XRF analysis with the assistance of MK, produced the

age-depth model, prepared the figures, made the interpretation and wrote the paper. MK

contributed with the XRF interpretation.

V. Conceived and designed by CK. CK, EN and MH led the field work planning and performance.

CK and MH described and subsampled the Lerna sediment core at Stockholm University. CK,

with the assistance of RS, performed the n-alkane extraction and quantification. CK carried out

the compound-specific isotope analysis of n-alkanes, construction of the age-depth model,

prepared the figures, made the interpretation and wrote the paper.

Table of Contents

1. Introduction.......................................................................................................................... 1 2. Thesis objectives ................................................................................................................ 2 3. Eastern Mediterranean climate .......................................................................................... 2

3.1. Winter atmospheric circulation patterns ................................................................ 3 3.2. Summer atmospheric circulation patterns ............................................................. 3

4. The Peloponnese ................................................................................................................. 4 4.1. Topography and climate ........................................................................................ 4 4.2. Geology and lanscape development. .................................................................... 4 4.3. Human occupation. ............................................................................................... 5

5. Description of sites ............................................................................................................. 5 5.1. Messenian plain/Agios Floros Fen ........................................................................ 5 5.2. Gialova Lagoon ..................................................................................................... 6 5.3. Lake Lerna ............................................................................................................ 7

6. Material and methods ........................................................................................................ 8 6.1. Field work. ............................................................................................................. 8 6.2. Proxy description and laboratory work .................................................................. 8

6.2.1. Radiocarbon dating ................................................................................ 8 6.2.2. Siliceous microfossils ............................................................................. 9 6.2.3. Organic geochemistry .......................................................................... 10 6.2.4. XRF core scanning ............................................................................... 15

7. Results ................................................................................................................................ 16 7.1. Paper I ................................................................................................................. 16 7.2. Paper II ................................................................................................................ 18 7.3. Paper III ............................................................................................................... 19 7.4. Paper IV............................................................................................................... 20 7.5. Paper V................................................................................................................ 21

8. Discussion ......................................................................................................................... 22 8.1. Chronology and resolution .................................................................................. 22 8.2. Proxy data ........................................................................................................... 23

8.2.1. Diatom preservation ............................................................................. 23 8.2.2. The new diatom species and its affinity ............................................... 24 8.2.3. Origins of n-alkanes. ............................................................................ 25 8.2.4. Factors behind δD variability ................................................................ 26

8.3. The role of tectonics in abrupt hydrological changes in the Agios Floros fen ..... 27 9. Regional climate reconstruction ..................................................................................... 29 10. Drivers of Holocene climate variability ......................................................................... 33

10.1. High-latitude atmospheric patterns ................................................................... 33 10.1.1. Physical mechanism ........................................................................... 33

10.2. Effects of African and Asian monsoons ............................................................ 35 11. Conclusions ..................................................................................................................... 36 12. Future perspectives ........................................................................................................ 37 13. Financial support ............................................................................................................ 38 14. Acknowledgements ......................................................................................................... 38 15. References ....................................................................................................................... 39

Abbreviations

ACL Average chain length

AMS Accelerator mass spectrometry

C/N Carbon/Nitrogen ratio

cal BP Calibrated years before present (BP = 1950)

CONISS Constrained incremental sum-of-squares

CPI Carbon preference index

EA/WR East Atlantic/West Russia

GC-MC Gas chromatography-mass spectrometry

GC-IRMS Gas chromatograph-isotope ratio mass spectrometer

IPCC Intergovernmental panel on climate change

IRD Ice rafted debris

ITCZ Intertropical Convergence Zone

LIA Little Ice Age

LM Light microscope

m a.s.l. Meters above sea level

MCA Medieval Climate Anomaly

MO Mediterranean Oscillation

NAO North Atlantic Oscillation

NCP North Sea-Caspian Pattern

OM Organic matter

OSL Optically stimulated luminescence

PCA Principal component analysis

SEM Scanning electron microscope

TN Total nitrogen

TOC Total organic carbon

VPDB Vienna Pee Dee Belemnite

VSMOW Vienna Standard Mean Ocean Water

XRF X-ray fluorescence

δ13C Stable carbon isotope

δD Stable hydrogen isotope

δ18O Stable oxygen isotope

1

1. Introduction

The global climate has been experiencing significant

warming during the last decades which has primarily

been attributed to anthropogenic greenhouse forcing

(IPCC, 2014). This climate change is spatially and

temporally non-uniform and affects some regions more

than others, with variable shifts in temperatures and

precipitation patterns (Ji et al., 2014). There is an

ongoing debate on whether an increasing risk of

droughts exists worldwide, or whether wet areas are

getting wetter and the arid regions drier under global

warming (Dore, 2005; Feng and Zhang, 2015).

Natural climate variability operates in a similar way

on all timescales (different impacts on different areas)

and is superimposed on human-induced climate change.

This complicates the accurate detection and attribution

of human influence on climate. More knowledge of past

climatic fluctuation is required to understand the nature

and rate of the current climate change, to distinguish

anthropogenic effects, and to accurately project climate

system response to future changes (Jansen et al., 2007).

Instrumental records span only the last centuries, a

period too short to understand the natural climatic

variability. Natural archives such as lake sediments,

stalagmites, ice-cores and tree rings offer the

opportunity to extend this knowledge over longer,

geological timescales. These archives contain a variety

of proxies related to different climate variables and can

preserve information about these variables at different

time-scales. Thus, paleoenvironmental studies have

been characterized as the ultimate source of our

understanding of the nature and rate of past climatic

variability and anthropogenic effects (Bradley, 2014).

The Mediterranean region is particularly sensitive

to climate changes due to its semi-arid conditions, its

intermediate position between the mid-latitude and

subtropical atmospheric systems and its high climatic

heterogeneity characterized by altitude gradients,

microclimates and extreme seasonality (Lionello et al.,

2006; Ulbrich et al., 2012). In addition, physico-

geographical parameters such as orography, land-sea

interaction and the Mediterranean Sea, a source of

moisture and a heat reservoir, make the regional

response to large-scale climate forcing rather complex

(Lionello et al., 2006; Giorgi and Lionello, 2008). The

Intergovernmental Panel for Climate Change (IPCC)

has identified the Mediterranean as a climatic hot spot

where most countries are already experiencing a high

frequency of droughts, water scarcity, forest fires and

increasing desertification (IPCC, 2014; Loizidou et al.,

2016). These conditions are predicted to be exacerbated

leading to dire consequences for ecosystems and human

societies (IPCC, 2014; Guiot and Cramer, 2016).

The pronounced sensitivity of the Mediterranean

region to climate changes has driven intense research

on both the study of future and past climates. Special

focus has been placed on the Holocene, a period which

involves possible human response to climate change

(Kaniewski et al., 2013; Knapp and Manning, 2016).

The Holocene is generally characterized by centennial-

millennial changes whose nature and chronological

boundaries are not well-defined. A large body of dataset

from the Mediterranean region provides evidence of

complex spatial and temporal climatic variability with

clear patterns from east to west and from north to south

during the Holocene (e.g. Dormoy et al., 2009; Finné et

al., 2011; Roberts et al., 2012; Magny et al., 2013;

Peyron et al., 2013). In addition to this climatic

heterogeneity, limitations in dating accuracy hamper

regional comparisons and discussions regarding the

causes and the effects. All these factors highlight the

need to improve both the spatial coverage and quality of

the existing data sets. The establishment of a denser

network of proxy records around the Mediterranean can

contribute to our understanding of regional climatic

differences within the basin and its underlying

mechanisms as well as the relationship between the

climate, the physical environment and human actions.

The Peloponnese peninsula in SW Greece at the

most south-eastern point of Europe offers the

opportunity to explore the presence of such regional

climatic differences and/or common patterns. The

peninsula is characterized by a west-east rainfall/

temperature gradient attributed to its topography and

the influence of different atmospheric circulation

patterns from the mid-latitude and the low-latitude

regions. Therefore, comparison of climate records from

the western and eastern parts of the peninsula can reveal

shifts in the large-scale teleconnections that affect the

Mediterranean region. In addition, the Peloponnese

peninsula offers a broad spectrum of natural archives

(e.g. speleothems, lake sediments) allowing climate

reconstructions with high temporal and spatial

resolution. The peninsula is also rich in archaeological

findings with numerous well-preserved and precisely

dated archaeological sites and is thus highly interesting

for studies on how climate changes have impacted

different societies in the past (Weiberg et al., 2016).

Palaeoenvironmental studies in the Peloponnese

have a long tradition from a variety of disciplines with

special attention on the relationship between climate,

landscape changes and past settlements. These studies

have been based on biological (pollen, foraminifera)

and geochemical records from lagoons and lakes (Kraft

et al., 1980; Jahns, 1993; Papazisimou et al., 2005;

Cundy et al., 2006; Lazarova et al., 2012; Heymann et

al., 2013; Unkel et al., 2014). However, limitations

related to dating accuracy and proxy preservation have

often hampered the interpretations. Oxygen isotopes

(δ18Ο) in speleothems have recently been applied in

paleoclimate studies from the Peloponnese (Boyd,

2015; Finné et al., 2014, 2017). Although speleothem

records are of high quality and resolution, they often

cover limited periods and do show occasional hiatuses.

Despite the abundance of paleoclimatic data, proxy

interpretations in the Peloponnese are complicated by

the interaction of various environmental factors, i.e.

tectonics, sea level changes and human activities in the

landscape development. These factors might cause

2

similar variations in the proxy records, which can

impede the unambiguous separation of climate from

non-climatic signals. In this case, a multiproxy

approach derived from independent sources will

potentially help to discriminate between different

environmental factors, and particularly to identify

synchronous changes in proxy records attributed to a

common climate mechanism. In addition to this, the

comparison of records from different sites of the

Peloponnese can enable the separation of local

environmental changes from regional climate signals.

In this thesis, a multi-proxy approach is applied on

three radio-carbon dated sediment cores retrieved from

three climatic sensitive ecosystems in SW and NE

Peloponnese. The locations of sites on SW-NE transect

aims to establish a small network of paleoclimatic data

from different climatic zones of the Peloponnese

peninsula. This can further enable us to stress local

climate differences and provide a more accurate

assessment of the regional climate variability and its

connection to the large scale atmospheric patterns.

The cores were analyzed for different biological and

geochemical proxies: diatoms, the distribution and

compound specific carbon (13C) and hydrogen (D)

isotope compositions of leaf-wax n-alkanes, bulk

geochemistry and X-ray fluorescence spectrometry

(XRF) elemental data. Diatoms are single-cell algae

that exhibit high diversity and well-defined ecological

preferences. Diatom studies are rare in Greece (Wilson

et al., 2008; Jones et al., 2013) while elsewhere this

method have successfully been used for paleo-

environmental reconstructions (e.g. Gasse, 1987,1994;

Hassan, 2013; Cvetkoska et al., 2014). Organic geo-

chemical proxies, so-called biomarkers, are preserved

in sediments over thousands of years, and along with

their isotopic signal, they are useful markers for past

hydroclimatic conditions given their clear biological

origin (Peters et al., 2005). In Greece, this approach has

been applied on marine sediments (e.g. Triantaphyllou

et al., 2009; Gogou et al., 2016) and terrestrial material

combined with compound specific isotope analysis

(Schemmel et al., 2016; Norström et al., 2017). The

XRF method is increasingly being used in stratigraphic

studies to investigate changes in elemental composition,

attributed to various environmental processes in lake

ecosystems and catchments (Croudace et al., 2006).

The continuous multiproxy records of climatic

variability in the Peloponnese presented in this thesis

will fill important gaps in the existing hydroclimate

studies from the central-eastern Mediterranean region.

The growing network of paleoclimate research will

further contribute to a more accurate understanding of

the natural climate processes, so that current climate

change can be placed better in a historical context. Such

an approach will further allow testing the performance

of climate models. If a model can correctly predict

trends in the past, one may expect it to predict future

trends accurately as well. This is vital to responsibly

inform policy makers and citizens about the potential

future climate changes in this drought-prone region.

2. Thesis objectives

The overall objectives of the work presented in this

PhD thesis are 1) to increase the spatial coverage of

Holocene paleoclimate data from the Peloponnese and

also 2) to improve the understanding of the Holocene

climate changes in the central-eastern Mediterranean.

The specific objectives of this PhD thesis are to: establish continuous paleoclimatic records from SW

and NE Peloponnese based on diatom and

geochemical analyses of three sediment cores: two

records from SW Peloponnese covering the last

6000 and 3600 years, respectively and one record

from NE Peloponnese spanning the last 5000 years.

discriminate between various environmental factors

which influence the multiproxy records, and

specifically to discern climate-induced changes.

identify short-term events by establishing high

resolution records, and to understand the nature of

those events and their relation to tectonic activities.

evaluate the applicability of n-alkane δD data as a

paleoclimate proxy in this particular environmental

setting by means of comparing the δD records with

other independent proxies and regional records.

trace the sources of sedimentary organic matter

(OM) in the studied sites, which can further aid with

more accurate interpretation of n-alkane δD data.

examine diatom morphology by means of light and

scanning electron microscope (LM and SEM).

present the first comprehensive list of fossil diatoms

observed in Greece and also to contribute to the

Mediterranean database of diatom paleotaxa.

The goals related to paleoclimate investigation are to: reconstruct shifts in the W-E rainfall gradient over

the Peloponnese by comparing the δD signals with

each other and with other Peloponnesian records.

produce a wider climate reconstruction for the

eastern Mediterranean region by comparing the

Peloponnesian records with other regional studies.

understand the driving mechanisms behind the

observed climate changes, and particularly to

assess linkages with the high latitude atmospheric

patterns and the African/Asian monsoons.

3. Eastern Mediterranean climate

The Mediterranean climate is characterized by large

seasonal variations with hot and dry summers and mild

/cold and wet winters. This variation is a result of the

interaction between the Subtrophic High and the mid-

latitude westerlies leading to a distinct sensitivity of the

local climate to the variability of supraregional

atmospheric patterns. In addition, the Mediterranean

climatic conditions are influenced by the complexity of

the terrain as well as the interaction between land-sea,

and the Mediterranean Sea itself (Lionello et al., 2006).

3

Winter climatic conditions in

the Eastern Mediterranean

are mainly dominated by the

interplay between the mid-

and high-latitude atmospheric

patterns. This includes

variations in the location,

strength and spatial extension

of the Azores High, the

Icelandic Low and also the

Siberia High (Fig. 1) (Trigo

et al., 2006; Küttel et al.,

2011). The precipitation

regime is largely associated

with moisture rich air carried

by the low pressure systems

originating from the North

Atlantic region and the western Mediterranean (Ulbrich

et al., 2012). The path of these systems is influenced by

the North Atlantic Oscillation (NAO) modes defined as

the normalized pressure difference between Iceland (the

Icelandic Low) and the Azores Portugal (the Azores

High). Positive (negative) NAO creates drier (wetter)

conditions as less air from the North Atlantic penetrates

into the region (Brandimarte et al., 2011). The

Mediterranean region also favors the development of

cyclones with synoptic to mesoscale characteristics

(Lionello et al., 2016). Cyclones are produced as a

result of the advection of polar air masses over the

warm sea as well as the passage of North Atlantic

synoptic systems and their interaction with topography

(Trigo et al., 2002). Cyclogenesis takes place within the

Mediterranean region in preferable places such as Gulf

of Genova, Ionian Sea, Aegean Sea and Cyprus from

which cyclones track SE-ward (Alpert et al., 1990).

Conditions for northerly flows of cold and dry air

masses over the Mediterranean are mainly associated

with a westward ridging of the Siberian High and also

the pressure difference between the western and eastern

parts of the basin (Maheras et al., 1999). In particular,

Mediterranean Oscillation (MO) is defined by the

pressure differences between stations at Algiers and

Cairo and is linked to NAO modes (Fig. 1) (Conte et

al., 1989). Positive (negative) MO modes are dominated

by an anticyclone (cyclone) in the Western

Mediterranean and low (high) pressure systems in the

Eastern Mediterranean leading to a southward

(northward) flow of cool (warm) and dry (wet) air over

the Eastern Mediterranean (Feidas et al., 2007). In

addition, the winter temperature and precipitation are

influenced by the pressure difference between the North

Sea and the Caspian Sea, the so-called North Sea-

Caspian Pattern (NCP) (Kutiel et al., 2002). An

anticyclonic (cyclonic) upper circulation anomaly in the

North Sea and an cyclonic (anticyclonic) circulation

pattern north of the Caspian Sea induce a southward

cold (northward warm) air stream over Balkans and

Turkey resulting in lower (higher) temperatures (Feidas,

2017). During positive (negative) NCP phases, the areas

exposed to northern (southern) maritime trajectories,

such as the eastern continental Greece and the Black

Sea region (western Greece and southern Turkey),

receive higher precipitation than during negative

(positive) NCP phases (Kutiel and Benaroch, 2002).

3.2. Summer atmospheric circulation patterns

Summer conditions in the eastern Mediterranean region

are dominated by two processes. The first process is the

dynamic subsidence, which inhibits cloud formation

and convection, resulting in a prolonged warm and dry

summers (Dayan et al., 2017). This has traditionally

been associated with the African monsoons and the

subtropical descending branch of the Hadley cell, which

shifts over the southern Mediterranean (Ziv et al., 2004;

Lionello et al., 2006). Summer aridity and warming

have also been linked to the Asian monsoon intensity

(Rodwell and Hoskins, 1996). Deep convection over the

Asian monsoon region induces a westward propagating

Rossby wave generating air masses descent over the

Eastern Mediterranean (Ziv et al., 2004; Tyrlis et al.,

2013). The second process is the dry and cool northerly

winds, i.e. the Etesians, whose ventilating effect

counteracts the adiabatic warming induced by the large-

scale subsidence. These winds are generated by a sharp

pressure gradient, which builds up over the area due to

the combination of the extended Asian thermal low and

the Azores High (Rizou et al., 2018). Greece lies at the

transitional zone between these two systems, resulting

in strong Etesians over the Aegean Sea (Fig. 1 and Fig.

2). Thus, both subsidence and Etesians are related to the

monsoonal activity and lead to dry summer conditions.

Despite this, sporadic rainfall events are induced by

locally developed thermal lows associated with the

diurnal fluctuations of inland surface temperature as

well as by cut-off lows during reduced anticyclonic

activity periods (Trigo et al., 2002; Flocas et al., 2010).

3.1. Winter atmospheric

circulation patterns

Fig. 1. Atmospheric patterns affecting the Mediterranean climate dynamics. The square

depicts the Peloponnese in the Eastern Mediterranean (after Katrantsiotis et al., 2019).

4

4. The Peloponnese

4.1. Topography and Climate

The Peloponnese peninsula constitutes the southern part

of the Greek mainland covering an area of 21.549 km²

(Fig. 2 and Fig. 3). The terrain exhibits variable

morphology characterized by rugged mountains, hills,

broad plains and valleys. The peninsula is crossed by a

large mountain range, which geologically is the

extension of the Pindos Mountains stretching from the

Greek-Albanian borders (NW) to central Greece. The

average altitude in the peninsula is ca 543 m with the

maximum elevation being ca 2400 m in the Taygetos

mountain chain, in the central-southern Peloponnese.

Climatic conditions are spatially and temporally

diverse due to the irregular topography and the impacts

of different atmospheric circulation patterns. Overall,

the Peloponnese has mild, wet winters and hot, dry

summers. Most of the precipitation falls between

October and April. The NNW-SSE mountain range

across the peninsula causes a rain shadow effect on the

leeward (eastward) side of the mountain with respect to

the westerly winds (Dotsika et al., 2010). As a result,

the eastern Peloponnese is dominated by drier and

cooler conditions than SW Peloponnese (Fig. 3) (Fick

and Hijmans, 2017). The annual mean precipitation and

temperature in NE Peloponnese are 476 mm and 17.0°C

respectively, with the monthly mean temperatures

ranging from ca 27°C in July to ca 8°C in January

(Pyrgela station, close to Lerna) (Hellenic National

Meteorological Service, 2018). The annual mean

precipitation and temperature in SW Peloponnese are

780 mm and 18.0°C respectively, with the monthly

mean temperatures ranging from ca 26.5°C in July to ca

10 °C in January (Kalamata station, near Agios Floros)

(Hellenic National Meteorological Service, 2018).

The Peloponnese is located at the junction of

different atmospheric circulation patterns (NAO, NCP,

and Siberia High). During autumn, winter and early

spring, frontal depressions from the Atlantic and the

western Mediterranean produce significant precipitation

amounts associated with negative NAO and NCP

modes (Flocas and Giles, 1991). Saharan depressions

contribute to the rainfall totals as they move north–

northeast and pick up moisture over the Mediterranean.

The eastern Peloponnese receives high rainfall amounts

and occasional snowfall associated with cold northerly

winds and cyclogenesis over the Aegean Sea during

positive NCP periods. During summers, the northward

extension of the Hadley circulation causes atmospheric

stability. In addition, the area is affected by the Asian

monsoon system through modulating the intensity of

large-scale subsidence and the strength of the Etesians

(Tyrlis et al., 2013). Strong Etesians trigger cooler

conditions in NE Peloponnese compared to SW

Peloponnese located on the lee side of the mountain.

Despite the summer aridity, shortwave troughs and cut-

off lows can sporadically cause enhanced instability and

thus convective rainfall events (Xoplaki et al., 2003).

4.2. Geology and landscape development

The Peloponnese displays a composite morphotectonic

structure characterized by the presence of large grabens

and horsts bounded by E–W and NNW-SSE trending

fault zones (Fig. 4) (Fountoulis and Mariolakos, 2008; Vassilopoulou, 2010; Fountoulis et al., 2014). Inside

these neotectonic macrostructures, there are many small

morphological units of various directions. The grabens

were formed during the Pliocene-Early Pleistocene due

to the extensional deformations, which resulted in the

fragmentation and the subsidence of the bedrock along

E–W and NNW-SSE normal fault zones (Zelilidis and

Doutsos, 1992; Zelilidis and Kontopoulos, 1994). This

further allowed sea level intrusion and deposition of

Fig. 3. Distribution of mean annual precipitation in the

Peloponnese, for the period 1970-2000 (Fick and Hijmans,

2017) with the study sites i.e. Gialova Lagoon, Agios Floros

fen and Lake Lerna as well as the location of other sites

discussed in the text (after Katrantsiotis et al., 2019).

Fig. 2. Terrain map of Greece with the location of the

Peloponnese peninsula in the inset box and the subduction

zone to the south-southwest. Map modified after

scilands GmbH (www.scilands.de). Scientific Landscape.

5

marine sediments in the subsided areas along the

coastal zones of the peninsula until the early-middle

Pleistocene (Athanassas and Fountoulis et al., 2013).

Thereafter, an inversion of the kinematic regime caused

the emergence of the formerly subsiding tectonic blocks

and the uplift and erosion of marine sediments at their

present state (Fig. 4) (Marcopoulou-Diacantoni et al.,

1989; Athanassas and Fountoulis et al., 2013;

Fountoulis et al., 2014). In addition, high rates of fluvial

sedimentation, along with the retreating sea level, led to

the partial infilling of embayments and the formation of

alluvial plains such as the Messenian plain, the

Typhlomytis plain and the Argolis plain during the

Quaternary period (Fig. 4) (Kraft et al., 1975, 1977).

The Peloponnese is located in the direct vicinity of

the Hellenic arc, i.e. the convergence of the African and

the Eurasian plate, and is also characterized by a large

number of active neotectonic faults (Fig. 2 and Fig. 4).

These factors make the peninsula one of the most

tectonically and seismically active areas in Europe. It

has been subjected to destructive earthquakes like those

of 1875 (Magnitude=6, Kyparissia), 1886 (M=6.8,

Filiatra), 1903 (M=6.6, Κythira) and in 1986 (M=6.0,

Kalamata) (Fig. 4) (Papazachos and Papazachou, 2003;

Fountoulis and Mavroulis, 2013; Papadopoulos et al.,

2014). In addition to high seismicity, the coastal areas

of the peninsula have been impacted by tsunamogenic

events during the Holocene and beyond associated with

large magnitude earthquakes along the Hellenic arc

(Vött, 2007; Scheffers et al., 2008; May et al., 2012;

Willershäuser et al., 2015). For instance, historical

accounts have described one such tsunami event that

occurred on 21 July 1635 (Seyfarth, 1971). The tsunami

waves produced by a big earthquake near the west coast

of Crete, south of the Peloponnese, reached the Methoni

settlement in Pylos causing inland inundation of 2 km.

4.3. Human occupation

The Peloponnese has a long history of human activity

which extends back to the Paleolithic age. The

peninsula was an important center for the establishment

and evolution of ancient Greek civilization, comprising

a wide and well-documented spectrum of early farming

communities, palatial economies and city-states such as

those of Mycenae and Olympia (Weiberg et al., 2016).

The region is well-documented in historical sources. A

large number of archaeological field surveys have been

carried out in this region, tracing long-term sites and

settlement patterns (Alcock and Cherry, 2004). Overall,

the Peloponnese has been the focus of multi-

disciplinary studies aiming to develop an integrated

long-term narrative of the interactions between humans

and environment in this region (Weiberg et al., 2016).

5. Description of study sites

Three sites were studied in this thesis; the Agios Floros

fen and the Gialova Lagoon in SW Peloponnese and the

Lake Lerna in NE Peloponnese (Fig. 3). The selection

of these sites was based on three criteria. (1) They are

located in different climatic zones of the peninsula,

which is important to trace regional climatic differences

and common patterns during the Holocene. 2) The

studied sites are situated in geomorphologically

sheltered positions, which favor sediment deposition at

a constant rate. These continuous deposits most likely

contain uninterrupted records of the Holocene climatic

changes. (3) Hydrological conditions in these sites are

influenced by climate factors i.e. the balance between

precipitation/freshwater input and evaporation rate. (4)

The sites are located close to important archaeological

places. The data from this thesis will help future studies

to place archeological findings in a climate perspective.

5.1. Messenian plain/Agios Floros fen

The Agios Floros fen is located in the central-eastern

Messenian plain, which is a tectonic graben bounded by

NNW–SSE normal faults (Fig. 5). The bedrock consists

of Mesozoic and Early Cenozoic limestones covered

with Pliocene–early Pleistocene marine sediments,

Pleistocene alluvial deposits as well as Holocene peat

accumulations (Perrier, 1975). The fen was developed

during the Holocene in a small shallow basin, with a

maximum depth of 2 m and an outlet to the south via

the Pamisos River (Fig. 5). The fen is located less than

one kilometer from the outlet of karst springs on the

western slopes of the Taygetos Mountain (Fig. 6). The

springs are connected to a NNW striking normal fault

system, and are the main water sources of the Pamisos

River (Fig. 5). The underlying karst aquifer acts as a

reservoir of rainfalls, and hence spring discharges are

modulated by the annual precipitation amount. Water

level changes in the fen are mainly attributed to surface

runoff, spring water outflow and the evaporation rate.

Fig. 4. The main marginal fault zones of the post-Alpine

basins in the Peloponnese (after Fountoulis et al., 2014).

6

Until the middle of the last century, large areas of

the river valley were covered by swamps. Thereafter,

the valley was drained for agricultural activities (Lyras,

2011). The cultivated area currently consists of Olea

europaea. The vegetation in the fen and along the river

banks is characterized by reed (Phragmites australis,

Arundo donax), shrubs and trees e.g. Salix fragilis,

Platanus orientalis, Nerium oleander. The springs and

ponds are dominated by pure aquatic vegetation e.g.

Nymphaeetum albae and Potamogeton natans. The

hills are covered by dwarf-shrubs and sclerophyllous

evergreen shrubs and trees (Papazisimou et al., 2005).

The central Messenian plain is poorly investigated.

Previous studies have mainly focused on the palaeo-

geographical evolution of the lower Messenia plain

based on pollen and foraminifera and with specific

reference to archaeological evidence from settlements

(Kraft et al., 1975; Engel et al., 2009). The only

available study from the central Messenian plain is

based on a low resolution pollen record providing

evidence for Holocene vegetation shifts and peat

formation in Agios Floros (Papazisimou et al., 2005).

5.2. Gialova Lagoon

The Gialova Lagoon is a shallow coastal ecosystem

located in the western Messenia, SW Peloponnese (Fig.

7). It is a part of a small active depression, which

consists of the Navarino embayment to the south, and

the Tifflomitis alluvial plain to the north of the lagoon

(Fig. 7 and Fig. 8). The bedrock consists of Cretaceous

and Paleocene/Eocene limestones (IGME, 1980). The

post alpine deposits are composed of Pliocene marine

sediments, covered with Holocene fluvial sediments.

The Gialova Lagoon is located at 0-1 m a.s.l.

(meters above sea level) and linked to the adjacent

embayment via a narrow artificial inlet, which cuts

through a sandy barrier system (Fig. 7 and Fig. 8). To

the west, there is a belt of sand dunes, which separates

the lagoon from the Voidokilia Bay and the Ionian Sea.

The swamp area to the east has been drained for

agricultural purposes. The catchment area to the north is

mainly covered with floodplain sediments (Fig. 7).

The lagoonal environment was established at ca

5300-4200 cal BP (calibrated years before present) and

gradually replaced by a completely isolated lagoon until

ca 3300 cal BP (Emmanouilidis et al., 2018). After the

isolation, the physicochemical parameters of the lagoon

have mainly been governed by the balance between

precipitation/freshwater input via rivers and evaporation

rate (Papakonstantinou, 2015). The lagoon has a surface

area of ca 2.5 km2 with water depths ranging from 0.5

to 1m. The lowest water depth and the highest salinity

occur during summers. The lagoon is also characterized

as eutrophic in April and hypereutrophic in August with

pH raging from 7 to 9 and the highest dissolved oxygen

mainly occurring during winters (Koutsoubas et al.,

1997; Bouzos et al., 2002; Papakonstantinou, 2015).

The lagoonal bottom is sparsely covered with the

salt tolerant grasses, Ruppia cirrhosa, and the seagrass,

Cymodocea nodosa, mainly close to the communication

channel with the Navarino marine embayment

(Tiniakos and Tiniakou, 1997; Papakonstantinou,

2015). The vegetation around the lagoon generally

consists of salt-tolerant plants (e.g. Salicornia europea),

halophyte and rush plant communities (e.g. Schoenus

nigricans and Juncus maritimus), rhizome geophyte

(e.g. Ammophila arenaria), phrygana communities (e.g.

Sarcopoterium spinosum) evergreen shrubs and trees

Fig. 5. Geological map of the Messenian plain (after Perrier,

1975) with the location of the Agios Floros fen and the coring

site, close to the karst springs (blue dot).

Fig. 6. The Agios Floros wetland with the location of the

coring site close to the flooded fields.

7

Fig. 8. Gialova Lagoon. The Voidokilia Bay to the west.

The sandy barrier and the Navarino embayment to the south.

(e.g. Juniperus phoenicea, Thymus capitatus), mastic

tree (Pistacia lentiscus), perennial grasses, sedges and

plants (e.g. Phragmites australis) and cultivations (e.g.

Olea europea) (Zangger et al., 1997; Korakis, 2006).

The area surrounding Gialova Lagoon has a long

history of human presence especially after 5000 cal BP

(Kraft et al., 1980). The Navarino area functioned as

one of the most important centers of the Mycenaean

civilization at 3600-3000 cal BP (Zangger et al., 1997).

Intensive settlement and land use are also inferred from

the Hellenistic and Roman times (2500-1400 cal BP).

Previous studies have mainly focused on the

palaeoenvironmental evolution of the Navarino area

based on pollen and foraminifera in sediment cores

(Kraft et al., 1980; Zangger et al., 1997; Avramidis et

al., 2015; Willershäuser et al. 2015; Emmanouilidis et

al., 2018). In addition, special attention has been paid to

the interplay between landscape development, changes

in vegetation and societal dynamics in the area around

the lagoon (Kraft et al., 1980; Zangger et al., 1997).

5.3. Lake Lerna

The Lerna site is located a few meters from the coast of

the Gulf of Argos, within the Argive Plain, in NE

Peloponnese (Fig. 9 and Fig. 10). The Gulf of Argos

and the Argive plain represent a fault-bounded NW-SE

tectonic depression. The bedrock exposed to the east

and west of the plain is composed of Mesozoic/Eocene

limestones, ophiolites and flysch (van Andel et al.,

1990). Plio-Pleistocene marls and fluvial conglomerates

occur at lower elevations around the plain. The low-

lying areas consist of Holocene coastal and alluvial

deposits punctuated by marine sediments. The plain is

bordered by NW-SE faults with secondary fault systems

trending NE-SW and E-W (Maroukian et al., 2004).

The ancient Lake Lerna was formed behind a beach

barrier at ca 8300 cal BP, with maximum extension at

ca 6000 cal BP (Zangger, 1991). This barrier was

created by the Inakhos River propagation and

dispersion of sediment along the shore. The Lake was

isolated from the sea and supplied with freshwater from

the Erasinos River throughout the Holocene (Fig. 9)

(Finke, 1988; Zangger, 1991). At ca 5000-4000 cal BP,

Fig. 7. Geological map of the Navarino area (IGME, 1980)

with the location of the Gialova Lagoon and the coring site

in the central part of the lagoon.

Fig. 9. Geological map of the Argive Plain. The black outline

depicts the extension of the Ancient Lake Lerna (after van

Andel et al., 1990). The black dot shows the location of the

coring site.

Fig. 10. The Lerna wetland with the location of the coring site

to the south inside the reed belt.

W S

S N

8

the eastern part of the lake was filled with sediments

while the western part remained a shallow water body

until modern times (Zangger, 1991; Jahns, 1993).

The Lerna site is currently a wetland which

partially gets flooded during the wet season. The water

regime is also determined by numerous streams and

springs. The vegetation in the wetland consists of reeds,

(Phragmites australis and Arundo Donax), perennial

herbaceous plants (e.g. Typha latifolia) with emergent

and floating plants (Cladium mariscus and Nymphaea

sp.) mainly occurring in small ponds (Jahns, 1993;

Pantazopoulou, 2015). The area around the wetland is

dominated by orange tree and olive cultivations. The

non-cultivated land comprises phrygana and evergreen

shrubs (e.g. Quercus coccifera, Pistacia lentiscus) and

some riparian vegetation (e.g. Eucalyptus, Salix)

(Pantazopoulou, 2015). The mountain areas are mainly

dominated by the holm oak (Quercus ilex) and ever-

green trees (e.g. Abies cephalonica and Pinus nigra).

The Argive plain constitutes an archeologically

important area with famous Bronze Age settlements,

such as Mycenae, Tiryns and Lerna (Jahns, 1993; Cline,

2010; Weiberg et al., 2016) and the city-state of Argos

during the historical periods (Pariente and Touchais,

1998). The archaeological site of Lerna (ca 4 km SW of

the coring site) was used from the Neolithic period and

throughout the Bronze Age, with some activities in the

historical periods (Zangger, 1991; Jahns, 1993;

Wiencke, 2010). The site is particularly known for its

Early Bronze Age remains (ca 4700-4200 cal BP).

Paleoenvironmental studies in the Argive plain are

relatively old (early 90s) focusing on the Holocene

shore displacement of the Gulf of Argos and vegetation

shifts around the Lerna site (Kraft et al., 1977; Zangger,

1991; Jahns, 1993). Attempts have also been made to

bring together information from different archives and

archaeological records to explore links between societal

dynamics and landscape development (e.g. Zangger,

1991; Jahns, 1993; Cline, 2010; Weiberg et al., 2016).

6. Material and methods

The studies presented in this thesis are based on down-

core fossil data extracted from sediment cores. A

multiproxy approach was applied to strengthen

paleoclimatic interpretation. The methods involved

several steps. The field work planning and performance

included the examination of sites for suitable coring

spots and the recovery of cores. The chronologies of the

cores were based on accelerator mass spectrometry

(AMS) radiocarbon dating of macrofossils and bulk

samples. The laboratory work further involved the use

of various techniques to extract and analyze biological

and geochemical proxies. In particular, the proxy

methods included diatoms, n-alkanes and their δ13C and

δD composition, bulk geochemistry and XFR core

scanning data. A theoretical framework for each proxy

and further details for the laboratory and analytical

work are given both here and also in the papers (I-V).

6.1. Field work

Lake and lagoonal sediment sequences were collected

from each studied site using a hand-operated Russian

peat corer. The coring was performed by recovering

contiguous core segments at successively greater depths

on the same spots. In particular, during our field work

in October 2013, a 7.5 m long core was retrieved from

the Agios Floros fen, ca 2 km west of the homonymous

village, close to karst springs (Fig. 5 and Fig. 6) (N

37°10'05.25" E 22°01'05.61"; 13 m a.s.l.). During the

same field campaign, a 2.6 m long core was recovered

from the central part of the Gialova Lagoon (Fig. 7 and

Fig. 8) (N 36°57'48.59" E 21°40'16.65"; 1 m a.s.l). The

recovery of the core was performed from a boat. The

uppermost 10 cm was lost during sampling due to the

high water content of sediments. For the Agios Floros-

Gialova campaign, the Russian corer had a size of 0.5

m length and 4.5 cm diameter. Field work was

conducted at the ancient Lake Lerna in December 2016.

A 5 meters long core was sampled with a Russian corer

of 1 m length and 4.5 cm diameter (Fig. 9 and Fig. 10)

(N 37°34'57.66" E 22°43'57.60"; 1 m a.s.l.). The

sequences were examined in the field for their physical

characteristics such as lithology, color, boundaries and

internal structure. The lithological descriptions were

later discussed in relation to proxy data. Thereafter, the

cores were placed into rigid plastic half-tubes, wrapped

in plastic film and were transported to the University of

the Peloponnese, in Kalamata, Greece and to Stockholm

University for subsampling and laboratory analysis.

6.2. Proxy description and laboratory work

The sediment cores were visually examined in more

detail for their physical characteristics in the laboratory

and thereafter sub-sampled with a resolution of 1 cm.

The subsampling for the Agios Floros and Gialova

cores was performed at the laboratory of Archaeometry

at the University of the Peloponnese. The sub-samples

were sealed in plastic bags and transported to

Stockholm University. The subsampling for the Lerna

core was performed at the Department of Physical

Geography, Stockholm University. All the samples

were kept in storage at 4°C until they were analyzed.

6.2.1. Radiocarbon dating

Radiocarbon dating is the most widely used method to

establish an age-depth relationship for sediment cores.

The principles of the radiocarbon dating have been

discussed extensively (e.g. Broecker and Kulp, 1956;

Olsson, 1991; Björck and Wohlfarth, 2001). Briefly, the

radioactive carbon isotope (14C) is formed in the upper

atmosphere, where cosmic ray neutrons react with 14N

atoms. The newly formed 14C is rapidly oxidized to 14CO2, dispersed through the atmosphere and

subsequently enters the Earth's plant and animal life

through photosynthesis and the food chain. Plants and

animals, which take up 14C during their lifetimes, exist

in equilibrium with the atmospheric 14C concentration.

9

When the organism dies, absorption of 14C ceases, and

the amount of 14C gradually decays at a constant rate.

Carbon-14 has a half-life of 5730±40 years, meaning

that the concentration halves every 5730 years. By

measuring the 14C content left in a sample, and

particularly the ratio of 14C against the stable forms of

carbons, the time since the organism died can be

estimated. However, the production of carbon isotopes

varies both spatially and temporally, and therefore

calibration curves need to be used to covert radiocarbon

dates into calendar years (Olsson, 1991; Fairbanks et

al., 2005). The radiocarbon calibration curve for the

northern hemisphere (IntCal13) is extended back to

50.000 cal BP and is based on 14C measurements of

known-age tree-ring, plant macrofossils, speleothems,

corals, and foraminifera samples (Reimer et al., 2013).

Macrofossils from terrestrial plants, which fix only

atmospheric CO2, are considered to be the most

reliable material for 14C dating (Olsson, 1991; Björck

and Wohlfarth, 2001). However, a source of uncertainty

is sometimes related to the potential input of younger or

older terrestrial plant macrofossils into the sediments

through erosion and bioturbation (Björck and

Wohlfarth, 2001). In the absence of terrestrial remains,

aquatic plant macrofossils and bulk sediments can be

used for 14C dating with the caveat that these materials

can be influenced by the reservoir effect and/or hard

water effect. These effects are associated with the 14C-

depleted carbon in water compared to atmospheric CO2

and/or the input of pre-aged carbon via rivers and

groundwater. The assimilation of old carbon by aquatic

plants results in too old apparent ages (Olsson, 1983).

Core chronology – Age depth modelling

Sediment samples throughout the cores were soaked in

10% KOH and washed with a fine jet of water through

a 0.250 mm sieve. The residues were dispersed in a

petri dish filled with distilled water. Macrofossils and

charcoal pieces were extracted under a stereo

microscope using soft tweezers. The dating materials

were placed in glass vials filled with distilled water. In

the Lerna core, bulk sediments were also dated in some

depths due to the absence of seeds. Accelerator mass

spectrometry (AMS) 14C dating of the samples was

performed in Poznan Radiocarbon Laboratory, Poland,

Beta analytics and in the Tandem Laboratory, Uppsala.

The calibration of 14C ages and the construction of

age depth-models were performed with 2σ confidence

intervals using the CLAM 2.2 program (Blaauw, 2010)

and the IntCal13 calibration curve (Reimer et al., 2013)

in the software R.3.1.1 (R Development Core Team,

2013). All calibrated ages are given in years before

present (cal BP). Age-depth models were constructed

by using linear interpolation between the midpoints of

2-sigma calibrated age ranges and extrapolating to the

base and top of the cores. Weighted average estimates

and accumulations rates (cm-1) were obtained from

every depth based on the entire calibrated distribution

of all dates and also the applied model (Blaauw, 2010).

6.2.2. Siliceous microfossils

Diatoms

Diatoms are microscopic unicellular algae encased in a

cell-wall, known as frustules. The cell wall consists of

rigid amorphous silica which has high preservation

potential in sedimentary environments. The application

of diatoms in paleoenvironmental studies has a long

tradition (Stoermer and Smol, 2010 and references

therein). This is because the siliceous frustule displays

specific morphological characteristics enabling diatom

identification into lower taxonomic level (Round et al.,

1990). Besides, diatoms have well-defined ecological

preferences and high species diversity. These single-cell

organisms reproduce quickly and are sensitive to a

range of environmental factors such as salinity, water

depth and nutrient availability (Battarbee et al., 2001).

Therefore, diatom species composition changes in fossil

records due to shifts in one of these parameters can be

used to reconstruct paleo-hydrological conditions.

Although diatoms are considered as excellent

indicators of past environmental conditions, the quality

of reconstruction usually relies on the degree of diatom

preservation, which can be a major taphonomic issue

(Ryves et al., 2013). Diatom valves are sometimes

absent or poorly preserved in sediments. The

composition of fossil assemblages can be affected by

various chemical and physical processes including

dissolution, resuspension and bioturbation (Snoeijs and

Weckström, 2010). Poor preservation of diatom species

due to silica dissolution and valve fragmentation is

common in shallow freshwater and saline ecosystems

(Ryves et al., 2006). This could bias diatom

assemblages to more resistant taxa (Barker, 1992).

Other potential limitations when interpreting diatom

records include misidentification of taxa, taxonomic

problems and limited ecological knowledge of species.

Phytolith/Diatom ratio

Phytoliths are siliceous remnants of the decomposition

of plant material with highly distinctive shape that can

be identified to species level (Piperno, 2006). Upon

plant death and decay, phytoliths are preserved in the

depositional environment and can be used to examine

vegetation history (e.g. Rovner, 1971; Delhon et al.,

2003; Finné et al., 2010). The phytolith/diatom ration

has been used as an indicator of water level changes

and shifts in the distance between sampling site and

shore (Chalié and Gasse, 2002). Small distances and

shallow water levels likely favor the high abundance of

phytoliths in the site (Holmgren et al., 2012). Deep lake

and large distance likely prevent phytoliths of terrestrial

and telmatic origin from reaching the sampling site. The

phytolith production rate, however, depends on the

vegetation type in the catchment area. Therefore, the

phytolith/diatom ration should be used as a complement

tool to the reconstruction based on the habitat diatom

groups. The latter provides more qualitative information

on the past lake level changes (Chalié and Gasse, 2002).

10

Siliceous microfossil extraction and analysis

The sediment cores retrieved from the three studied

sites were first examined for diatom presence. Sediment

samples were taken and analyzed from each litho-

stratigraphic unit throughout the cores. The samples

were prepared according to the standard method

described below (Battarbee, 1986). The Agios Floros

sediment core contained abundant diatoms, and

therefore was proceeded for detailed analysis. The

samples from the Gialova Lagoon and the Lake Lerna

were deprived of diatoms and the cores from these two

sites were analyzed for other geochemical proxies.

Around 2 g of wet sediment with a resolution of 4–

6 cm were used for diatom analysis in the Agios Floros

core. The samples were treated with 10 % HCl to

remove carbonates. Organic compounds were oxidized

by using 17% H2O2. To minimize vivid chemical

reactions, the samples were left at room temperature

overnight and boiled on water-bath the following day.

After oxidation, the suspensions were repeatedly

decanted at two-hour intervals from 100 ml beakers

until most of the clay particles were removed. Distilled

water with NH3 was added to disperse the remaining

clay particles. The residues were transferred to 5 ml

tubes and a volume of the residue was extracted and

spread out evenly on the cover-glass. The prepared

samples were dried onto cover-slips and mounted on a

microscope slide using Naphrax® to increase refraction

index. Counting were carried out under a light

microscope at a magnification of X1000 using oil

immersion to further increase the refraction index.

In total, 125 samples were analyzed throughout the

Agios Floros core and a minimum number of 300

valves were counted in each slide. Detailed taxonomic

descriptions were performed using SEM. Diatom

species were grouped into classes based on their water

depth preferences (benthic/planktonic/subaerophilous).

Identification and ecological classification were

primarily based on Krammer and Lange-Bertalot (1986,

1988, 1991a, 1991b). To investigate the impact of

dissolution in the diatom assemblage, a dissolution

index was calculated after classifying the valves as

intact versus dissolved (F index = dissolved/intact +

dissolved valves; Currás et al., 2012; Ryves et al.,

2001). Dissolved valves were considered all the valves

showing sign of dissolution under the LM; valves with

margins and striation missing, transparent and

featureless valves and also broken valves with signs of

dissolution (dissolved fragments) (Barker, 1992). The

dissolution index varies between 0 and 1; with a score

of 1 representing samples dominated by dissolved

valves. In addition, the number of phytoliths was

counted along the same transects. No attempt was made

to distinguish the different phytolith morphotypes. A

phytolith index (phytolith/diatom + phytolith) was

calculated with values close to 1 representing samples

dominated by high phytolith amounts. The phytolith

index, along with the visual inspection of clastic debris

content in each sample, was used as an additional

indicator of lake level changes (Chalie and Gasse, 2002;

Holmgren et al., 2012). The results are presented as

stratigraphic diagrams depicting the relative abundance

of diatom species, the dissolution and phytolith indices

as well as the clastic debris content. The graphs were

constructed using the Tilia program version 1.7.16,

(Grimm, 1991, 2004). Zones of the diatom assemblage

were defined performing constrained incremental sum-

of-squares cluster analysis (CONISS; Grimm, 1987).

6.2.3. Organic geochemistry

Organic matter (OM) in sediments consists of mixture

of biogeochemical components, derived from various

autochthonous and allochthonous sources in and around

aquatic ecosystems (Meyers and Teranes, 2001). These

substances retain paleoenvironmental information

regarding the sedimentary OM origins and also the

abundance of different biota from which the organic

compounds are derived (Meyers, 2003). Therefore, the

identification of different OM sources is important for

paleoenvironmental reconstructions. The study of OM

can be performed in bulk samples that contain a mixture

of organic compounds, and/or at molecular level where

each compound can be attributed to a specific source.

n-Alkanes

The analysis of lipid biomarkers, particularly aliphatic

saturated hydrocarbons (n-alkanes), has become a

widely applied tool in paleo-environmental studies (e.g.

Pu et al., 2010; Zech et al., 2011; Aichner et al., 2018).

This is because n-alkanes are characteristic of specific

sources, constitute the most abundant biomarkers in

sediments and also are relatively easy to purify and

analyze (Peters et al., 2005; Grice and Eiserbeck, 2014).

Besides, due to their structure consisting of strong and

localized C–C and C–H bonds, n-alkanes are the most

resistant lipid compounds to degradation, and hence are

preserved in sediments over geological time-scales

(Labinger and Bercaw, 2002; Peters et al., 2005).

Different organisms produce n-alkanes with distinct

carbon chain-lengths (Bush and McInerney, 2013 and

references therein). The down-core carbon chain-length

distributions can therefore provide evidence for the

sedimentary OM origin (Giger et al., 1980; Meyers,

1997). Aquatic algae and bacteria are the primary

producers of short-chain n-alkanes (C17 to C21)

(Cranwell et al., 1987). Mid-chain homologues (C23 to

C25) are mainly attributed to submerged aquatic

macrophytes and/or mosses (Baas et al., 2000; Ficken et

al., 2000). Long chain n-alkanes (C27 to C35) are

typically produced as part of the epicuticular leaf waxes

of terrestrial higher plants (Eglinton and Hamilton,

1967). In particular, woody plants (trees and shrubs)

have been shown to produce C27 and C29 n-alkanes,

while herbaceous plants and grasses tend to contain a

relatively higher amount of C31 or C33 n-alkanes

(Cranwell, 1973; Meyers and Ishiwatari, 1993).

However, there is a large variation in the chain-length

distribution within the different plant groups attributed

to physiological and environmental factors (Bush and

11

McInerney, 2013). Some studies have shown that

woody plants, such as Olea europea, can synthesize

abundant n-C33-C 35 alkanes under moisture deficit (e.g.

Pierantozzi et al., 2013). Aquatic plants have also been

found to produce long-chain n-alkanes in shallow lakes

(Aichner et al., 2010). Overall, the n-alkane distribution

should not be used indiscriminately to constrain the OM

sources. This method should be combined with the δ13C

analysis of n-alkanes and ideally complemented with a

survey of n-alkane production of the local vegetation.

n-Alkane extraction and quantification

Lipid extraction was performed on freeze-dried and

homogenized sediment samples (1-15 g), which were

taken at every 5 cm throughout the sediment cores. The

samples were then mixed with organic solvents

(dichloromethane: methanol 9:1 v/v), placed in a sonic

bath for ca 20 min and centrifuged at 3000 rpm. Afterwards, the lipid extract was recovered into a glass

tube. This procedure was repeated three times. The

extracts were combined into a total lipid extract dried

under a nitrogen gas stream (N2), re-dissolved in hexane

and adsorbed onto precombusted silica gel. Solid phase

extraction was performed in order to obtain aliphatic

hydrocarbon fractions using pipette columns filled with

glass wool, silica gel and the (adsorbed) lipid

compounds on top. The fractions were extracted by

flushing the columns with hexane (3×column volume).

In some samples from the Agios Floros and Lerna cores

elemental sulfur was detected during the gas

chromatography-mass spectrometry (GC-MS) analysis

described below. To remove sulfur and obtain fractions

with only saturated hydrocarbons, the aliphatic

hydrocarbon fractions were eluted with hexane through

pipette columns filled with glass wool, activated copper

(prepared by rinsing with a sequence of HCl (1 M),

isopropyl alcohol, dichloromethane and hexane) and

10% silver nitrate (AgNO3)-coated silica gel. The final

fractions with hexane were then stored in a freezer.

For the n-alkane identification and quantification

hydrocarbon fractions were analyzed by a Shimadzu

GCMS-QP2010 Ultra gas chromatography-mass

spectrometry (GC-MS). The instrument was equipped

with an AOC-20i autosampler and a split-splitless

injector operated in splitless mode. For separation, a

GC column with the following dimensions was used:

30m×0.25mm×0.25 μm (Zebron ZB-5HT Inferno). The

GC oven was programmed for a temperature increase

from 60 °C to 180 °C by 20 °C/min, then up to 320 °C

by 4 °C/min, followed by a hold time of 20 min.

Quantification was performed with an external

calibration curve, produced by analyzing regularly a n-

C21-40 alkane standard solution (Fluka Analytical) at

different concentrations. The software MS Solution

4.11 (Shimadzu) was used for compound identification

and area integration of the relevant peaks. Compound

identification and area integration of the relevant peaks

were performed with the GC5MS Solution software

version 4.11 (Shimadzu). The results are reported in

graphs showing the n-alkane abundances throughout the

sediment cores. The graphs were constructed using the

Tilia program version 1.7.16 (Grimm, 1991; 2004).

Three indexes were calculated based on the C17-C35

homologues. The carbon preference index (CPI) was

calculated as: CPI = Σodd / Σeven (Wang et al., 2003). The

average chain length (ACL) was determined as: ACL =

Σ (n * Cn) / Σ Cn where Cn is the concentration of odd

chain n-alkanes (Tanner et al., 2010). The Paq index

(proxy for aquatic macrophytes) was calculated as: Paq

= (C23 + C25) / (C23 + C25 + C29 + C31) (Ficken et al., 2000).

Stable carbon and hydrogen isotopes

Organic compounds mainly consist of molecules

containing carbon and hydrogen, and therefore the

stable isotopes of these two elements are studied in

organic geochemistry (Brocks and Summons, 2014).

Stable isotopes are atoms of the same chemical element

with the same number of protons and electrons (i.e.

atomic number) but different number of neutrons (i.e.

mass number). Carbon has two stable isotopes 13C and

12C, the latter being the lighter and most abundant. 1H

(H) and 2H or D (deuterium) are stable isotopes of

hydrogen with deuterium being the heavier and rarer

(Wieser and Brand, 2017). Since the various isotopes of

an element have different mass, their chemical and

physical properties are slightly different, a phenomenon

called isotope effect. There are two types of isotope

effects - equilibrium and kinetic - which cause isotopic

fractionation i.e. partial separation of isotopes of the

same element between two substances during physical

or chemical processes (Kendall and Caldwell, 1998).

Heavy isotopes form stronger bonds and react, diffuse

or evaporate slower compared to light ones (kinetic

fractionation). At equilibrium, heavy isotopes tend to

be concentrated in phases with stronger chemical bonds

(low energy state: solid phases) than the light isotopes,

which are more volatile (equilibrium fractionation).

Due to the low abundance of the heavy isotopes,

stable isotopes are expressed as the ratio of the rare

(heavy) isotope to the common (light) isotope compared

to the same ratio in an international standard using

the delta notation (equation 1). The isotopic

composition is reported as parts per thousand or 'per

mil' (‰) with positive values indicating that the sample

has a higher ratio than the standard and vice versa.

δ = (Rsample / Rstandard -1) * 1000 (1)

The internationally reference standards are: Vienna Pee

Dee Belemnite (VPDB) for carbon isotopes (δ13C, with

R=13C/12C) and Vienna Standard Mean Ocean Water

(VSMOW) for hydrogen isotopes (δD, with R=D/H).

δ13C values of photosynthetic organisms

Plants in terrestrial environments absorb atmospheric

CO2 as the sole carbon source for photosynthesis. The

resulting isotopic composition of plants thus depends on

12

the 13C content of carbon source and the isotope effects

during assimilation of CO2 and biosynthesis in the

plants (Hayes, 1993; Chikaraishi, 2014). The variation

in the 13C content of atmospheric CO2 was minimal

during the late Quaternary, mainly ranging between -

6‰ and -8‰ (Jasper and Hayes, 1990; Schmitt et al.,

2012; Bauska et al., 2016). Therefore, changes in the

isotopic composition of terrestrial plants can largely be

associated with fractionation primarily attributed to

kinetic isotope effect. This takes places in two steps and

results in plant biomass being more depleted in 13C than

CO2 (Fig. 11) (Farquhar et al., 1989; Chikaraishi,

2014). In the first step, 12CO2 preferentially diffuses

through the stomata into plant cells due to its lighter

mass and higher velocity. In the seconds step, the

isotopic fractionation is associated with fixation of

inorganic carbon via carboxylation. The fractionation

extent depends on the photosynthetic pathway

(O’Leary, 1988). In particular, bulk biomass of C3

plants fixes CO2 via the Calvin-cycle, which shows a

greater discrimination against 13C than the Hatch-Slack-

Cycle. The latter is used by C4 plants, which

consequently have less negative bulk δ13C values (from

−9 to −17‰) than C3 plants (between −23 and −34‰)

(O’Leary, 1988; Chikaraishi and Naraoka, 2001; Tipple

and Pagani, 2007). Some plants utilize a third photo-

synthetic pathway, the so-called Crassulacean acid

metabolism (CAM), producing intermediate δ13C values

between those of C3 and C4 plants (Bender, 1971).

Algae and aquatic plants can selectively use

dissolved CO2 and/or bicarbonate (HCO3−) as carbon

sources (Chikaraishi, 2014). This carbon csignal is

altered by fractionation processes leading to more

negative δ13C values compared to the carbon sourse

(Fig. 11). Moreover, there is a substantial difference in

the isotopic composition between CO2 and HCO3− due

to equlibrium effect. Carbon isotopic fractionation in an

equilibrium system CO2 (gas), HCO3− (dissolved) and

CaCO3 (solid) is dependent on the temperature; the

magnitude of fractionation decreases with increasing

temperature (O’Neil, 1986). In this case, the heavier

isotope tends to remain in the liquid phase (Gonfiantini,

1986). The equilibrium reaction between CO2 and

HCO3− leads to the 13C enrichment of HCO3

− by as high

as 10% compared to CO2 (Fig. 11) (Peters et al., 2005;

Chikaraishi, 2014). Aquatic plants and algae can switch

from assimilation of dissolved CO2 to HCO3−, if the

former decreases (under high productivity or alkalinity).

This results in higher δ13C values of the assimilating

organism (Prins and Elzenga, 1989; Mead et al., 2005).

δ13C composition of n-alkanes

The δ13C compositions of individual n-alkanes can be

used to differentiate between different plant types and

better track the OM sources (Chikaraishi and Naraoka,

2003; Mead et al., 2005; Fang et al., 2014). In addition

to fractionation process related to plant type, another

fractionation step is included during lipid synthesis.

This results in more negative δ13C values of lipids by

3.6‰ on average compared to bulk biomass (Fig. 11)

(Park and Epstein, 1961; Collister et al., 1994). The

δ13C composition of individual n-alkanes is sensitive to

plant type, mainly due to the differences in the isotopic

fractionation extent between growth forms (e.g.

angiosperms v. gymnosperms, trees v. grasses) and

photosynthetic pathways (e.g. C3 v. C4) (Collister et al.,

1994; Diefendorf and Freimuth, 2017). The 13C content

of individual n-alkanes can thus provide important

information regarding the OM sources. Shifts in the

carbon source and abundance of aquatic macrophytes

will be recorded by the mid-chain n-alkanes and

changes in the algal and microbial primary production

mainly by the short-chain n-alkanes. Analogously,

terrestrial vegetation changes will be recorded by the

δ13C profiles of long-chain homologues. In the

Mediterranean region, C4 grasses are generally rare

(Cross, 1980). Consequently, shifts to higher δ13C

values of these n-alkanes (> −26‰) in lake sediments

can be interpreted as an increased contribution of

aquatic plants to OM producing high amount of long-

chain homologues (Fig. 11) (Aichner, 2009; Liu et al.,

2015). In addition, other environmental conditions can

influence the n-alkane δ13C values. Plants close their

stomata under highly saline or dry conditions to

preserve water. This results in a decreased rate of

photosynthetic CO2 assimilation leading to higher δ13C

values (Wooller et al., 2007; Douglas et al., 2012).

δD in precipitation

Hydrogen isotopes are the principal components of

various compounds in the hydro-, geo- and biosphere.

Their conservation in proxy archives provides

information of past hydroclimate changes (Gat, 1996;

Darling, 2011; Sessions, 2016). The basis for these

paleoclimate investigations relies on the fact that the

D/H ratio of precipitation (δDprecip) as well as in aquatic

ecosystems varies substantially over space and time in

response to various climatic and environmental changes

Fig. 11. δ13C values for different plants, their leaf waxes

and carbon sources (after Mouk, 2001 and Aichner, 2009).

13

(Dansgaard, 1964). The stable isotopes of hydrogen

exhibit the largest relative mass difference, and

consequently have different physical and chemical

properties; e.g. the heavier isotope has lower mobility.

This leads to isotopic fractionation processes, and hence

in a large variation in the D/H ratio accompanying the

physical conversion of water between the solid, liquid

and vapor phases (Fig. 12) (Craig, 1961; Gourcy et al.,

2005). In particular, evaporation discriminates against

the heavier isotope (lighter isotope evaporates faster)

resulting in more negative D/H ratios in water vapor

compared to original water source. On the contrary, the

process of condensation discriminates in favor of

the heavier isotope leading to more positive D/H ratio

in water vapor. As the heavier isotope is preferentially

condensed to rain droplets, the resulting rain is enriched

in D relative to the remaining vapor, which becomes

more depleted in D with subsequent rainfall events.

Several geographical and climatic factors, such as

the amount effect and the temperature effect, the

elevation and distance from the shore, can influence the

δDprecip values (Fig. 12) (Dansgaard, 1964). Decreasing

temperatures with increasing elevations lead to

enhanced condensation, and therefore to progressive

depletion of precipitation in heavy isotopes. This

altitude effect accounts for -1 to -4 ‰ per 100 m for

deuterium (Holdsworth et al., 1991). Additionally,

progressive depletion in heavy isotopes with increasing

distance from the ocean predominantly occurs in mid-

latitudes and this is known as the continental effect.

(Fig. 12). For Europe, the inland gradient of D content

amounts to -3.3 ‰ per 100 km in winter and -1.3‰ per

100 km in summer (Rozanski et al., 1982). In high and

middle latitude continental regions dominated by strong

temperature variability, the δDprecip values are primarily

influenced by the temperature effect (Bowen, 2008).

Lower mean air temperatures lead to lower δDprec

values. In tropical region dominated by distinct dry and

wet seasons, the δDprecip values are mainly influenced

by the amount-effect. As rainfall intensities increase and

the heavier isotope rains out, isotopic fractionation

decreases with the ongoing condensation leading to

lower D/H ratio values of meteoric water (Dansgaard,

1964; Gourcy et al., 2005). In addition, two processes

contribute to the amount effect (Fig. 12) (Risi et al.,

2008). The first is the vapor recycling process which

includes the input of already depleted vapor into the

sub-cloud layer from the unsaturated downdrafts. The

latter becomes more intense with stronger convection.

In the second process, the amount effect is attributed to

the low re-evaporation rate of falling rain and the more

efficient diffusive exchanges between raindrops and the

surrounding vapor at high precipitation rates (Risi et al.,

2008). Model simulations suggest that the amount

effect in low-latitude regions is observed if precipitation

variations result from changes in the large-scale vertical

motions (Bony et al., 2008). This is further confirmed

by modern observations showing a link between

monthly δ18O with large-scale, not local, precipitation,

and especially changes in the location and convection

intensity in the source regions of moisture (Conroy et

al., 2013; Tang et al., 2015). The amount effect has also

been shown to play an important role in water isotopes

at the middle latitudes, with lower δD values mainly

resulting from higher amounts of precipitation during

summer (Dansgaard, 1964; Lawrence and White, 1991).

All these effects, along with others influencing the

source and transport of atmospheric moisture, generate

characteristic δD signatures of water pools recorded by

the photosynthetic organisms (Fig. 12) (Sachse et al.,

2012). Local climatic factors can further alter the δD

signal of water ecosystems (δDlake) through enhanced

evaporation rate or increased river inflow. Therefore,

understanding the factors influencing the δDprecip and

also δDlake is crucial for the accurate interpretation of

the mechanism that drives the n-alkane δD variability.

Fig. 12. Hydrogen isotope fractionation in the water cycle (after Mügler, 2008). Various aquatic and terrestrial plants use

different water pools for biosynthesis tracking the δD variability of source water. A convective system is also illustrated with two

processes contributing to the amount effect and modulating the isotopic composition of water vapor (after Risi et al., 2008).

14

Fig. 13. Processes affecting the n-alkane δD values (adopted

and modified from Aichner, 2009 and Mügler, 2008).

δD composition of n-alkanes

The hydrogen isotopic composition of individual n–

alkanes has become an established proxy for palaeo-

hydrological research (e.g. Eglinton and Eglinton, 2008;

Aichner et al., 2015). Photosynthetic organisms use

their ambient water as their primary source of hydrogen

to synthesize organic compounds such as lipids (n-

alkanes). Therefore, the n-alkane δD values track, in

principle, the δD variability of source water modulated

by climate factors as discussed above (Fig. 12) (Sachse

et al., 2006; Garcin et al., 2012; Sessions, 2016).

However, there is a mean offset of ca -130‰ to -160‰

between source water and lipids, attributed to bio-

chemical isotopic fractionations during biosynthesis of

n-alkanes (Fig. 13) (Sessions et al., 1999; Sachse et al.,

2004). In addition, this signal can be altered by isotopic

fractionations occurring during evaporation of lake, soil

water evaporation and leaf-water transpiration (Fig. 13).

The δD values of short and middle chain n-alkanes

produced by aquatic organisms have been shown to

correlate with lake-water δD, modulated by the balance

between freshwater input and evaporation in close

ecosystems (Huang et al., 2004; Mügler et al., 2008;

Guenther et al., 2013). Lower δD values are expected

by the enhanced input of D-depleted precipitation and

river flows, while strong evaporation can cause

significant D-enrichment of lake water relative to

precipitation. Analogously, the δD values of the

terrigenous long-chain homologues (C27-C31) have been

shown to reflect the isotopic signature of δDprec linked

to climate parameters (Daansgaard, 1964; Huang et al.,

2004; Sachse et al., 2004, 2012 and references therein).

The offset between the δD values of terrestrial and

aquatic lipids (Dterr-Daq) has been proposed as a

proxy for reconstructing terrestrial evapotranspiration

and palaeo-hydrological conditions in lakes (Sachse et

al., 2004; Mügler et al., 2008). In addition to δDprec and

biosynthetic fractionation, δD values of terrestrial n-

alkanes are affected by soil water evaporation and leaf-

water transpiration (Fig. 13) (Smith and Freeman, 2006;

Kahmen et al., 2013). This results in an isotopic

difference between aquatic and terrestrial n-alkanes

which is mainly dependent on hydroclimatic conditions

(Mügler et al., 2008; Duan et al., 2011). In humid

climates with positive water balances, aquatic n-alkanes

have been shown to have more negative δD values

because they are not affected by evapotranspirative

enrichment in contrast to terrestrial n-alkanes which

show more enriched δD values. In more arid climates,

additional isotopic enrichment of the lake water will

lead to the enrichment of aquatic n-alkanes compared to

the precipitation source. However, the D-enrichment in

leaf water recorded in the δD values can be quite

variable (from 18% and 100%) depending on climate

conditions and leaf physiology (Kahmen et al., 2013).

Because of these confounding effects, the aquatic-

terrestrial offset approach needs to be used with care.

Variations in the δD values of n‐alkanes are not

only caused by changes in the δDprecip itself, but are also

influenced by several environmental factors such as

salinity and vegetation changes (Liu et al., 2006; Duan

and He, 2011; Yang et al., 2011; Aichner et al., 2017).

In particular, isotopic fractionation has been shown to

increase in some aquatic plant n-alkanes under high

salinity potentially negating the water isotope signal

(Ladd and Sachs, 2012; Aichner et al., 2017; He et al.,

2017). This can lead to an inverse relationship between

salinity and n-alkane δD values (higher salinity, lower

δD values). Moreover, the effects of vegetation changes

on n-alkane δD values are largely attributed to different

plant physiology and biochemistry (e.g. biosynthetic

fractionation). In particular, apparent fractionation

between source water and lipids for individual species

has been shown to range from −204‰ to −34‰

resulting in different δD values (Sachse et al., 2102). In

addition, the δD values of leaf waxes has been shown to

differ by as much as 70‰ for various growth forms,

with trees and ferns having the highest values compared

to grasses (Hou et al., 2007). This δD variability

between different forms has further been attributed to

various groundwater sources used by the associated

organisms and the effects of micro-climate around the

tree and grasses leading to different degrees of evapo-

transpiration (Hou et al., 2007; Sachse et al., 2012).

Therefore, the use of n-alkane δD values for paleo-

climate reconstruction is based on two assumptions: 1)

These values are correlated to the source water δD

values, and 2) modulation of the primary climate signal

by vegetation change is limited or well-constrained

(Sachse et al., 2012). If these two pieces of information

are not available then a complementary multiproxy

analysis can help with more accurate δD interpretation.

δ13C and δD analysis of n-alkanes

The stable δ13C and δD isotopic compositions of n-

alkanes were measured on a Thermo Finnigan Delta V

gas chromatograph-isotope ratio mass spectrometer

(GC-IRMS) coupled to a ThermoTrace GC 2000 with a

ConFlo IV and GC-isolink system. For the δ13C

analysis, the GC oven temperature was programmed to

start at 100°C increasing with a rate of 20°C/min to

250°C followed by a rate of 5°C/min until 340°C,

15

where it was held stationary for 18 mins. For the δD

analysis, the GC oven program was set to: 100 to 250°C

at a ramp of 15°C/min, and then another ramp of

10°C/min until 320°C, which remained for 9 mins. Two

μl of the sample were injected into the GC and helium

was used as a carrier gas at a constant rate. The

compounds were separated on a Zebron ZB-5HT

Inferno GC column. A standard mixture of n-alkanes

with known isotopic compositions (reference mixture

A6, provided by Arndt Schimmelmann, Indiana

University, USA) was analyzed several times daily to

check instrument performance and to calibrate the

reference gas pulses (CO2 and H2) against which the

isotope compositions were measured. The H3+ factor

was determined on a daily basis and typically accounted

for 3.4-3.5 ppm mv-1. The standard deviation of the

samples for the δ13C and δD analyses was <1 and <5

‰, respectively. Duplicates for δ13C and triplicates for

δD were measured. The isotopic values were calculated

with ISODAT software and are reported as mean values

(against VPDB for δ13C and against VSMOW for δD).

Bulk geochemical analysis

The bulk geochemical properties studied in this thesis

included the total organic carbon (TOC) content, the

carbon to nitrogen ratio (C/N) and the stable carbon

isotope composition (δ13C). TOC measurements were

performed to quantify the amount of OM contained in

sediments. C/N ratio was applied in the Agios Floros

core to distinguish between algal and land-plant origins

of sedimentary OM. Protein-rich algae are relatively

enriched in nitrogen (N) and thus tend to have C/N

ratios of <10 whereas cellulose-rich and protein-poor

vascular plants has C/N ratio of >20 (Meyers and

Teranes, 2001). Intermediate C/N values indicate OM

dominated by macrophytes, or a combination of

terrestrial plants and macrophytes (Kendall et al.,

2001). Bulk δ13C composition has previously been used

to distinguish potentially sources of sedimentary OM

(e.g. C3 versus C4 plants, marine versus freshwater

algae and macrophytes versus phytoplankton) (Meyers,

1994). The bulk isotope approach, however, can be

problematic for two reasons. First, bulk isotope values

potentially record inputs of carbon from terrestrial and

aquatic plants making the distinction between different

sources dubious (Tanner et al., 2010). For instance,

phytoplankton (C3 algae) use dissolved CO2 which is

usually in equilibrium with the atmosphere and is

therefore isotopically indistinguishable from organic

matter produced by C3 plants in the surrounding

catchment (Meyers and Teranes, 2001; Sifeddine et al.,

2004). Secondly, diagenetic effects on isotopic values

are not well constrained, which can further complicate

the interpretations of records (Tanner et al., 2010).

In this study, the bulk geochemical data were used

as a complementary approach to the main proxy

analysis. Sediment samples (resolution of 10 cm for the

Agios Floros core, and 5 cm for the Gialova and Lerna

cores) were freeze-dried and powdered with porcelain

mortar. Aliquots of the samples were weighed and

wrapped into tin capsules. The TOC amount was

measured on samples decarbonated with HCl (10%) and

dried overnight. For isotope analysis, the samples were

combusted with a Carlo Erba NC2500 analyser

connected via a split interface to reduce the gas volume

to a Finnigan MAT Delta V mass spectrometer. The

reproducibility was calculated to be better than 0.15‰

The TOC amount and the total nitrogen (TN) values

were determined when measuring the isotope ratios.

The relative error was <1% for both measurements.

6.2.4. XRF core scanning

X-ray fluorescence (XRF) core scanning has become a

standard analytical technique for non-destructive and

rapid analysis of sediment cores at sub-millimeter

scales (Croudace et al., 2006; Francus et al., 2009). The

Itrax core scanner produces high-resolution elemental

profiles and optical and X-radiographic images of

cores. The scanner measures the elemental composition

as element intensities in total counts second-1 (cps). The

measurements reflect the relative concentration of each

element. Variations in elemental composition can be

connected to various processes within lakes and in

catchments including shifts in minerogenic input, water

level changes and redox processes (e.g. Moreno et al.,

2007; Kylander et al., 2011). The XRF technique has

successfully been applied in lacustrine and marine

sediments for studying paleoenvironmental changes

(Francus et al., 2009; Croudace and Rothwell, 2010).

In the present study, XRF scanning analysis was

performed on subsamples taken throughout the Gialova

core to complement the biomarker results. Few samples

were also analyzed from the lower part of Agios Floros

core. All the samples were placed in cubes and scanned

at the SLAM Lab at the Department of Geological

Sciences, Stockholm University using an ITRAX XRF

Core Scanner from Cox Analytical Systems

(Gothenburg, Sweden; Croudace et al., 2006). The XRF

scanner was equipped with a Molybdenum tube set at

30 KV and 45 mA. The analysis was performed with a

step size of 300 mm and integration time of 60 sec per

measurement. Approximately five measurements were

made on each cube surface and an average of these

measurements was calculated to acquire one value for

each sample. The elemental data were normalized by

incoherent and coherent scattering to remove effects of

changes in the water content, density of the sediments

during analysis and by several instrumental parameters

(e.g. dead time tube aging) (Kylander et al., 2011).

Data interpretation for the Gialova samples was

aided by performing principal component analysis

(PCA). The PCA is a useful tool for understanding the

co-variation between variables and identifying patterns

of correlations within the data sets. In particular, PCA

identifies those elements that show the same variability

and are thus likely controlled by the same processes.

PCA calculations were performed using JMP Pro 12

software in correlation mode with a Varimax rotation.

16

7. Results

The results of this thesis are presented as a summary of

five papers. Paper I provides diatom-based evidence

for tectonic- and climate-induced hydrological changes

in the central Messenian plain over the last ca 6000

years. Paper II presents a detailed morphological study

of the diatom species, Cyclotella distinguenda with a

description of a new fossil diatom species, Cyclotella

paradistinguenda from the Agios Floros sequence in

relation to other Cyclotella taxa. Paper III investigates

further the hydroclimate changes in Agios Floros based

on the δD values of aquatic plant‐derived n‐C23 alkanes

(δD23). Paper IV presents a reconstruction of the

Eastern Mediterranean hydro-climate during the last

3600 year mainly based on n-alkanes, their δ13C and δD

values and XRF data in a sediment core from the

Gialova Lagoon. Paper V presents an n-alkane δD

record from the Lake Lerna NE Peloponnese covering

the last 5000 years. This record is compared with other

n-alkane δD studies from SW Peloponnese providing

evidence for changes in the E-W climate gradient over

the peninsula during the last 5000 years. These changes

are linked to shifts in the high-latitude atmospheric

patterns and the effects of the African/Asian monsoons.

7.1. Paper I

Katrantsiotis, C., Norström, E., Holmgren, K., Risberg,

J., Skelton, A., 2015. High-resolution environmental

reconstruction in SW Peloponnese Greece covering the

last c. 6000 years: Evidence from Agios-Floros fen. The

Holocene 26, 188–204.

https://doi.org/10.1177/0959683615596838

This paper presents a stratigraphic investigation of a 7.5

sediment core retrieved from the Agios Floros fen, in

the central-eastern Messenian plain, SW Peloponnese.

The sequence was analyzed for lithostratigraphy,

diatoms and bulk geochemistry (δ13C, TOC, C/N)

complemented with XRF data obtained from selected

subsamples at the bottom of the sequence. The aim of

this research was to reconstruct the hydrological shifts

in the Agios Floros paleolake over the last 6000 years

and to elucidate the driving mechanisms behind these

changes. Special focus was placed to the study of fossil

diatom flora as diatom records from Greece are rare,

due to the alkaline (carbonate) environment that hamper

their preservation. Therefore, the Agios Floros study

provides the first diatom record from the Peloponnese

and further offers the opportunity to improve the

knowledge on the Holocene diatom taxa from Greece.

The Agios Floros sequence covers the last ca 6000

years on the basis of 18 radiocarbon dates. High

accumulation rates (up to 23 mm/yr) are recorded

between two decadal-long periods centered at ca 5700

and ca 5300 cal BP. The sequence consists of fen peat

in the uppermost section. This is underlain by lacustrine

sediments, punctuated by two layers of clay with

diatomaceous silty bands. The diatom assemblage is

dominated by freshwater and indifferent salt-tolerant

taxa which thrive in alkaline (pH>7) waters. In terms of

habitat preferences, there are distinct stratigraphic

changes between sub-aerophilous, benthic and

planktonic taxa. This implies that water level changes

have played an important role in the development of the

Agios Floros basin over the last 6000 years.

Cyclotella distinguenda is the dominant planktonic

species which mainly occurs in the laminated sequence

(Fig. 14). It is also observed with lower amounts in the

organic-rich sediments where diatom valves are highly

dissolved. Cyclotella distinguenda exhibits large

morphological variability throughout the sequence. This

has resulted in the identification of a new species

described in the paper II. Cyclotella distinguenda

indicates the development of lake stages in the Agios

Floros basin with maximum water depth and extension.

Cocconeis placentula occurs in the gyttja with a

wide range of variation in length, width and shape.

Several varieties of this species (var. placentula, var.

euglypta and var. lineata) are encountered (Fig. 14).

Denticula kuetzingii exhibits high abundances in the

laminated clay and in the gyttja. This taxon is observed

as single, linear to elliptical valves and in chains with

valve faces abutting. The most prominent morpho-

characteritic is the fibulae extended to the distal margin

of the valves, forming partitions (Fig. 14). In terms of

ecology, Cocconeis placentula and Denticula kuetzingii

are here classified as benthic. The latter has a wider

range of ecology, which is also evident from its co-

occurrence with Cyclotella distinguenda and Cocconeis

placentula. Denticula kuetzingii can grow in shallow,

relatively deep and open water with high electrolyte

content and nitrate concentrations (Huntsman-Mapila et

al., 2006; Matlala et al., 2008; Mackay et al., 2012).

Ellerbeckia arenaria is abundant in the organic-rich

sediments, mainly underneath peat. Valves of this

species are usually highly fragmented and/ or dissolved

with outer parts missing (Fig. 14). Ellerbeckia arenaria

shows distinct stratigraphic changes, and therefore is

classified as subaerophilous species to separate it from

the common benthic taxa such as Cocconeis placentula.

The Agios Floros sequence contains a number of

benthic species that occur with lower abundances. For

instance, Gomphonema angustatum, Cymbella affinis,

Achnanthes ploenensis var. gessneri and some Eunotia

species are present in the organic sections with <5%.

In summary, there is a clear stratigraphic change

between four main species in response to water level

changes during the last 6000 years. Shifts in the diatom

assemblage are further accompanied by changes in the

amount of phytoliths and the diatom preservation. In

general, valves are well-preserved and the phytolith

amount is high during periods of higher water level and

increased accumulation rates. These shifts are also

accompanied by changes in the geochemical proxies.

Negative excursions in the TOC amount, δ13Corg values,

as well as in the C/N ratio generally correspond to more

positive peaks in the planktonic taxon and vice versa.

17

The Agios Floros diatom and geochemical data

offer a new insight into the paleoenvironmental

evolution of a region where a few high resolution

records are available. The results suggest that the Agios

Floros basin underwent fluctuations from marshy to

deep and open water environments during the last 6000

years (Fig. 15). These changes can be attributed to a

combination of tectonic, climatic and human factors.

At ca 6000-5800 cal BP, the basin was occupied by

a shallow water body with low oxygen/anoxic

conditions. This is evident from the absence of diatoms,

and the presence of a coherent sandy clay layer with

high peaks in Fe and S. Between ca 5700-4600 cal BP,

there is evidence for rapid water level changes in the

Agios Floros basin. Two decade-long periods of a rapid

development of deep lake conditions with an open

water environment were identified at ca 5700 cal BP

and ca 5300 cal BP. These two periods correspond to

diatomaceous laminated clay dominated by Cyclotella

distinguenda, and high accumulation rates. The lakes

likely had a depth of ≤10 m based on the ecological

optima of Cyclotella distinguenda from other

Mediterranean studies and the Alpine training set

(Wunsam et al., 1995; Currás et al., 2012). These events

can be connected to local tectonic processes, and

particularly, to a two-stage deepening of the basin in

response to earthquakes along the western flank of the

fault-bounded Taygetos Mountain. Using empirical

relationships, the possible moment magnitude of these

earthquakes was estimated to be MW=6.7 causing a

vertical displacement of 1 m for each event. An

increase in the flow rate of springs associated with

seismic stress in bedrock should also have contributed

to high water levels before, during and/or after these

events. Moreover, high amount of Denticula kuetzingii

likely indicates changes in the lake chemistry, related to

increased electrolyte content and nitrate concentrations

in the water discharging from the karst aquifers.

Apart from these tectonic processes, abrupt climatic

changes with enhanced precipitation might have played

a role as this was a period of increased humidity in the

eastern Mediterranean region. The two deep water

phases were terminated at ca 5650 and ca 5280 cal BP,

probably due to high accumulation rates. Thereafter,

another two events of shallow to intermediate lake

levels were identified at ca 5200 and ca 4600 cal BP.

After ca 4500 cal BP, the development of peat and

the disappearance of diatoms can be attributed to both

human and climate factors. This period in the Agios

Floros area is associated with enhanced human

activities (Simpson, 2014), which likely caused

shallowing of the basin initiating vegetation succession.

At the same time, a shift to drier conditions is also

evident from other regional records (e.g. Finné et al.,

2017). After ca 2800 cal BP, the appearance of highly

fragmented valves infers a return to wetter conditions as

a response to marked rainfall seasonality, flooding

events and/or human activities. These conditions led to

the development of the present-day environment with

cultivated lands and seasonally semi-flooded fields.

Fig. 14. SEM photos of diatom species found in the Agios Floros sequence: (a) Cyclotella distinguenda, (b) Cocconeis

placentula, (c) Denticula kuetzingii, (d) Ellerbeckia arenaria, (e) Cymbella affinis, (f) Achnanthes ploenensis var. gessneri

(right) and Eunotia species (left).

b c a

d e f

18

7.2. Paper II

Katrantsiotis, C., Risberg. J., Norström, E., Holmgren,

K., 2016. Morphological study of Cyclotella

distinguenda and a description of a new fossil species

Cyclotella paradistinguenda sp. nov. from the Agios

Floros fen, SW Peloponnese, Greece in relation to other

Cyclotella species. Diatom Research 31, 243–267.

https://doi.org/10.1080/0269249X.2016.1211178

This study was initiated by the results of the previous

paleoenvironmental research from the Agios Floros fen.

In particular, during the analysis of the diatom

succession, large amounts of two types of Cyclotella

cells were encountered with specific stratigraphical

distribution in the Agios Floros core. These cells were

generally characterized by similar valve ornamentation

but had distinct size and structure of central areas and

stria densities. Based on routine microscopical

observations and the existing literature, they were

tentatively classified as two different morphotypes

within Cyclotella distinguenda. The need for more

detailed investigation emerged from the uncertainties

associated with casual microscopical observations and

the absence of recent studies on this species. In this

study, a closer investigation of these cells was carried

out following detailed LM and SEM observations on a

large number of valves. Morphological observations

were combined with a simple statistical approach.

The results show that there are constant and distinct

differences in the morphology and ultrastructure

between the two morphotypes. These differences, along

with their distinct stratigraphic distribution, provide

sufficient evidence to recognize a new species. On this

base, one morphotype is here described as a new taxon,

Cyclotella paradistinguenda. The other morphotype is

assigned to Cyclotella distinguenda and is further

consistent with the original description of this taxon.

The two species can be distinguished by a combination

of distinct differences in the structure and size of central

Fig. 15. The development of the Agios Floros fen during the last 6000 years. Water in bedrock is under artesian conditions flowing through fractures and discharging as flowing artesian springs. Seismic stress at 5300 and 5700 ca BP likely caused

high flow rate of the springs further contributed to deep water conditions.

19

areas, the structure and number of striae, the

arrangement of marginal fultoportulae/density of costae

between fultoportulae, the shape of alveolar chambers

and rimoportulae (Fig. 16). The two species also have

in common, striation of almost equal length, central

area lacking fultoportulae and a single rimoportula

situated on a costa within the ring of marginal

fultoportulae. Based on these similarities, the Cyclotella

distinguenda complex species is further proposed as a

new morphological group which includes the closely-

related taxa Cyclotella distinguenda and its varieties,

Cyclotella paradistinguenda and Cyclotella plitvicensis.

Cyclotella paradistinguenda is only known from

Agios Floros, and thus its ecological interpretation can

be inferred from its co-occurrence with other taxa of

known ecology and lithostratigraphic changes.

Cyclotella paradistinguenda occurs underneath peat,

where the diatom abundance is low and is mainly

dominated by dissolved valves of the subaerophilous

species, Ellerbeckia arenaria. Therefore, it can be

concluded that Cyclotella paradistinguenda is tolerant

of shallower conditions with lower nutrient availability

and/or higher pH compared to Cyclotella distinguenda.

This research could be used as a guide for relevant

diatom studies in the Mediterranean region helping out

with the identification and ecological classification of

Cyclotella species. High taxonomical resolution and

ecological separation of closely-related species are also

essential to improve environmental monitoring and

produce accurate paleolimnological reconstructions.

7.3. Paper III

Norström, E., Katrantsiotis, C, Finné, M., Risberg, J.,

Smittenberg, R., Bjursäter, S., 2018. Biomarker

hydrogen isotope composition (δD) as proxy for

Holocene hydro-climatic change and seismic activity in

SW Peloponnese, Greece. Journal of Quaternary

Science 33, 563–574.

https://doi.org/10.1002/jqs.3036

This paper is mainly based on the analysis of the n-

alkane distributions and δD composition of aquatic

plant-derived n-C23 alkanes (δD23) in the Agios Floros

core. The goal is to complement our previous diatom-

based study and to fill gaps in the record where diatoms

are absent. This multiproxy method establishes a

continuous, hydro-climate record for the last 6000

years, integrated with other paleoclimate data from the

Peloponnese and the Eastern Mediterranean. Another

aim is to validate the n-alkane δD application for this

particular environment by comparing the outcome of

the present research with our previous diatom-based

study. This further offers the opportunity to test and re-

evaluate the water-level changes at 6000-4500 cal BP.

The carbon isotope composition of n-C23 alkane

(δ13C23) shows more stable values than δ13C of long

chain n-alkanes, mainly after 4500 cal BP. This

indicates a stable source for n-C23 suggesting that any

substantial effects of vegetation changes have a minor

impact on the δD23 signal. Thus, the observed

Fig. 16. (a-d) Cyclotella paradistinguenda. (a-b) External valve view and (c-d) Internal valve view. (e-f) Cyclotella

distinguenda. (e) External valve view and (f) Internal valve view. The arrows show the position of marginal fultoportulae

and the circles indicate the position of marginal rimoportulae.

a b e

f d c

20

variability of the δD23 profile is attributed to changes in

source water δD, modulated by the isotope signal in

precipitation and evaporative effects on the fen water. The δD23 signal and the n-alkane distribution support

the paleolimnic conditions inferred by the diatom data,

with maximum aquatic biomarker abundance at ca 5300

and ca 4600 cal BP (Fig. 17). The deep lake at ca 5700

cal BP is reflected by a slight increase in the aquatic n-

alkane abundance, likely due to low organic content in

this part of the core. Shifts in δD23 at ca 5700 and ca

5300 cal BP are abrupt and short-lived. They also

correspond to distinct changes in the diatom

composition dominated by Cyclotella distinguenda

(Fig. 17) as well as to high accumulation rates. It is thus

proposed that the δD23 anomalies are caused by tectonic

events that led to temporal mixing of groundwater from

different aquifer systems, thereby altering the isotope

signal of the fen water during annual to multi-annual

periods. The δD23 signal at ca 4600 cal BP corresponds

to lower accumulation rates, organic-rich sediments and

the dominance of tychoplanktonic/benthic species. A

short-lived drop in δD23 is also evident at ca 2800 cal

BP. Similar hydrological changes at ca 4600 and ca

2800 cal BP are also observed at other sites in the

Peloponnese and beyond. This suggests that these two

events are likely attributed to large-scale climate shifts.

From a long-term perspective, the Agios Floros

δD23 record indicates wetter conditions between ca

6000-4500 cal BP, followed by an aridification trend

until ca 2900 cal BP, in agreement with other eastern

Mediterranean records. Thereafter, the δD23 signal

indicates a return to humid conditions followed by a

period of enhanced aridity and stronger seasonality

contrasts from 2000-1500 cal BP until modern times.

The present study confirms the ability of n-alkane

δD approach to reconstruct climate changes in this

particular environmental setting. The combined use of

n-alkane δD approach with other proxies is also

promising for the identification of past seismic events.

7.4. Paper IV

Katrantsiotis, C., Kylander, M., Smittenberg, R.H.,

Yamoah, K.K.A., Hättestrand, M., Avramidis, P.,

Strandberg, N.A., Norström, E., 2018. Eastern

Mediterranean hydroclimate reconstruction over the last

3600 years based on sedimentary n-alkanes, their

carbon and hydrogen isotope composition and XRF

data from the Gialova Lagoon, SW Greece. Quaternary

Science Reviews 194, 77–93.

https://doi.org/10.1016/j.quascirev.2018.07.008

This paper presents a 3600-year multiproxy geo-

chemical record of climatic changes from the Gialova

Lagoon, SW Peloponnese. The analysis is based on a

2.6 m radiocarbon-dated sediment core retrieved from

the central part of the lagoon. The dataset consists of n-

alkane distribution, their δ13C and δD values, bulk

organic geochemistry and a XRF core scanning profile.

This approach was complemented with a semi-

quantitative analysis of plant remains. The goal of this

study is to trace the sources of sedimentary OM in the

Gialova Lagoon and to extract paleo-climate data over

the last 3600 years. Another goal is to produce a climate

reconstruction for the Eastern Mediterranean by

comparing the Gialova data with other regional records,

and to explore the drivers behind the observed changes.

The results show that the sedimentary OM has

largely been derived from the local aquatic vegetation.

High TOC content coincides with high abundances of

macrophyte remains, mainly seeds from Ruppia

maritima, and a long-term trend towards positive δ13C

values of aquatic plant-derived mid-chain n-C23-C25

alkanes. These high δ13C23-δ13C25 values (up to -19‰)

can mainly be attributed to carbon-limiting conditions

during periods of aquatic vegetation expansion, causing

plants to assimilate isotopically-enriched HCO3−. The

δ13C23-δ13C25 profiles co-vary with the δ13C signals of

the long-chain n-alkanes, and especially with the

δ13C27-δ13C29 records, which exhibit values of up to –20

and –22‰, respectively. It is likely that the n-C27-C29

alkanes consist of different degrees of mixing between

aquatic and terrestrial plants triggering shifts towards

positive δ13C27- δ13C29values due to the HCO3− effect.

The δ13C record of algae-bacteria derived n-C17

alkane is stable throughout the sequence indicating a

stable source organism (not shifting between dissolved

CO2 and HCO3−). The δD17 profile co-varies with δD of

all n-alkanes (δD23-31) implying that they all reflect

changes in the source water isotope composition, driven

by hydroclimate variability. In addition, the n-C31

alkane shows lower δ13C variability compared to n-C27-

C29 alkanes whereas the δD signal of the same n-alkane

exhibits the widest isotopic range in the record with an

average value of ca -190‰. This value is more negative

by ca 20‰ compared to that of aquatic-derived alkanes

indicating that the δDprec-driven δD31 signal is further

enhanced by the additive effect of evapotranspiration.

Principle Component Analysis (PCA) of the XRF

data indicates shifts between dry and wet conditions.

PC1 explains 53% of the observed variance. K, Al, Rb,

Fe, Ti and Si associated with clastic sediments load

positively on PC1. These elements can be transported

by floods and rivers during wet periods. Ca and Sr

driven by carbonate precipitation during dry periods

load negatively on PC1. The δD17-δD31 signals

generally covary with PC1 (Fig. 17). This suggests that

both proxies are driven by a common climate signal.

Over longer time-scales, the δ13C23-δ13C29 records

are generally anti-correlated with the n-alkane δD

(δD17-31) profiles and the PC1 axis. This indicates that

shifts in the expansion of aquatic vegetation are related

to climatic variability. Overall, macrophyte-dominated

periods correspond to wet and/or cold episodes during

which low salinity and higher water level likely created

favorable conditions for plant growth in this lagoon.

The records provide evidence for shifts from dry

(warm) periods at ca 3600-3000, ca 1700-1300 and

900-700 cal BP (late Medieval Climate Anomaly) to

wet (cold) episodes at ca 3000-2700, ca 1300-

21

-900 (early Medieval Climate Anomaly) and ca 700-

200 cal BP (Little Ice Age). This climatic fluctuation

can be explained by the relative dominance of high-

latitude and low-latitude atmospheric patterns over SW

Peloponnese. The Gialova record between 3600 and

2000 cal BP and during the LIA resembles other

central-western Mediterranean records. This suggests

that the NAO exerted the main control in SW

Peloponnese during these periods. Conversely, the

climatic signal from 2000 to 900 cal BP appears

synchronous with Anatolian records, indicating that

other regional atmospheric patterns such as the NCP

had the dominant influence for this time-interval. In

addition, the climate variability revealed in the Gialova

record is almost synchronous with shifts in the intensity

of East African-Asian monsoons; drier (wetter)

conditions in Gialova are associated with periods of

enhanced (weak) monsoons. This can primarily be

attributed to the more northward (southward) position

of the Intertropical Convergence Zone (ITCZ) and the

associated Subtropical High. The large-scale

teleconnection with Asian monsoons would also result

in stronger subsidence and more intense Etesians,

which act as katabatic winds in the western

Peloponnese, further enhancing the summer warming.

Overall, the results from the present study and their

comparison with other paleoclimatic records from the

Mediterranean and beyond improve our knowledge of

the late Holocene regional climate evolution, and the

related drivers. The present study also sheds light on the

sources of OM in this coastal environment, and the

factors that influence its distribution. This is crucial for

more accurate quantification of regional and global

carbon budget and for forecasting changes in the carbon

cycling induced by climatic and anthropogenic impacts.

7.5. Paper V

Katrantsiotis, C., Norström, E., Smittenberg, R.H.,

Finne M., Weiberg E., Hättestrand, M., Pavlos

Avramidis Wastegård, S., 2019. Climate changes in the

Eastern Mediterranean over the last 5000 years and

their links to the high-latitude atmospheric patterns and

Asian monsoons. Global and Planetary Change 175,

36–51. https://doi.org/10.1016/j.gloplacha.2019.02.001

This paper presents a 5000 year record of n-alkane

distributions and their δD compositions as well as bulk

organic geochemistry (δ13C, TOC) from the ancient

Lake Lerna in NE Peloponnese. The specific goals are

to extract paleoclimate data from the Lerna core, and

also to compare these data with other n-alkane δD

records from SW Peloponnese. Through this

comparison, shifts in the W-E rainfall/temperature

gradient over the Peloponnese peninsula are examined

during the last 5000 years. Another goal of this study is

to explore the nature of the observed changes, and to

assess linkages between regional climatic variability

and shifts in the large-scale atmospheric patterns.

Fig. 17 Comparisons of XRF and δD31 records from the Gialova Lagoon with δD23 and the abundance of planktonic

/tychoplanktonic species from the Agios Floros fen as well as with the Lake Lerna δD23, ACL and Paq records.

22

The results show that there is an anti-correlation pattern

between the n-alkane abundances of the mid-chain and

long-chain homologues. This indicates two distinct

sources, which is also evident from the more positive

average δD23-25 values than the δD29-31values. The mid-

chain n-alkanes are attributed to aquatic plants

(submerged-floating). The n-C27–C29 alkanes likely

originate from the fen and the n-C31 alkane is mostly

derived from the terrestrial vegetation around the fen.

The n-alkane δD profiles (C23 to C31) covary with

each other indicating that they all reflect changes in the

isotopic composition of source water. The δD records

also covary with Paq, which has been used a proxy for

lake level changes (Fig. 17). High Paq values indicate

increased contribution from aquatic macrophytes and

thus higher water level, which coincides with more

negative δD values and vice versa. This interpretation is

supported by the higher ACL values during periods of

low Paq and positive δD trends. In the Peloponnese,

plants with high drought adaptive capacity have been

shown to produce longer chain n-alkanes (Norström et

al., 2017). This indicates that during dry periods the

sedimentary n-alkanes likely originate from drought-

adapted plants and moisture stressed vegetation.

Despite the general co-variability of the n-alkane

δD records, short-term terrestrial vegetation changes,

known to have taken place in this region, might bias δD

of long chain n-alkanes over shorter timescales.

Therefore, the climate reconstruction is mainly based

on the predominantly macrophyte (submerged

/floating)-derived δD23 which shows the highest long-

term variability in the record compared to δD29-31.

The comparison of the δD records from SW and

NE Peloponnese reveals sometimes similar and

sometimes opposite climate signals between the two

areas. The records infer high humidity in the peninsula

at ca 5000-4600, ca 3000-2600 (more unstable in SW)

and after ca 700 cal BP with drier periods at ca 4100-

3900 and 1000-700 cal BP. On the other hand, a W-E

opposite climate signal is evident at ca 4600-4500, ca

3200, ca 2600-1800 and ca 1200-1000 when the Lerna

signal shows the highest δD values with a reversal at ca

3900-3300, ca 3200-3000 and ca 1800-1300 cal BP.

Concluding, this paper provides evidence for shifts

in the W-E precipitation gradient over the Peloponnese

during the last 5000 years. These changes can be

explained by the relative dominance of high-latitude

atmospheric patterns, and particularly the NAO and the

NCP, over the Peloponnese. In addition, the data from

this paper support our previous outcome that the

African and Asian monsoonal systems have played a

major role in the summer climatic conditions in the

Eastern Mediterranean. Summer temperature changes

are particularly associated with shifts in the intensity of

Asian monsoons. These changes are potentially

superimposed on the precipitation signal reflected in the

δD records. The physical mechanism underlying the

large-scale teleconnections with high latitude and low

latitude atmospheric patterns is further explored in this

paper and the discussion part of the present summary.

8. Discussion

The main goal of this project was to increase the

knowledge of the environmental and climate changes in

the Peloponnese, SW Greece during the middle and late

Holocene (the last ca 6000 years) and to contribute with

new paleoclimate data for the Eastern Mediterranean.

To achieve this, a multiproxy analysis, including

diatoms, n-alkanes and their isotope composition as

well as XRF data, was applied on three sediment cores

from the SW and NE Peloponnese, two areas with

opposite climatic conditions. The results from the

multi-proxy studies include; i) reconstruction of long-

term climatic trends and identification of specific

events, ii) chronological correlation of the sequences

with other records from the Mediterranean and beyond

iii) identification of non-climatic drivers influencing the

landscape development in this region, iv) identification

of sedimentary OM sources in the Gialova Lagoon, and

(v) description and ecological separation of a new fossil

diatom species as well as possibly association between

niche environmental evolution and diversification.

8.1. Chronology and resolution

The analyzed sediment cores are comparatively well-

dated (high number of dates) taking into account the

long time-intervals they cover. The age-depth models

are based on dates derived from seeds of emergent and

terrestrial plants as well as of floating plants that utilize

atmospheric carbon. Some bulk sediments were also

dated in the Agios Floros and Lerna cores. In the

Peloponnese, further uncertainties are introduced when

performing 14C dating on bulk samples or aquatic plant

remains since the bedrock is made up of limestones and

will contribute with old carbon to the sediments.

Aquatic plants will, during photosynthesis, take up this

old carbon resulting in considerably older radiocarbon

dates (Olsson, 1991). In addition, bulk sediments can

contain a mixture of components with widely differing

dates, related to hard water effect or inwash of old

detrital OM from the catchment. Despite these

uncertainties, the dates from the Gialova and Lerna sites

appear in stratigraphic order. In addition, the Agios

Floros age-depth model is robust, mainly above 200

cm, with some outliers between 200 and 400 cm.

The resolution is also an important factor when

comparing records with uneven temporal spacing of the

samples resulting from variations in accumulation rates

(Rehfeld and Kurths, 2014). In this study, the sampling

was carried out at a resolution of ca 5 cm. For Agios

Floros δD23, the sampling was performed at every ca 10

cm. Hence, the resolution is low during periods of low

accumulation rates, which holds especially true for the

Agios Floros δD23 and Gialova records. This irregular

sampling in time hampers the identification of short-

term events in SW Peloponnese. In the Lerna study,

continuous accumulation rates as indicated by the age-

depth model and also the gradual boundaries between

layers resulted in a relatively high resolution record.

23

The dating and resolution issues are described

below highlighting the periods of low resolution data. (i) The Agios Floros diatom record has an average

temporal resolution of ca 52 years per sample. The

highest resolution (ca 8-10 years) is observed below

350 cm (before ca 5100 cal BP) (Fig. 17). The

resolution above this depth ranges from 40 and 90

years. The δD23 record has an average resolution of ca

125 years per sample, with the lowest resolution (ca

230 years) above 50 cm (after 2500 cal BP). The age-

depth model is based on 15 dates with an average

dating uncertainty of ±63 years (min±18, max±160).

There is a general overlap in the 2σ confidence intervals

below 200 cm while five dates were excluded as they

show reversals. These dates were obtained from seeds

of Cladium mariscus (emergent plant) and bulk

sediments and correspond to periods of abrupt water

level changes. Thus, the reversals could be related to

incorporation of aquatic carbon by the emergent

vegetation or reworked material. Nevertheless, some of

the dates (689, 366-374, and mainly 338 cm) were

based on terrestrial seeds and appear in a stratigraphic

order. This indicates that despite some uncertainties,

our core chronology should be considered reliable. In

addition, the comparative dating on terrestrial seeds and

bulk sediments above 200 cm indicates that there is no

age difference, and bulk material can be considered

suitable for age determination within the peat section. (ii) The Gialova record has an average resolution of 71

years per sample ranging from ca 100-160 years per

sample at the depth of 150-90 cm (2600-800 cal BP) to

ca 20-70 years per samples in the rest of the sequence.

The age-depth model is based on seven dates with an

average uncertainty of ±50 years (min ±35, max ±88).

The dates were mainly obtained from seeds of the

rooted-floating or free-floating plant, Najas, which

takes up CO2 from the atmosphere (Prasad et al., 1997).

Two dates are based on charcoal and terrestrial seeds

respectively, and they all appear in stratigraphic order

which strengthens the core chronology. Dates obtained

from seeds of the aquatic plant, Ruppia maritima show

a deviation of ca 100 years from the model interpreted

as an indication of a minor potential reservoir effect. (iii) The Lerna record has an average temporal

resolution of 48 years/sample. This is the highest

achieved resolution for isotope/microfossil-based study

of a sediment core in the Peloponnese. The age-depth

model was constructed using seven dates from seeds of

emergent plants and bulk sediments. The average dating

uncertainty is ±68 years (min±25, max±91) after

calibration. The dates appear in stratigraphic order,

although two of them (one bulk sample and one sample

with a charred appearance) showed reversals and were

excluded from the model. The reversed date from the

bulk sample at 222 cm corresponds to a clay layer

which is barren of plant remains. This indicates that

even low contamination levels from old carbon could

have larger effects on this date compared to the dates

related to organic-rich accumulations (Olsson, 1991).

8.2 Proxy data

Multiproxy records obtained from the same studied

sites can provide both complimentary and comparative

information. This approach aims to identify possible

effects of confounding variables (i.e. local, non-

climatic factors). However, different proxies can be

influenced by various environmental factors at a range

of spatial scales, and therefore show different strengths

and weaknesses (Birks and Birks, 2006). In this study,

special attention is given to the diatom preservation and

how this affects the interpretation, the ecology of new

diatom species as well as the origin of n-alkanes that

can influence the δD interpretation. The causes behind

the variability of proxy records are also discussed, and

particularly whether these changes are associated with

regional climate shifts or local environmental factors.

8.2.1. Diatom preservation

The availability of modern diatom data in Greece is

limited due to the scarcity of relevant studies and the

lack of long-term ecological monitoring dataset (Ziller

and Montesanto, 2004; Solak and Àcs, 2011). In

addition, diatom-based paleo-environmental studies in

the central-eastern Mediterranean, and especially in

Greece, are relatively rare (Wilson et al., 2008;

Cvetkoska et al., 2014). In addition, there are no

previous diatom studies in the Peloponnese. This can be

attributed to unfavorable conditions for diatom growth

and preservation due to the carbonate bedrock and/or

low silica availability. Therefore, the limited regional

diatom database and the variable degree of valve

preservation in sediments potentially lead to some

uncertainties regarding the interpretation of changes in

the composition of fossil flora in the present study.

The Agios Floros diatom record shows profound

changes in the dominant species abundances indicating

lake level shifts in this small tectonic basin over the last

ca 6000 years. Overall, the Agios Floros study provides

a unique diatom record from the Peloponnse, which is

also evident from the absence of diatoms in the Gialova

and Lerna cores. However, valve preservation in the

Agios Floros core is poor to moderate. High amount of

dissolved valves, including dissolved fragments, mainly

occurs in the organic-rich accumulations (gyttja and

peat) compared to the diatom-rich clay (Fig. 18).

Poor preservation can be related to both physical

breakage and chemical dissolution prior to and during

the accumulation of valves in sediments. Highly

alkaline conditions can be one factor affecting diatom

preservation in this carbonate system. The comparison

of dissolution index with accumulation rate indicates

that these two factors are related to each other and they

are both associated with the diatom abundance (Fig.

18). High diatom abundance (diatomaceous clay) and

low dissolution index (well-preserved valves) mainly

occur during periods of high accumulation rates. The

latter potentially promotes diatom preservation as the

deposited valves are quickly removed from the

sediment–water interface and uppermost sediment

24

layers where most of dissolution occurs (Flower, 1993;

Flower and Ryves, 2009). However, diatom valves

would still continue to dissolve if pore waters remained

undersaturated with regard to silica (Flower, 1993).

Therefore, high pore-water concentrations of silica

(biogenic silica production is high enough to saturate

pore waters) during periods of high accumulation rates

would prevent sedimented diatom valves from

dissolving. In addition, well-preserved valves occur in

the diatomaceous sequence, which corresponds to deep

water conditions (peaks in planktonic taxa), indicating

the role of limnological conditions in the valve

preservation. Anoxic and calm water environment have

been linked to enhanced valve preservation, as

bioturbation/mixing is being reduced (Flower and

Ryves, 2009). On the other hand, lower water level,

increased turbidity and high energy environments can

affect the quality of valves through physical breakage

which in turn can speed up the dissolution rate (Flower,

1993; Reed, 1998; Ryves et al., 2006). Other factors,

such as temperature and salinity, might also have

played a role (increased dissolution under high

salinity/temperature; Ryves et al., 2006). However, the

Agios Floros fossil flora does not indicate substantial

changes in salinity. In addition to environmental

factors, valve preservation depends on the size and

degree of silicification of different species (Stoermer

and Smol, 2010). Robust and more silicified species are

more resistant to dissolution and also to physical

breakage compared to finer taxa (Ryves et al., 2006).

The variable valve preservation in the Agios Floros

sequence might affect the representativeness of fossil

assemblage. Large and heavily silicified species (e.g.,

Cyclotella paradistinguenda and Ellerbeckia arenaria)

replace relatively smaller forms (e.g. Cocconeis and

Denticula). This can be associated with changes in the

diatom preservation (Fig. 18). During the transition to

more robust forms (mainly above 350 cm), the overall

preservation seems to deteriorate, and consequently the

more fragile taxa may be underrepresented. This change

in the valve preservation can further be attributed to the

shallowing of the lake (desiccation effect) and/or to

decreased sedimentary burial rates which would cause

valves to remain exposed to water for longer periods.

8.2.2. The new diatom species and its affinity

The Cyclotella genus is the most taxonomically,

ecologically, and morphologically diverse genus of

freshwater planktonic diatoms. This genus contains

more than 300 species, characterized by extensive

polymorphism and biogeographical variability. Several

morphological groups, each consisting of similar taxa,

have been divided within the Cyclotella genus. Species-

specific character variability has been linked to life-

cycle variation, environmental conditions and genetic

differentiation (Mann, 1999; Kociolek and Stoermer,

2010). The average cell size of a population of centric

species decreases during its life cycle as vegetative cell

division leads to the production of daughter valves

which are smaller than the parent valves (Jewson, 1992;

Beszteri et al., 2005). This size diminution can be

accompanied by changes in valve shape, structure and

density of striae, position of marginal fultoportulae and

shape of rimoportulae (Håkansson and Chepurnov,

1999, Meyer et al., 2001, Prasad and Nienow, 2006).

Cell wall variability can also be influenced by shifts in

the environmental conditions such as changes in

salinity, nutrient availability and degree of silification.

These factors have been shown to affect the valve

diameter, the density and shape of striation and costae,

the density of marginal fultoportulae and shape of

satellite pores (Håkansson and Korhola, 1998; Roubeix

and Lancelot, 2008; Shirokawa et al., 2012).

Understanding the mechanisms behind morphological

diversities is thus crucial to identify morphoboundaries

between different taxa and to establish new species.

In the Agios Floros core, species-specific character

variability between the two types of Cyclotella cells is

probably not linked to life-cycle variation of the same

Fig. 18. Vertical profiles (against depth) of bulk sediment geochemistry, δ13C values of n-C23 alkane, accumulation rate (AR),

abundance of diatoms and dissolution index. The red line marks the depth with high abundances of Cyclotella paradistinguenda.

25

species as larger and smaller valves occur in each

population. In addition, there is no evidence for

heterovalvate frustules, although the number of intact

cells encountered in the core was low. The occurrence

of heterovalvy is attributed to the effect of changing

environment or life-cycle variation resulting in

morphological differences between the two valves of a

single frustule (Theriot, 1987; Cox, 2014). In this case,

valves of the same frustule formed at different time and

possibly under different conditions could show distinct

ornamentation pattern, for example, by changing focus

level under LM. The situation related to heterovalvy

also involves morphological variation within a taxon

that is not necessarily continuous, and can alternate

with a change in environmental conditions or cell cycle

(Kociolek and Stoermer, 2010). In the Agios Floros

core, the two type of cells have distinct and constant

character differences and can easily be distinguished

even if found side by side. Their specific distribution

throughout the sequence also indicates that their

ecological separation is important to produce a more

accurate palaeoenvironmental reconstruction.

Therefore, the consilience between the morphological

and palaeo-ecological data suggests that the two

populations should be treated as distinct, and seems to

provide sufficient evidence to recognize a new species.

Cyclotella paradistinguenda is currently classified

as tychoplanktonic/benthic taxon indicating lower water

depth, and highly alkaline and/or even oligotrophic

conditions compared to Cyclotella distinguenda. This

interpretation is based on the correlation between the

distinct distribution of these species and changes in the

litho-stratigraphy, as well as the accompanying diatom

flora. As discussed, Cyclotella paradistinguenda mainly

occurs underneath peat, along with Ellerbeckia

arenaria. In this depth, the diatom abundance is low

with high amount of dissolved vales than in the depths

where Cyclotella distinguenda is the dominant species.

The tychoplanktonic/benthic affinity of Cyclotella

paradistinguenda is further supported by the bulk and

n-alkane carbon isotope data (Fig. 18). The δ13C values

of planktonic species are generally lower (−32 ± 3 ‰)

than those of benthic taxa (−26 ± 3 ‰) (France, 1995;

Doi et al., 2010). This difference is attributed to the

boundary layer (a film of water that sticks to the

surface) effect. Benthic species grow in still water and

have thicker boundary layers resulting in a great

diffusion resistance and in entrapment of otherwise

discriminated 13C (Wang et al., 2013). On the other

hand, planktonic algae are exposed to a greater water

turbulence which reduces the boundary layer thickness

causing more severe 13C depletion (France, 1995).

The Agios Floros δ13C values (bulk and the n-

alkane molecules) are more negative at ca 5700 and at

ca 5300 cal BP where Cyclotella distinguenda is the

dominant species compared to the lake stage at ca 4600

cal BP dominated by Cyclotella paradistinguenda (Fig.

18). This difference is likely related to the specific

carbon isotope signature of different species assuming

much of the sedimentary OM is derived from algae.

The latter is evident from the two older lake stages

characterized by diatomaceous sediments deprived of

plant remains. For the lake stage, at ca 4600 cal BP, the

low C/N ratio (ca 12) points out that the proportion of

allochthonous input is small with possibly higher

contribution from algae, which would give a more

positive imprint in the δ13C values. This suggests that

Cyclotella paradistinguenda lacks the isotopic signature

specific for planktonic species, which supports its

tychoplanktonic/benthic rather than planktonic affinity.

Cyclotella paradistinguenda is only known from

the Agios Floros site without any extant populations.

This indicates that it is likely an endemic species,

representing the Holocene morphological evolution of

the Cyclotella genus in the Peloponnese. Cyclotella

paradistinguenda was likely favored by its capacity to

grow in the environmental settings, which prevailed in

the Agios Floros fen during the lake event at 4600 cal

BP (alkaline/shallow water/low nutrient availability).

8.2.3. Origins of n-alkanes

Sediment samples contain n-alkanes that have been

deposited over years from multiple source plants and

vegetation. Therefore, no single n-alkane homologue

(as extracted from a sediment sample) is expected to

represent an isolated plant group (Norström et al.,

2018). For instance, long-chain n-alkanes can some-

times originate from aquatic sources or a mixture of

aquatic and terrestrial sources (Aichner, 2009). This

relative proportion of contributing plant functional

types can bias the interpretation of n-alkane δD signal.

In addition, δD records can be influenced by various

environmental factors including salinity and vegetation

changes. Therefore, distinction between n-alkanes of

various genetic origins is crucial for a more accurate

interpretation of the δD profiles of individual n-alkanes.

One way to trace the origin of fossil n-alkane is to

perform n-alkanes analysis on the present vegetation. In

particular, Norström et al., 2017 analyzed the n-alkane

concentrations and chain-length distributions of the

most common species of the modern macchia and

phrygana vegetation in SW Peloponnese (Agios Floros

area). The results indicate that the n-alkane production

of drought adapted phrygana herbs and shrubs are six

times higher than the common local reed. In addition,

the reed vegetation is mainly dominated by the n-C27–

C29 alkanes, while phrygana vegetation and Olea

europaea primarily produce n-C31–C35 (Norström et al.,

2017). This vegetation also dominates the area around

the Gialova Lagoon and the Lerna site suggesting

significant contribution of these plants to the fossil

sediment n-alkane pool. However, vegetation in these

areas has changed during the Holocene and this might

have also caused changes in the n-alkane sources. The

interpretation about the origin of n-alkanes can further

be strengthened by combining the analysis on the

present vegetation with various methods including the

down-core n-alkane abundances, their δ13C values and

analysis of plant remains in the sediment cores. In the

26

Gialova study, the combined results from the n-alkanes

isotope analysis and the plant remains analysis indicate

different sources of the individual n-alkanes; n-C17 is

derived from bacteria/algae, n-C23-C25 from aquatic

plants, n-C27-C29 aquatic and terrestrial vegetation

(local fen) and n-C31 mainly comes from terrestrial

vegetation (Phrygana and Olea europaea) (Katrantsiotis

et al., 2018). In the Lerna core, no carbon isotope

analysis was performed and macrofossil remains were

examined at a lower resolution. However, changes in

the carbon chain length distribution clearly show two

distinct sources: n-C23-C25 likely from aquatic plants

(submerged and/or floating plants) and n-C27-C31 from

terrestrial vegetation (Katrantsiotis et al., 2019).

8.2.4. Factors behind δD variability

The development of compound specific δD analysis has

a great potential for hydroclimatic reconstructions.

However, a number of environmental factors influence

the δD values of individual n-alkanes, which can in turn

bias the paleoclimate reconstruction. This holds

especially true for the Peloponnese peninsula, where the

landscape development has been influenced by various

environmental processes including climate changes,

tectonic movements, sea level changes as well as

human impacts. The Peloponnesian sites studied in this

thesis are especially characterized by a long history of

human activities which had a major influence on the

vegetation (Jahns, 1993; Zangger et al., 1997;

Papazisimou et al., 2005). Humans have also influenced

the hydrology of these ecosystems through diverting

rivers or draining lakes during different periods of the

Holocene (Zangger, 1991; Zangger et al., 1997). In

addition, the Gialova and Lerna sites are located close

to the shore and thus sea level changes might further

impact the n-alkane δD records (e.g. lower δD values

during periods of high salinity). Therefore, variation in

sedimentary δD records can be influenced by both

climate and non-climate factors and this must be

understood to improve climate reconstructions. One

way to optimize the interpretative accuracy is to apply a

multiproxy approach derived from independent proxies

(terrestrial and aquatic). Multiproxy studies have the

advantage of providing both complimentary and

comparative information from an area with a complex

landscape development. This can assist in identifying

synchronous changes between different proxies that

could be attributed to a common climate mechanism.

In the present study, the n-alkane δD records

generally covary with each other indicating that they all

reflect changes in δD composition of source water

modulated by a common climate factor. This is further

evident from the n-C17 alkane in the Gialova record and

the n-C23 alkane in the Agios Floros which have a stable

source organism (relatively stable δ13C profile) and,

therefore, the δD variability of these n-alkanes can be

considered as a result of shifts in δD of water. Τhe

Gialova δD profiles also covary with the XRF data

indicating that both proxies respond to a common

hydroclimate signal i.e. the two proxies support each

other. In the Lerna record, there is a good variability of

all n-alkane δD profiles with the Paq and ACL indexes.

These indexes reflect changes in the abundance of

aquatic macrophytes and drought sensitive vegetation,

respectively, which can be attributed to climate factors.

Previous studies have indicated that the Gialova

Lagoon and the Lake Lerna were isolated from the sea

during the studied time-intervals (Zangger, 1991;

Emmanouilidis et al., 2018). Therefore, the δD signal in

water has largely been determined by the balance

between direct precipitation amount and evaporation

rate. The water supply in the studied sites mainly relies

on meteoric water deriving either directly from

precipitation or via rivers and spring flows.

Groundwater δD values from aquifer springs in the

Peloponnese show strong correlation with δDprec

confirmed by low (high) spring flows during dry (wet)

seasons (Dotsika et al., 2018; Norström et al., 2018).

In the eastern Mediterranean region, the water

isotope composition in precipitation (δ18Oprec, δDprec) is

mainly influenced by the temperature with cooler

conditions leading to lower δDprecip (Fig. 19a) (Argiriou

and Lykoudis, 2006; IAEA, 2014; Bolin Centre

Database, Mouzaki, 2017). The amount effect also

plays an important role; high rainfall amounts lead to

more negative isotope values (Fig. 19b) (IAEA, 2014;

Bolin Centre Database, Mouzaki, 2017). On an annual

basis, this relationship is valid for rainfall amount ≤100

mm while on a seasonal basis the amount effect is

stronger during summer rains (Argiriou and Lykoudis,

2006). Other factors affecting δDprecip are changes in air

mass trajectories, associated with the relative

dominance of westerly-northwesterly derived D-

depleted air masses and southwesterly-derived D-

enriched air masses (Argiriou and Lykoudis, 2006;

Dotsika et al., 2010). The isotopic signal of these air

masses may further be modified by the water vapor

produced in the Mediterranean (Dotsika et al., 2010).

The δ18O composition in laminated speleothems

from the central-eastern Mediterranean region is mainly

governed by the amount effect (e.g. Bar-Matthews and

Ayalon, 2004; Zanchetta et al., 2014; Psomiadis et al.,

2018). The Peloponnesian δD records show close

resemblance to speleothem δ18O profiles in this region

(Katrantsiotis et al., 2018, 2019) indicating that the

amount effect has played an important role in the δD

variability. The effects of air temperatures are likely

superimposed on the amount effect process and can be

regarded as a response to the large temperature

variation between summer and winter. Higher summer

temperatures would enhance the δD signal though the

intense evaporation of source water and leaf water.

Nevertheless, on both monthly and annual base, there is

an anticorrelation between the mean air temperature and

total precipitation amount in the Peloponnese (Fig. 19c

and 19d; r=-0.57 and r=-0.69 for the period 2002-2015)

(IAEA Patras, 2014). This indicates that over longer

time scales, periods of lower precipitation were likely

accompanied by higher temperatures and vice versa.

27

Fig. 19. Data from IAEA Patras, NW Peloponnese, for the

period 2001-2015. The correlation between (A) mean

monthly temperature and δD of precipitation (B) monthly

amount of precipitation and δD of precipitation, (C) mean

monthly temperature and monthly amount of precipitation,

and (D) mean annual temperature and annual precipitation.

The latter is based on data for the period 2002-2015.

Taking these factors into account, the variability of

δD n-alkanes from the three studied sites is regarded a

combined response to: (i) δDprec, linked to rainfall

amounts, (ii) evaporation of source water and leaf

waters, coupled to air temperature and (iii) δDlake (lagoon),

determined by evaporation and precipitation/freshwater

input. Therefore, higher δD values in the records

indicate drier (and warmer) conditions, whereas lower

δD values represent wetter (and colder) conditions.

In summary, the above data suggest that a common

climate signal override the vegetation impact changes at

least over longer time-scales while any effect of

increased fractionation under high salinity appears to

have a minimum impact on the δD records (cf. Aichner

et al., 2017). However, abrupt vegetation changes and

tectonic activities might have affected the δD signals

over shorter periods. Hence, the climate reconstruction

presented in this thesis is based on the long-term trends

avoiding interpreting single peaks that might represent

changes in non-climate (e.g. tectonics) processes.

Apart from the application of multiproxy analysis,

another way to optimize the interpretative accuracy is

the comparison of proxy records from SW and NE

Peloponnese and with other regional paleoclimatic

studies. This may give further evidence of synchronous

induced climate changes. Features that appear only in

individual records most likely represent non-climate

variability. On the other hand, changes that occur across

regional records likely represent variations in climate.

8.3. The role of tectonics in abrupt hydro-logical changes in the Agios Floros fen The diatom and isotope data in the Agios Floros core

reveal climate induced long-term trends which resemble

other paleoclimatic signals from the Peloponnese and

beyond. In addition, both proxy data infer abrupt and

short-term hydrological changes mainly at ca 5700 and

ca 5300 cal BP. These two events are likely related to

local environmental factors as they do not appear in

other records from the central-eastern Mediterranean.

The Agios Floros basin is bounded to the east by an

active fault system, i.e. the Agios Floros-Pidima fault

segment, which is a part of the Eastern Messinia Fault

Zone (Fig. 20) (Kassaras et al., 2018). A significant

number of historical and instrumental earthquakes have

been assigned to this specific fault segment. Most

recently, in the period 2011 June–October, a tectonic

swarm of 1222 earthquakes occurred in the hanging

wall of this normal fault zone migrating from NNW

(upper Messinia Plain) towards SSE (Agios Floros)

(Fig. 21) (Kyriakopoulos et al., 2013). In addition, the

Agios Floros-Pidima fault segment is connected to a

karst spring system on the foot of the Taygetos

Mountains. The hydrology of these springs is largely

depending on the rainfall amount but also other tectonic

processes. Increase in the flow rate of springs from

other areas with similar settings have been attributed to

anomalous behaviors of aquifers, due to seismic

stresses before or after earthquakes (Kissin and

Grinevsky, 1990; Muir-Wood and King, 1993; Esposito

et al., 2001). Taking into account the high seismicity

and location of the studied site next to the springs, the

abrupt and short–term water level changes observed in

the Agios Floros record can largely be attributed to

local tectonic processes and the associated earthquakes.

a

b

c

d

28

The Agios Floros basin has a maximum depth of 2

m with an outlet to the south (Norström et al., 2018).

Therefore, the occurrence of high-water events in this

shallow basin at ca 5700 and ca 5300 cal BP would

require deepening (subsidence) of the ground surface

possibly associated with two earthquakes. The

combination of increase in the flow rate of springs

before the earthquakes with the basin subsidence would

trigger water level rise that would be high enough

(possibly ≤10 m) to promote the dominance of

planktonic species i.e. Cyclotella distinguenda, and the

formation of laminated sediments. In addition, these

events are accompanied by high accumulation rates that

can largely be associated with the landscape instability

after earthquakes leading to the shallowing of the lakes.

There is additional evidence for abrupt hydrological

changes in the Messenian plain between 6000-5000 cal

BP. Papazisimou et al., 2005 reported similar lake level

changes in the central Messenia plain based on a pollen

study from the Agios Floros fen. Kraft et al., (1975)

found evidence for a sharp rise of 9 m in the relative sea

level that flooded the lower Messenian plain between

5700 and 5300 cal BP. Engel et al., (2009) showed that

a maximum landward shore displacement occurred at ca

5000 cal BP. Further to the south, ca 50 km from the

site of Agios Floros, archaeological evidence indicate

that the Alepotrypa cave entrance collapsed due to an

earthquake at ca 5200-5000 cal BP (Boyd, 2015). In

the western Greece, multiple regional tectonic events

were detected at ca 6000-4500 cal BP, based on relative

sea level (RSL) curves for seven coastal areas in NW

Greece and the Peloponnese (Vött, 2007). These

regional tectonic events were generally characterized by

changes in the uplift/ subsidence rates and/or by the

redirection of local tectonic movements. In addition, a

sequence of coseismic uplift movements were

reconstructed at the Perachora Peninsula at the eastern

shore of the Gulf of Corinth, NE Peloponnese at ca

6000-4500 cal BP (Pirazzoli et al., 2004). Therefore, it

can be concluded that the tectonic events identified in

the Agios Floros fen seem to coincide with a period of

intense tectonic activity on a more regional scale (a

period of high frequency–high magnitude earthquakes).

In addition to tectonic activities, climate changes

associated with enhanced precipitation might have

contributed to the Agios Floros lake stages. The period

between 6000-5000 cal BP is generally characterized by

wetter conditions in the wider region of the Eastern

Mediterranean (Finné et al., 2011). Therefore, basin

subsidence would be accompanied by high rainfall

events, which would also enhance the spring discharge.

There is a lack of archaeological studies in the

Agios Floros area that could allow us to speculate about

human influence in the landscape changes between

6000 and 5000 cal BP. Nevertheless, the formation of

lakes at ca 5700 and 5300 cal BP are more likely caused

by a natural mechanism, which is evident from the

deepening of the basin as described above and the

undisturbed laminated sequence. Evidence for

vegetation changes associated with human activities,

however, have been found in the lower Messenian plain

and the slopes of Taygetos after 6000 cal BP (Engel et

al., 2009). This might add the possibility that the

infilling of the lakes after these events would have been

caused by high erosion related to human activities on

the nearby slopes of the Taygetos Mountain range.

The lake event at ca 4600 cal BP is different from

the events at 5700 and 5300 cal BP. The former; 1) is

Fig. 20. Topographical map of the Messenian plain and the

surrounding area showing the Eastern Messinia Fault Zone

(Black lines). The Agios Floros area with the springs and the

Agios Floros-Pidima fault segment are depicted in the box.

Fig. 21. Map of the Agios Floros and the surrounding area

(inset box from Fig. 20) showing the magnitudes and the

epicenters of earthquakes occurred in June–October 2011.

The map also highlights the seismicity migration towards

south (reproduced from Kyriakopoulos et al., 2013).

29

dominated by deposits consisting of gyttja clay rather

than diatomaceous laminated clay, 2) is characterized

by a diatom flora dominated by the tychoplanktonic

/benthic species Cyclotella paradistinguenda rather

than the planktonic species Cyclotella distinguenda

(Katrantsiotis et al., 2016), 3) contains a higher amount

of aquatic biomarkers, and 4) shows less abrupt isotopic

proxy response and is more extended in time (Norström

et al., 2018). These factors suggest the dominance of

more shallow water, during the lake event at 4600 cal

BP compared to the previous events. In addition, shifts

in the n-alkane δD values are observed in the Lake

Lerna at ca 4600-4500 cal BP, and thus these changes

can be attributed to a regional climate mechanism.

9. Regional climate reconstruction

The climate reconstruction presented in this thesis is

based on the correlation of the Peloponnesian n-alkane

δD records revealing the dominance of sometimes

similar and sometimes opposing climate signals

between NE and SW Peloponnese. This reconstruction

is further supported by other paleoclimatic studies in

the peninsula. The sedimentary Asea valley record in

the central Peloponnese shows a similar pattern to Lake

Lerna δD23, mainly before 2000 cal BP (Unkel et al.,

2014). The Kapsia cave δ18O record in the central-

eastern Peloponnese covering the period between 2950

and 1170 cal BP exhibits similar long-term trends as the

Lake Lerna δD23 signal (Finné et al., 2014). In SW

Peloponnese, the Alepotrypa Cave δ18O record bears a

close resemblance to Agios Floros δD23, and especially

to the Gialova Lagoon record (Boyd, 2015;

Katrantsiotis et al., 2019). The Mavri Trypa Cave δ18O

signal from this area, however, shows a hiatus between

2950 and 2200 cal BP which has been attributed to both

drier conditions and to the rerouting of water through

the bedrock or human intervention in or near the cave

(Finné et al., 2017). In addition, this record shows

wetter conditions between 1800 - 1650 cal BP followed

by an aridification trend when the Gialova and Agios

Floros signals also point to a period of enhanced aridity.

The Peloponnesian δD records are divided into

different climate zones representing periods of humidity

(and temperature) changes. These signals are further

integrated with other paleoclimate studies from the

Mediterranean region to provide an updated assessment

of the spatial climate variability during the last 5000

years. The comparison reveals large intra-regional

variability. The Agios Floros-Gialova records appear

sometimes synchronous with the western-central

Mediterranean studies (e.g. 3900-3000, 3000-2600,

700-300 cal BP) while the Lake Lerna signal sometimes

matches other records from the eastern Mediterranean

(e.g. 4500-4200, 2600-1800 cal BP). However, similar

signals between SW and NE Peloponnese can also be

observed during periods of large-scale events (4.2 and

2.8 ka events, MCA, LIA). The periods described

below are based on the Peloponnesian signals, also

plotted with selected Mediterranean records on a map to

visualize the spatial distribution (Table 1, Fig. 22).

5000-4500 cal BP. Wetter conditions dominate the

Peloponnese until 4600 cal BP when the NE part of the

peninsula becomes drier between 4600-4500 cal BP.

There is evidence for wetter and warmer conditions in

the Aegean Sea during this period (Triantaphyllou et

al., 2009; Psomiadis et al., 2018). In the wider

Mediterranean region, high humidity is reported from

southern Italy (Magny et al., 2011) and also the Levant

region (Bar-Matthews and Ayalon, 2004; Cheng et al.,

2015). Conversely, increased aridity is inferred from the

Anatolian region (Göktürk et al., 2011; Kuzucuoğlu et

al., 2011), northern Italy (Magny et al., 2007) and the

western Mediterranean, mainly from the Iberian

Peninsula (Frigola et al., 2007; Jalut et al. 2009). 4500-4100 and 4100-3900 cal BP. High humidity is

evident in the Peloponnese until ca 4200 cal BP

followed by an aridification trend at ca 4100-3900 cal

BP. The wet conditions in the SE Aegean Sea terminate

at ca 4300 cal BP (Triantaphyllou et al., 2009). In the

northern Aegean Sea, there is evidence for drier

conditions after ca 4100 cal BP (Psomiadis et al., 2018)

while similar conditions are reported from the western

Balkans (Zanchetta et al., 2012). A shift towards high

humidity is reported from the Anatolian region

(Göktürk et al., 2011; Kuzucuoğlu et al., 2011) and the

northern Italy with more unstable conditions at ca 4100-

3900 cal BP (Magny et al., 2007). An aridification trend

superimposed by more unstable conditions is reported

from the Levant region (Bar-Matthews and Ayalon,

2004; Cheng et al., 2015). Drier conditions are evident

in southern Italy (Magny et al., 2011) and also the

Iberian Peninsula throughout these time-intervals

(Martín-Puertas et al., 2008; Jalut et al. 2009). The

picture of the time at ca 4200 cal BP in the Eastern

Mediterranean as a pronounced dry period is supported

in records from across the region and also coincides

with the decline of the Akkadian Empire in northern

Mesopotamia and the Old Kingdom of Egypt (Weiss et

al., 1993; Cullen et al., 2000 Stanley et al., 2003). 3900-3000 cal BP. This period is characterized by an

opposite climate signal in the Peloponnese; wetter

conditions are evident in NE and drier conditions in SW

with a reversal at ca 3300-3200 cal BP. More unstable

conditions dominate the northern Aegean region with

higher humidity at ca 3700-3500 and after ca 3400 cal

BP (Psomiadis et al., 2018). Alternate wet/dry episodes

are reported from the central Anatolian (Kuzucuoğlu et

al., 2011) and the southern Levant (Bar-Matthews and

Ayalon, 2004). A wetter climate regime is inferred from

the northern Levant (Cheng et al., 2015) and NNW

Turkey (Göktürk et al., 2011). An aridification trend is

reported from the western Balkans (Zanchetta et al.,

2012), in line with other records in southern (Magny et

al., 2007; Piccarreta et al., 2011) and northern Italy,

which indicate lower lake levels interrupted by a wet

spell at ca 3300 cal BP (Magny et al., 2007, 2011). In

the Iberian Peninsula, most of the records report

30

enhanced aridity during this period (Martín-Puertas et

al., 2008 and references therein; Jalut et al., 2009). 3000-2600 cal BP. The Peloponnesian δD records

generally show the dominance of wetter conditions in

the peninsula with more abrupt hydrological shifts in

SW Peloponnese. High humidity is inferred from the

northern Aegean region and the central Greece until ca

2600-2400 cal BP (Pavlopoulos et al., 2006; Psomiadis

et al., 2018). More arid conditions are mainly reported

from NNW Turkey (Göktürk et al., 2011) and the

northern Levant (Cheng et al., 2015) compared to the

central Anatolian (Kuzucuoğlu et al., 2011) and

southern Levant region (Bar-Matthews and Ayalon,

2004). In general, there is a trend towards enhanced

aridity in the Eastern Mediterranean after ca 3200 cal

BP (Roberts et al., 2001; Finné et al., 2011; Kaniewski

et al., 2013). Conversely, wetter or more unstable

conditions compared to the previous period are reported

from the western Balkans (Zanchetta et al., 2012), and

southern and northern Italy (Magny et al., 2007, 2011).

In the western Mediterranean (southern Iberia) there is

a shift from a prolonged period of drought to wetter

conditions from ca 3000-2800 cal BP (Martín-Puertas et

al., 2008 and references therein). This coincides with an

increased wetness in many European bogs (Borgmark

and Wastegård, 2008; Engels and van Geel, 2012). 2600-1800 cal BP. Roman Warm Period (RWP). This

period is characterized in the Peloponnese by a SW-NE

opposite climate regime with intense aridity prevailing

in the NE part. There is evidence for drier conditions in

the north Aegean Sea during this period (Psomiadis et

al., 2018). An aridification trend is also reported from

NW Turkey (Göktürk et al., 2011) and the Levant

region (Bar-Matthews and Ayalon, 2004; Cheng et al.,

2015), whereas records from central Anatolia show

both wet (Kuzucuoğlu et al., 2011) and dry conditions

(Dean et al., 2015). In the western Balkans and Italy,

studies provide no coherent picture. However, it seems

that relatively drier conditions prevail in the northern

Italy (Magny et al., 2007) and Sicily (Magny et al.,

2011) while in the Gulf of Taranto region (Piccarreta et

al., 2011; Grauel et al., 2013) and the western Balkans

(Zanchetta et al., 2012) a wet period is followed by an

aridification trend after ca 2000 cal BP. In the Iberia

peninsula, paleoclimatic records indicate the gradual

dominance of wetter and warmer conditions (Martín-

Puertas et al., 2008; Nieto-Moreno et al., 2011). 1800-1300 cal BP. Dark Ages Cold Period (DACP).

The Peloponnesian records infer a reversal of the

previous W-E climate signal, with more pronounced

aridity now being evident in SW Peloponnese. Similar

to NE Peloponnese, high humidity is reported from the

northern Aegean after 2000 cal BP (Psomiadis et al.,

2018) with colder conditions between ca 1500 and ca

1150 cal BP (Gogou et al., 2016). A shift from drier to

wetter conditions at ca 1500 cal BP is inferred from

Anatolia (Göktürk et al., 2011; Kuzucuoğlu et al., 2011;

Dean et al., 2015) and the southern Levant (Bar-

Matthews and Ayalon, 2004) in contrast to the northern

Levant (Cheng et al., 2105). At the same time, a trend

towards high humidity is also inferred from southern

Italy (Piccarreta et al., 2011; Grauel et al., 2013; Sadori

et al., 2016). On the other hand, enhanced aridity is

reported from the western Balkans (Zanchetta et al.,

2012) and northern Italy (Magny et al., 2007). Further

west, a trend towards drier conditions is revealed in the

Iberian Peninsula mainly after ca 1600 cal BP (Martín-

Puertas et al., 2008; Nieto-Moreno et al., 2011). 1300-700 cal BP. Medieval Climate Anomaly (MCA).

There is a trend towards an abrupt wetness at ca 1300-

1200 cal BP followed by more arid conditions in SW

Peloponnese. On the other hand an aridification trend is

evident in NE Peloponnese throughout this period.

More unstable conditions are reported from the North

Aegean Sea with an arid and warmer period at ca 1000-

800 cal BP (Gogou et al., 2016). Similar to SW

Peloponnese, a shift from wetter to drier conditions is

inferred from the central Anatolian (Kuzucuoğlu et al.,

2011; Dean et al., 2015) whereas an aridity signal

through this period is evident from NNW Turkey and

the southern Levant region (Bar-Matthews and Ayalon,

2004). More arid conditions are also inferred from the

western Balkans (Zanchetta et al., 2012). In general,

records from the central Mediterranean are in

agreement with the Gialova record showing the

dominance of enhanced aridity in the second half of the

MCA (Magny et al., 2007; Piccarreta et al., 2011;

Grauel et al., 2013; Sadori et al., 2016). Conversely,

drier condition are reported from the western

Mediterranean, mainly from the southern part of the

Iberian Peninsula throughout the MCA period (Martín-

Puertas et al., 2008; Nieto-Moreno et al., 2011). 700-200 cal BP. Little Ice Age (LIA). The records in

the Peloponnese generally infer the dominance of

wetter conditions, which are more intense in the SW

parts. Increased wetness is reported from the North

Aegean Sea after ca 600 cal BP, accompanied by

fluctuations in SSTs (Gogou et al., 2016). The records

from the Eastern Mediterranean do not provide a

coherent picture. More unstable conditions are reported

from NNW Turkey (Göktürk et al., 2011) while a shift

from wet to dry conditions is reported the southern

Levant (Bar-Matthews and Ayalon, 2004). Both wet

and dry conditions are indicated from the central

Anatolian (Kuzucuoğlu et al., 2011; Dean et al., 2015).

Enhanced aridity is inferred from the western Balkans

(Zanchetta et al., 2012). In the wider region of the

central Mediterranean, there is evidence for the

development of wetter and colder conditions during the

LIA (Piccarreta et al., 2011; Grauel et al., 2013; Sadori

et al., 2016). In the western-central Europe this period

starts with the alpine glacier advance and increase in

lake levels at ca 700 cal BP (Frisia et al., 2005;

Holzhauser et al., 2005). This is in agreement with

other western Mediterranean records which indicate a

gradual shift to a wetter period (Martín-Puertas et al.,

2008; Nieto-Moreno et al., 2011; Roberts et al., 2012).

31

Table 1. A compilation of paleoclimate records from the Peloponnese and the Mediterranean region with full references. Codes

correspond to Fig. 22. Information regarding the location and the type of sites, the proxies and the periods covered in each study.

Code Reference Location Site type Proxy Time

interval (cal

BP)

P1 Norström

et al., 2018

SW Peloponnese,

Greece

Agios Floros Fen-

Paleolake

Sediment core, δD23 Last ∼5000

P1 Katrantsiotis

et al., 2018

SW Peloponnese,

Greece

Gialova Lagoon Sediment core, δD31 Last ∼3600

P2 Katrantsiotis

et al., 2019

NE Peloponnese,

Greece

Ancient Lake

Lerna-Wetland

Sediment core, δD23 Last ∼5000

A1 Triantaphyllou

et al., 2009

SE Aegean Sea

Greece

Marine Sediment core,

Biological and

geochemical records

Last ∼13000

A2 Psomiadis

et al., 2018

Thassos Island,

Greece

Skala Marion

Cave

Speleothem δ18Ο Last ∼5000

A3 Gogou

et al., 2016

North Aegean Sea Athos basin

Marine

Sediment core,

Biological and

geochemical records

Last ∼1500

T1 Göktürk

et al., 2011

NNW Turkey

/South Black Sea

Sofular Cave Speleothem δ13C Last ∼14000

T2 Kuzucuoğlu

et al., 2011

Central Anatolian

plateaux

Tecer Lake Sediment core,

mineral content and

grain-size

Last ∼6000

T3 Dean

et al., 2015

Central Anatolian

plateaux

Nar Gölü-

Brackish maar

lake

Sediment core, δ18Ο

carbonate Last ∼4500

M1 Cheng

et al., 2015

Northern Levant Jeita Cave Speleothem δ18Ο,

δ13C, Sr/Ca Last ∼20000

M2 Bar-Matthews and

Ayalon, 2004

Southern Levant Soreq cave Speleothem δ18Ο, δ13C Last ∼14000

B1 Zanchetta

et al., 2012

Western Balkans

Albania/

Montenegro

Lake Shkodra Sediment core, δ18Ο

carbonate Last ∼4500

C1 Magny

et al., 2007

Northern Italy

(Tuscany, Italy)

Lake Accesa Sedimentological

techniques Last ∼11500

C2 Magny

et al., 2011

Lago Preola (Sicily,

southernItaly)

Lake Preola Sedimentological

techniques Last ∼11000

C3 Piccarreta

et al., 2011

Basilicata region,

southern Italy,

floodplain Sedimentological/

morphological

techniques

Last ∼8000

C4 Grauel

et al., 2013

Southern Italy Gulf

of Taranto

Marine Sediment cores,

δ18O and δ13C of Globigerinoides ruber

Last ∼2500

C5 Sadori

et al., 2016

Sicily Lago di Pergusa

(Lake)

Sediment cores,

pollen and δ18O and

δ13C from carbonates

Last ∼2000

W1 Jalut et al., 2009

and Carrión

et al., 2001

Southern-central

Iberian Peninsula

Synthesis of

terrestrial records

Sediment cores, pollen Last ∼10000

W2 Martín-Puertas

et al., 2008

Southern Iberian

Peninsula

Zoñar Lake Sediment core,

biological records Last ∼4000

W3 Nieto-Moreno

et al., 2011

Western

Mediterranean Sea

Marine Sediment core,

geochemical records Last ∼4000

32

Fig. 22. Maps illustrating the pattern of climate variability in

the Mediterranean region over the last 5000 years based on

the comparison of selected climatic proxies with the

Peloponnesian δD records. Colored dots indicate climate

interpretation in the proxy records. Site numbers and letters

correspond to the numbers and letters (code) in Table 1.

Spatial variability between the maps reveals a regional drying

trend from 4100 to 3900 cal BP and from 1300 to 700 cal BP

(MCA). Changes to wetter conditions seem to have occurred

at 3000-2600 cal BP and between 700 and 200 cal BP (LIA).

33

10. Drivers of Holocene climate variability

The Holocene (ca last 11000 years) is characterized by

low-frequency millennial-scale climatic oscillations; an

early-middle Holocene warm period, followed by a

cooling trend after ca 5000 cal BP that ended with the

present global warming (Renssen et al., 2012; Marcott

et al., 2013). This variability has been attributed to

orbitally driven changes in the incoming solar radiation

at the top of the atmosphere (insolation) during boreal

summer (Lorenz et al., 2006; Wanner et al., 2014).

An increasing number of proxies around the world

indicate that the Holocene low-frequency climatic

oscillations are superimposed by a series of century-to-

millennial scale changes (Mayewski et al., 2004;

Wanner et al., 2011). In particular, repeated climate

shifts at periodicities of 2500 and 1000 years have been

associated with changes in the solar influx (Debret et

al., 2007). In addition to this variability, there is

evidence for climate cycles of 1500 years attributed to

oceanic circulation changes (Bond and Lotti, 1995;

Mayewski et al., 1997; Debret et al., 2007). These cold

events (Bond cycles) were discovered as horizons of ice

rafted debris (IRD) in sediment cores from the North

Atlantic (Heinrich, 1988; Bond et al., 1997, 2001).

Subsequent studies have shown the impact of the Bond

cycles at lower latitudes (e.g. Sierro et al., 2005; Smith

et al., 2016). However, evidence of these events is not

always found in paleoclimate records as each region or

proxy have likely responded differently (Wanner et al.,

2011; Moossen et al., 2015). The mechanisms causing

these high frequency climate events are not well-

understood. It has been suggested that during the early

Holocene these changes were caused by the slowdown

of the Atlantic overturning circulation due to meltwater

fluxes in the North Atlantic (Wanner et al., 2014). Late

Holocene events have also been attributed to volcanic

and solar forcing and the complex interactions between

ocean and atmosphere (Breitenmoser et al., 2012;

PAGES 2k Consortium, 2013; Wanner et al., 2014).

In the Mediterranean region, climatic conditions

have varied both spatially and temporally during the

Holocene due to the complex landscape and the impacts

of different atmospheric modes (Dormoy et al., 2009;

Magny et al., 2012; Roberts et al., 2012). In particular,

several processes have been put forward as potential

drivers of the Mediterranean climatic variability such as

the North Atlantic Bond cycles (Bond et al., 2001; Dean

et al., 2015) and the large variations in the high-latitude

atmospheric patterns (NAO, NCP) (Cullen et al., 2002;

Kutiel et al., 2002). In addition to these modes, the

African and Asian monsoons have been considered as

one of the key factors of the Holocene Mediterranean

hydroclimate (Jones et al., 2006; Dean et al., 2015).

10.1. High latitude atmosphere patterns

The Peloponnesian studies offer the opportunity to

investigate the impact of large-scale teleconnections in

the Mediterranean. Variations in δD records from NE

and SW Peloponnese show similar and sometimes

opposing climate signals attributed to the effects of

different atmospheric modes (NAO, NCP). The similar

signals at ca 4500-3900, ca 3000-2600 and after ca

1000 cal BP coincide with shifts in the reconstructed

NAO (Olsen et al., 2012; Katrantsiotis et al., 2019).

This indicates that the NAO was exerted the main

control with positive (negative) NAO phases creating

drier (wetter) conditions. In addition, cooling events in

the North Atlantic (peaks in IRD curve) coincide with

trends to arid episodes in the Lerna record before ca

3300 cal BP and thereafter there is a coincidence with

wetter time-intervals (Bond et al., 2001; Katrantsiotis et

al., 2019). In the eastern Mediterranean region, the

Bond events have been associated with enhanced

aridity. This has been attributed to cold-water input into

Mediterranean Sea as a result of the collapse of the

North Atlantic Deep Water circulation leading to a

reduction of evaporation and thereby less precipitation

(Bartov et al., 2003). In the western Mediterranean, a

noticeable positive correlation between winter rain

minima and Bond events was found during the early

Holocene and an opposite pattern during the late

Holocene (Zielhofer et al., 2018). Periods of increase in

storm activity in the French Mediterranean coast were

also correlated with peaks in the IRD record attributed

to the southward displacement of storm track as a result

of complex oceanic-atmospheric interactions (stronger

meridional temperature gradient due to the southward

extension of the sea ice) (Raible et al., 2007; Sabatier et

al., 2012). Overall, these data indicate that there is a

link between the climate variability in the North

Atlantic and the Mediterranean climate. However, it

remains unclear which mechanism causes sometimes

dry and sometimes wet conditions in the Peloponnese in

response to cooling events in the North Atlantic region.

Although NAO is one of the dominant modes of

variability over the central-eastern Mediterranean, other

atmospheric modes have also played an important role.

In particular, the opposite signal observed between NE

and SW Peloponnese during some periods can be

explained by the dominance of the NCP over the

peninsula, which also accounts for the present day

climate variability (Kutiel et al., 2002). At ca 3900-

3300, ca 3200-3000 and ca 1800–1300 cal BP, positive

NCP phases would lead to the intrusion of N-NE cold

air masses over the Aegean Sea creating wetter and

colder conditions in NE Peloponnese. Conversely, at ca

4600-4500, ca 3200, ca 2600–1800, and 1200-1000 cal

BP, more negative NCP phases would result in a

southwesterly anomalous circulation causing wetter

conditions in SW Peloponnese and relatively drier in

NE Peloponnese as this area is located on the leeward

side of the mountain in relation to the westerly winds.

10.1.1. Physical Mechanism

Overall, the similar and sometimes opposing climate

signals between NE and SW Peloponnese can mainly

be explained by shifts in the dominance between the

34

NAO and the NCP over the area of the central-eastern

Mediterranean. The mechanism, which is responsible

for this variation, is not well-known. However, since

both of the NCP and the NAO occur in the Northern

Hemisphere, it is expected that they would interact with

each other. In particular, it has been shown that the East

Atlantic/West Russia (EA/WR) pattern, which is the

more regional expression of NCP, is sensitive to the

NAO phases (Lim, 2015). In general, EA/WR-like

blocking pattern has been found to be better organized

and strengthened over the Atlantic and Western Europe

when the NAO is also characterized by more positive

phases (Lim, 2015). During these periods, the eastward

propagation of the EA/WR pattern is likely facilitated

by the stronger upper level westerly jet (Atlantic Jet) at

40–60°N, whose exit points towards Scandinavia (Fig.

23a). The stronger pressure patterns and atmospheric

blocking over Europe favor cold air advection towards

the Eastern Mediterranean leading to wetter and colder

conditions in areas exposed to northerly winds, such as

the eastern Peloponnese (Fig. 23b and Fig. 25a).

However, these conditions are mainly dependent on the

position and extension of blocking system over Europe.

An eastward extension of high pressure system would

result in drier and warmer conditions even in the areas

exposed to northerly winds. On the other hand, a less

well-organized EA/WR-like blocking pattern has been

simulated when the NAO is characterized by more

negative phases (Lim, 2015). This results in weaker

pressure patterns and associated blocking over Europe

as the low pressure anomalies are situated further west

over Greenland due to the weakened upper-level

westerlies (Wanner et al., 2001). During these periods,

the axis of the Atlantic Jet is shifted southward, and

therefore the south-western Europe receives more

precipitation (Fig. 24a) (Ionita, 2014). In the eastern

Mediterranean region, low pressure systems originating

from the Atlantic region and the western Mediterranean

produce higher precipitation amount mainly in the areas

exposed to westerly winds (Fig. 24b and Fig. 25b).

Fig. 23 (a) Atmospheric circulation pattern over Europe

during positive EA/WR (NCP) and NAO modes (b)

Predictive distributions of daily accumulated precipitation in

Greece for 8 January 2019. EA/WR (NCP) index was in a

positive phase. Map with precipitation data were obtained

from the numerical model simieteo.gr

Fig. 24 (a) Atmospheric circulation pattern over Europe

during negative EA/WR (NCP) and NAO phases (b)

Predictive distributions of daily accumulated precipitation in

Greece for 22 January 2019. EA/WR (NCP) index was in a

negative mode. Map with precipitation data were obtained

from the numerical model simieteo.gr

a b

b a

35

Throughout the late Holocene, shifts in the NAO

and EA/WR modes have affected the precipitation

pattern over the Mediterranean in a similar way. It has

been shown that there was a trend towards drier

conditions in the central Mediterranean and Turkey and

wetter in Israel between 2700 and 1800 cal BP, when

the North Atlantic was relatively warmer, and the jet

stream was located northward (stronger Polar Vortex;

NAO+), (Dermody et al., 2012). The initiation of a

period of cooler North Atlantic SSTs (ca 1800 cal BP)

coincided with an opposite pattern of precipitation.

The results of this thesis indicate the dominance of

more persistent EA/WR-like blocking patterns (positive

NCP) over the western-central Europe at ca 3900–3300,

ca 3200-3000 and ca 1800–1300 cal BP. During these

periods, more frequent cold air advections over the

Aegean Sea associated with this blocking pattern would

cause wetter and colder conditions in NE Peloponnese

(Fig. 23). On the other hand, EA/WR-like blocking

patterns should have been less frequent at ca 4600-

4500, ca 3200, ca 2600–1800, and ca 1200-1000 cal

BP. This would favor the development of cyclone

activity over the western-central Mediterranean creating

wetter conations in SW Peloponnese and relatively drier

and warmer in NE Peloponnese (Fig. 24). The similar

signals during the rest periods are possibly associated

with large scale atmospheric changes as discussed

above (10.1). Aridity signals from both SW and NE

Peloponnese at 4100-3900 (likely 4.2 ka event) and

1000-700 cal BP (MCA), are possibly associated with a

more eastward extension of high pressure system over

the European mainland (positive NAO phases). The

wetter conditions at ca 4500-4200, 3000-2600 (2.8 ka

event), 700-200 cal BP (LIA) are likely related to large-

scale cold air outbreaks from high-latitudes combined

with increased cyclonic activities during more negative

NAO phases (Weninger et al., 2009; Olsen et al., 2012).

10.2. Effects of African and Asian monsoons

The Eastern Mediterranean is indirectly exposed to the

influence of the African and Asian monsoonal systems.

Paleoclimatic records from this region have previously

confirmed the impact of the low-latitude atmospheric

patterns on the Mediterranean hydroclimate changes

during the late Holocene (Jones et al., 2006; Dean et al.,

2015). Therefore, in addition to high-latitude

atmospheric patterns, shifts in the Peloponnesian δD

records are likely associated with changes in the

intensity of monsoons and/or shifts in the relative

dominance of the African monsoons and the Asian

monsoonal systems over the Eastern Mediterranean.

There is evidence for wetter conditions in the

Peloponnese between ca 5000-4600 cal BP when the

NAO was more positive. Similar climate signals are

also observed in other studies from the southern

Mediterranean (e.g. Aegean Sea-Triantaphyllou et al.,

2009; southern Italy-Magny et al., 2011). The Mid-

Holocene represents a period of redistribution of solar

energy due to orbital forcing. This resulted in a

progressive decrease in Northern Hemisphere summer

insolation and southward shift of the ITCZ

accompanied by a pronounced weakening of the

monsoonal systems (Wanner et al., 2008). The

southward migration of low latitude atmospheric

patterns would lead to a decrease in the Hadley

circulation and the accompanied North Atlantic

anticyclone (Tzedakis et al., 2009). This would unblock

possible intrusion of western humid airflow towards the

Mediterranean resulting in wetter climate conditions.

After ca 4500-4000 cal BP, the Hadley cell

circulation that has displaced southwards and weakened

cannot be used indiscriminately to explain the summer

climate variability. Instead, during this period, the

convection has been enhanced over India and has been

Fig. 25 (a) Predictive distributions of accumulated total

precipitation in Greece during a period (26-31/12/2016) with

positive EA/WR (NCP) index. (b) Predictive distributions of

accumulated precipitation in Greece during a period (21-

30/01/2019) with negative EA/WR (NCP) phase. Data were

obtained from Global Forecast System and meteociel.fr.

a

b

36

very limited over North Africa. This implies that the

Asian monsoonal system has played a more important

on the summer conditions of the Eastern Mediterranean

after 4500-4000 cal BP though modulating the strength

of the large-scale subsidence and the intensity of the

Etesians (Ziv et al., 2004; Rizou et al., 2018). The

action centers of these two atmospheric patterns are

located over the wider region of Crete and the Aegean

Sea, respectively (Tyrlis et al., 2013). The interplay

between these two atmospheric patterns, along with the

complex topography in the Peloponnese, leads to a W-E

a see-saw pattern in summer temperatures over the

peninsula. In this respect, the opposite δD trends from

SW and NE Peloponnese might be related to some

extent to the influence of the Asian monsoons. In

particular, there is a consistency between the

Peloponnesian δD signals with monsoonal records from

the Arabian Sea and South-East Asia; intense monsoons

correspond to time-intervals of colder conditions

(lower δD values) in NE Peloponnese and warmer

conditions in SW Peloponnese (Katrantsiotis et al.,

2018, 2019). The site of Lerna is exposed to summer

northerly winds (Etesians) leading to a rapid decrease in

water temperatures and lower evaporation (Giadrossich

et al., 2015; Katrantsiotis et al., 2019). SW Peloponnese

is located on the lee side of the mountain and thus is

most affected by adiabatic warming associated with the

large scale subsidence compared to NE Peloponnese.

It can be concluded that the African monsoonal

system had major impact mainly affecting the summer

precipitation before 4500 cal BP. The Asian monsoonal

system had a major influence on summer temperature

changes in the Peloponnese mainly after ca 4000 cal

BP. These effects of monsoonal systems are likely

superimposed on the precipitation signal associated

with the impacts of high-latitude atmospheric patterns

enhancing the δD variability. In addition, other major

climate events such as the MCA and the LIA might

have larger impact in our records outbalancing the

influences of the Asian monsoons during these periods.

11. Conclusions

This thesis presents multiproxy records of climatic and

environmental changes in the Peloponnese peninsula,

SW Greece over the last 6000 years. The analyses were

performed on radiocarbon-dated sediment cores from

the Agios Floros fen and the Gialova Lagoon in SW

Peloponnese and the Ancient Lake Lerna in NE

Peloponnese. The combined dataset mainly consists of

diatoms, distribution and compound-specific δ13C and

δD composition of n-alkanes and XRF elemental

profiles. The high resolution multiproxy record from

the Agios Floros fen enables identification of short-term

events that can be attributed to local tectonic processes.

In addition, the multiproxy approach from all sites has

contributed to the identification of synchronous changes

between the records that can be attributed to a common

climate mechanism. The location of the sites in two

different climatic zones of the peninsula has contributed

to the development of a dense network of paleoclimatic

records. The integration of data allows us to reconstruct

changes in the E-W climate gradient, to stress local

climate differences and provide a more accurate

assessment of the regional climatic signal over the last

6000 years. Overall, the results of this thesis provide

evidence for long-term climatic changes in the

Peloponnese, associated with the climate variability in

the Eastern Mediterranean. This variability is attributed

to changes in the large-scale atmospheric circulation

patterns from the high-latitude and low-latitude regions. The main conclusions can be summarized as follows: The diatom and n-alkane δD records from the Agios

Floros fen provide evidence for abrupt water level

changes at ca 5700 and ca 5300 cal BP. These

changes are largely attributed to two periods of

earthquakes, which caused basin-subsidence and

increased water flow from the nearby karst springs.

These two events also seem to coincide with an

intense tectonic activity on a more regional scale.

Another period of low to intermediate water level

was identified at ca 4600 cal BP. This period is

dominated by the new fossil diatom species

Cyclotella paradistinguenda described in this thesis.

This species likely represents the Holocene

morphological evolution of the Cyclotella genus in

the Agios Floros site. Cyclotella paradistinguenda

was favored by its capacity to grow in the specific

environmental settings, which prevailed at that time

(alkaline/shallow water/low nutrient availability).

The Agios Floros fen gradually began to develop

after ca 4500 cal BP likely due to a combination of

human activities and also drier conditions. There is

evidence for return to wetter conditions with marked

rainfall seasonality from ca 2800 cal BP.

The n-alkane δD profiles and the XRF data analyzed

in the Gialova core show similar patterns of

variability. This reveals a common climate signal in

SW Peloponnese during the last 3600 years, which

also resembles the Agios Floros record.

The n-alkane δ13C values from the same core

indicate high contribution of aquatic vegetation to

sedimentary OM with the expansion of submerged

plants corresponding to wet and cold periods.

The δD signals of macrophyte and leaf wax-derived

n-alkanes from the Lake Lerna show a nearly

identical pattern to each other providing further

evidence for precipitation and temperature changes

in NE Peloponnese over the last 5000 years.

The synthesis of all proxies indicates sometimes

similar and sometime opposing climate signal

between NE and SW Peloponnese. This can be

attributed to the relative dominance of the low-

latitude and high-latitude atmosphere patterns.

The NAO likely exerted the main control with

negative phases creating conditions of increased

moisture in the Peloponnese at ca 4500-4100, ca

3000-2600 and after ca 700 cal BP. Drier periods at

37

ca 4100-3900 and ca 1000-700 cal BP coincides

with more positive NAO phases. Overall, these dry

and wet periods correspond to large-scale climate

events associated with atmospheric circulation

changes in the North Atlantic region and beyond.

The opposing signal observed between NE and SW

Peloponnese during some periods can be explained

by the dominance of the NCP over the peninsula. At

ca 3900-3300, ca 3200-3000 and ca 1800-1300 cal

BP, positive NCP phases are likely associated with

more persistent blocking systems over the central-

southern Europe that could enhance north-

easterly advection of cold air towards the Eastern

Mediterranean. This would lead to the intrusion of

the N-NE cold air masses over the Aegean Sea

creating wetter and colder conditions in areas

exposed to northerly winds such as NE

Peloponnese. On the other hand, at ca 4600-4500, ca

3200, ca 2600–1800, and 1200-1000 cal BP, more

persistent negative NCP phases are likely related to

weaker pressure patterns and associated blocking

over the southern-central Europe. During this

period, the axis of the Atlantic Jet is shifted

southward, and thus the south-western part of

Europe receives higher precipitation amount. This

southwesterly circulation would cause wetter

conditions in SW Peloponnese and relatively drier

in NE Peloponnese located on the leeward side of

the mountain range in relation to the westerly winds.

The regional climate signal detected in the present

study suggests that the biomarker isotope approach

can provide valuable paleoclimatic information in a

region with a complex landscape, which has evolved

in response to various environmental factors.

12. Future perspectives

This PhD project contributes to a better understanding

of palaeoclimate and paleoenvironmental changes in the

Peloponnese during the last ca 6000 years. However,

additional studies could improve the understanding and

interpretation of available data from the peninsula.

Accurate chronological dating is essential for a

more robust inter-regional correlation between different

palaeoclimate records. Although, the chronologies from

the Peloponnesian sites should be considered reliable,

there is still possibility to improve the age depth models

for some parts of the records (i.e. Agios Floros 700-200

cm; Gialova 150-110 cm; Lerna 250-150 cm). Future

proxy studies on the same cores could perform AMS

dating of pollen concentrate samples due to the absence

of macrofossil plant remains. In this case, it is also

important to ensure that pollen grains in the samples are

derived from terrestrial plants to avoid biases related to

reservoir effects. Although the use of pollen for dating

is relatively rare, previous studies have shown that

pollen can provide reliable chronologies (Brown et al.,

1989; Fletcher et al., 2017). To test the reliability of this

method, dates obtained from pollen can be compared to

AMS dates derived from seeds of terrestrial plants.

Overall, the applicability of radiocarbon dating

method in sediments with low organic carbon content

and a lack of macrofossils is limited. Another way to

improve the chronology is to retrieve new cores from

the same spots that can be dated by employing a

combination of dating techniques. For instance, both

radiocarbon and optically stimulated luminescence

(OSL) dating methods can be applied to test their

suitability for establishing a chronology. The OSL

method should be suitable for the studied sites as the

sediment contain sufficient sand-sized quartz or

feldspar grains in these depths where the organic

content is low. The establishment of new age-depth

models from the same sites would further allow for

cross-correlation of ages between the different records.

Future studies should increase the sample

resolution, especially from the Agios Floros fen and

Gialova records, with emphasis on the period covering

the last 3500 years. This could enable a more accurate

correlation with other regional records in NE

Peloponnese. Other proxies such as pollen could also be

used to facilitate the interpretation, and to investigate

the impact of humans in vegetation changes. The

comparison of pollen with the n-alkane δD data from

the same cores would further allow investigating any

effects of vegetation changes on the isotope data.

A quantitative reconstruction of past climatic

changes based on n-alkanes δD records requires a good

understanding of the H isotope fractionation between

source water and biomass (e.g. Garcin et al., 2012).

Thus, it is important to establish regional calibrations

relating lipid δD values with lake and precipitation δD

values. Future studies in the Peloponnese could

measure the δD values of n-alkanes in surface

sediments, and the δD composition of modern

vegetation and in water sources, including lake water,

groundwater and precipitation. This approach would

enhance our understanding of the links between the δD

values of sedimentary lipid biomarkers and their

respective hydrogen sources. Τhis is an important step

for quantifying past hydroclimatic changes in this area.

Quantitative reconstruction of lake-level changes

based on diatoms has so far not been attempted in the

wider region of Greece due to the lack of modern

diatom analogues. The reconstruction of maximum lake

level changes in the Agios Floros fen was mainly based

on the habitat preference of Cyclotella distinguenda

from the Alpine datasets. Therefore, modern diatom

samples from lakes and wetlands in the Peloponnese

should be analyzed to establish a reliable transfer

function. Modern datasets in conjunction with lake-

morphometric data could allow us to quantify the

Holocene lake-level shifts in Agios Floros accurately.

The causes behind the abrupt water level changes in

the Agios Floros fen need to be investigated in close

detail. A number of factors indicate that these events

are associated with local tectonic process, which needs

to be confirmed. Firstly, successive coring could be

38

performed on a longitudinal section along the fen to

establish the maximum depth and extension of lakes.

Secondly, sediment cores can be retrieved from the

lower and upper Messinia plain, which should cover the

last ca 6000 years. This is important to examine

whether the water level changes in Agios Floros are

related to local hydrological changes or represent

regional events. The latter is the most possible scenario

as indicated by other records in this plain. Thereafter,

similar studies covering the period between 6000 and

5000 cal BP could be performed in the Gialova Lagoon

and the Lake Lerna to examine the potential relation of

these events with the regional climate variability.

Although climate records are increasingly available

from the Peloponnese, there are still large gaps in the

spatial coverage. This holds especially true for the

eastern Peloponnese where the Lake Lerna record is the

only available paleoclimatic study in this area. The

abundant availability of wetland and lakes on the

Peloponnese indicates that there is potential to find

additional places, to increase the spatial coverage and to

achieve a better understanding of past climate

variability. Some suitable sites for future investigations

have already identified within the context of this PhD

project. These sites have similar settings as the Gialova

Lagoon, Lake Lerna and the Agios Floros fen and are

located in different climatic zones of the peninsula; the

Lake Taka, central Peloponnese, the Evrotas plain, SE

Peloponnese and Lake Stymphalia, NE Peloponnese.

Paleoclimate proxies and climate modeling can

provide complementary sources of information on past

climate changes. However, studies of paleoclimate

modeling have not been performed in the Peloponnese

despite the availability of proxy records. Therefore,

there is a great need to integrate the available records

with climate modeling to improve the understanding of

climate dynamics and to make better predictions of

future climate changes in the Eastern Mediterranean.

Finally, the results from this approach can be integrated

with archaeological findings, to improve our knowledge

of the impacts of past climate variability on former

human societies in this archaeologically rich region.

13. Financial supports

This PhD project was financed by the Swedish

Research Council (grant number 621-2012-4344; P.I.

Karin Holmgren) and is a part of the Navarino

Environmental Observatory (NEO) collaboration

between Stockholm University, the Academy of Athens

and TEMES S.A., Greece. Analytical work and travels

were further financed by: the Bolin Centre for climate

research and the project Domesticated Landscapes of

the Peloponnese (DoLP), Uppsala University with

funding from the Swedish Research Council (grant

number 421-2014-1181) and the Royal Swedish

Academy of Letters, History and Antiquities. Funds for

travels and conferences were further provided by the

Scholarship Foundation "Penelope Katsea - Spandou".

14. Acknowledgements

First and foremost, I would like to thank my supervisor,

Elin Norström, and my co-supervisor, Karin Holmgren,

who introduced me to this project and gave me the

opportunity to contribute to this field of natural science

in which I have a keen interest. Special thanks to Elin

Norström for constant support, inspiration and fruitful

discussions. I would like to thank my supervisor, Stefan

Wastegård, who provided me further support and trust.

I am grateful to my co-supervisor, Jan Risberg, for

valuable support and fruitful discussions throughout the

course of my studies. I am thankful to my co-

supervisor, Rienk Smittenberg, for his help with organic

geochemistry. I would like to thank Karin Helmens for

her support and fruitful discussions during my studies.

I am thankful to the 38th Ephorate of Prehistoric

and Classical Antiquities, Ministry of Culture and

Sports and the 26th Ephorate of Byzantine Antiquities,

Ministry of Culture and Sports for issuing permissions

to perform coring at the Gialova Lagoon and Agios

Floros. I would also like to thank the Ephorate of

Antiquities of Argolida for kindly giving the permission

to carry out coring at the Lake Lerna and the Swedish

Institute at Athens for help with these preparations.

I am grateful to the present, and former, station

managers of NEO station, Giorgos Maneas and Nikos

Kalivitis, for assisting with the field work planning and

performance in Agios Floros and Gialova Lagoon. I

would like to express my gratitude to Nikos Zacharias

for his hospitality in the laboratory of Archaeometry at

the University of the Peloponnese. Special thanks to

Pavlos Avramidis for his hospitality in the University of

Patras and for our collaboration all these years.

I would like to thank everyone who offered their

time to help with analytical work. I am thankful to

Malin Kylander, who helped me with the XRF analysis.

I would like to acknowledge Klara Hajnal for assistance

with extracting n-alkanes from the Lerna samples and

preparing the Lerna samples for bulk isotope analysis.

Special thanks to Anna Hägglund for assistance with

operating the GC-IRMS, and Heike Siegmund for

assistance with bulk isotope analysis. I am thankful to

Marianne Ahlbom for helping out with the performance

of the SEM analysis and also to Mats Regnell for

helping out with the identification of macrofossils.

I am grateful to the Domesticated Landscapes

group in Uppsala University, Erika Weiberg, Anton

Bonnier and Martin Finné for organizing all these

conferences and workshops and providing knowledge

about human-environment interaction in the

Peloponnese. Special thanks to Martin Finné for

inspiring discussion and comments on the manuscripts.

I would also like to thank a number of former

students and colleagues for their assistance in the lab

and field work. Thanks to Erika Modig and Helene

Sunmark for helping out with the performance of

fieldwork in Lake Lerna. Thanks to Lucas Ageby for

assisting with the construction of precipitation map of

the Peloponnese and the Gialova topographical map.

39

Thanks to Nichola Strandberg for helping out with the

examination of Gialova and Lerna cores for seeds.

I would like to express my gratitude to all technical

and administrative staff at the department of Physical

Geography, Stockholm University, for their constant

support. Special thanks to all my fellow PhD

candidates, former and current. It has been great and

very inspiring to share these years with you having

great dinners and fun. Eva Rocha, Charlotta Högberg,

Simon Larsson, Lindsey Higgins, Anna Plikk, Sandra

Sitoe. I am thankful to the Climate and Quaternary unit

for the nice excursion and moments in the Peloponnese.

Last but not least, I would like to thank my family, my

wife and all my friends. Thanks for being supportive

and for encouraging me during the years of my studies.

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