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Title: Potrok Aike Maar Lake Sediment Archive Drilling Project (PASADO)

Proponent(s): Bernd Zolitschka, Flavio Anselmetti, Daniel Ariztegui, Ray Bradley, Laurie Brown, Hugo Corbella, Helga De Wall, Pierre Francus, Andreas Luecke, Nora Maidana, Christian Ohlendorf, Frank Schaebitz, Stefan Wastegard

Keywords: (5 or less)

Southern Hemispheric westerlies, quantitative climate reconstruction, atmospheric dust, volcanic activity, maar formation, climate modelling

Location: Santa Cruz, Argentina

Contact Information: Contact Person: Bernd Zolitschka

Department: GEOPOLAR, Institute of Geography Organization: University of Bremen

Address: Celsiusstr. FVG-M, D-28359 Bremen, Germany Tel.: +49-421-218-2158 Fax: +49-421-218-9658

E-mail: [email protected] to post abstract on ICDP Web site: X Yes No

Abstract: (400 words or less) We propose to recover long sediment cores from Laguna Potrok Aike, a 770 ka old maar lake in the dry steppe of southern Patagonia (Province of Santa Cruz, Argentina). Seismic surveys demonstrate that ~400 m of pelagic sediments were deposited in the lake centre underlain by a yet unknown thickness of volcaniclastic breccias. Based on this seismic data, three primary and three alternative drilling sites were selected: (1) from the deepest part to obtain a continuous and high-resolution record of climatic and environmental changes and to unveil the phreatomagmatic history including more precise age constrains for the maar-diatreme formation from the volcaniclastic sediments below, (2) from a subaquatic lake level terrace at 35 m water depth to constrain the range of lake level variations and (3) from an angle hole passing through lacustrine sediments and the crater wall into the molasse-type basement rocks to study the impact of explosive volcanism, post-eruptive structural evolution and early processes of sedimentation in a relatively young maar-diatreme structure. Within the framework of an international and interdisciplinary scientific approach the recovered sediments will be used to test hypotheses related to this two broad themes:

• High-resolution quantitative climate and environmental reconstructions from orbital and suborbital (multimillennial) down to decadal timescales supported by multiple dating (e.g. 14C, OSL, Ar/Ar) and stratigraphic correlation (e.g. pollen, tephra, paleomagnetics) with emphasis on marine – ice core – terrestrial linkages and incorporation of results from GCM climate simulations;

• Detailed analyses of volcanic rocks and sediments provide insights into processes related to phreatomagmatic explosions and early sedimention in a mid-Pleistocene maar lake. Never before the entire lacustrine sediment record has been recoverd and underlying volcaniclastic sediments have been drilled and investigated in a young maar-diatreme structure.

An international team of scientists has been attracted to cooperate in the framework of PASADO to develop a comprehensive environmental, climatic and volcanological data set. Proposed science management and drilling operation plans have the objective to achieve all necessary technical and scientific needs to make PASADO internationally successful.

mailto:[email protected]

PASADO – Full ICDP Drilling Proposal B

Scientific Objectives: (250 words or less) Scientific deep drilling: The main goal of PASADO is to recover long, undisturbed and continuous lacustrine and volcaniclastic sediments from Laguna Potrok Aike as the basis for the following scientific objectives. Quantitative climate and environmental reconstructions: On orbital to decadal timescales a variety of multidisciplinary analytical methods will be applied to reach these scientific goals:

• Multiple dating to provide a sound timeframe for all analyses using 14C, OSL, Ar/Ar, tephrochronology, paleomagnetics

• High-resolution quantitative reconstruction of temperature, precipitation and hydrological variations based on chironomids, pollen, stable isotopes, inorganic carbon and biomarkers;

• Quantitative reconstruction of terrestrial vegetation and fire history applying pollen and charcoal;

• Development of high-resolution dust storm and volcanic tephra records based on mineralogical and geochemical fingerprints;

• Reconstruction of a paleosecular variation record of the Earth’s magnetic field; • Establishing marine – ice core – terrestrial linkages focusing on magnitude and abruptness of

glacial/interglacial transitions and periodicities during glacials and interglacials; • Evaluation of proxy-based hypotheses with GCM climate simulations to establish mechanistic

links between climate variability and forcing factors. Questions relate to (1) latitudinal shifts in the position of Southern Hemispheric westerlies, (2) recurrence patterns of synoptic-scale phenomena like polar outbreaks, (3) the role of ice sheets, oceanic and atmospheric circulation on climate change.

Understanding the phreatomagmatic history: Analysis of volcanic rocks and accidental clasts will provide a unique dataset to better understand the geometry and structure of maar-diatrems in soft-rock environments. This includes:

• Processes related to phreatomagmatic maar explosions; • Investigation of early sedimention in a maar lake; • Post-sedimentation and compaction history in Quaternary maar sediments.

Summary of Support Requested from ICDP

Requested

ICDP funds: (in US$)

1.382.000 US $

Estimated Total Project Budget (ICDP funds plus other sources):

2.004.195 US $

Planned Start:

Mobilisation in either Jan. 2008 or Jan. 2009

Estimated Duration in Month (On-site operations only):

3 months

Requested Operational

Support:

Drill Engineering (Please contact ICDPs Operational Support Group if required)

Downhole Logging (Please contact ICDPs OSG if required)

Field Lab Equipment (Please contact ICDPs OSG if required)

25,120 US$

Training Course (Please contact ICDPs OSG if required)

4,820 US$

Details such as a Budget Plan, Management Plan, and Drilling Plan to be provided as attachment to the Proposal. OSG contact: U. Harms ([email protected]), Phone: +49 331 288 1085

mailto:[email protected]

Potrok Aike Maar Lake Sediment Archive Drilling Project (PASADO)

a proposal submitted to the

International Continental Scientific Drilling Program (ICDP) Attn: Dr. Uli Harms

GeoForschungsZentrum Potsdam D-14473 Potsdam, Germany

Principal Investigators: Bernd Zolitschka, University of Bremen, Germany, [email protected]

Flavio S. Anselmetti, ETH-Zurich, Switzerland, [email protected]

Daniel Ariztegui, University of Geneva, Switzerland, [email protected]

Raymond S. Bradley, University of Massachusetts, USA, [email protected]

Laurie Brown, University of Massachusetts, USA, [email protected]

Hugo Corbella, Universidad Nacional de la Patagonia Austral, Río Gallegos and Museo

Argentino de Ciencias Naturales, Buenos Aires, Argentina, [email protected]

Helga De Wall, University of Wuerzburg, Germany, [email protected]

Pierre Francus, Institut National de la Recherche Scientifique Quebec, Canada,

[email protected]

Andreas Luecke, Research Centre Juelich, Germany, [email protected]

Nora I. Maidana, University of Buenos Aires, Argentina, [email protected]

Christian Ohlendorf, University of Bremen, Germany, [email protected]

Frank Schaebitz, University of Cologne, Germany, [email protected]

Stefan Wastegard, University of Stockholm, Sweden, [email protected]

PASADO – ICDP Full Drilling Proposal IV

Table of contents

1. Introduction ................................................................................................................ 1 2. Geology of the study area.......................................................................................... 2 3. Relevant previous work.............................................................................................. 4

3.1 Meteorological data ..................................................................................... 4 3.2 Limnology .................................................................................................... 5 3.3 Process studies ........................................................................................... 5 3.4 Seismic investigations ................................................................................. 7 3.5 Sediments.................................................................................................. 10 3.6 Paleoclimatic and environmental reconstruction ....................................... 11 3.7 Climate modelling ...................................................................................... 14

4. Importance of the study area ................................................................................... 15 5. Scientific motivation and goals of the drilling project................................................ 16 6. Proposed work ......................................................................................................... 18

6.1 Site selection and drilling strategy ............................................................. 18 6.2 Site survey information .............................................................................. 19 6.3 Geophysical downhole logging and log interpretation ............................... 20 6.4 Initial field-based investigations ................................................................. 21 6.5 Core storage, archiving and further lab-based processing ........................ 22

7. Expected scientific and societal benefits of the proposed work ............................... 24 8. Project management ................................................................................................ 24 9. International science team ....................................................................................... 26 10. Time table ................................................................................................................ 28 11. References............................................................................................................... 28

Appendices A1. Seismic stratigraphy and interpretation .................................................................... 32 A1.1 Aims........................................................................................................... 32 A1.2 Seismic methods ....................................................................................... 32 A1.3 Results....................................................................................................... 34 A1.3.1 Morphobathymetry..................................................................................... 34 A1.3.2 Seismic facies and seismic stratigraphy .................................................... 34 A1.3.3 Seismic stratigraphic interpretation of Unit I and implications for environmental history................................................................................. 41 A1.3.4 Maar geometry and anticipated deeper strata ........................................... 45 A1.3.5 References ................................................................................................ 45 A2. Seismic sections of proposed drill sites ................................................................... 47 A2.1 Maps .......................................................................................................... 47 A2.2 Seismic sections ........................................................................................ 48 A3. Permitting and environmental issues........................................................................ 54 A4. Education and outreach............................................................................................ 54 A5. Detailed budget ........................................................................................................ 55 A6. CVs of principal investigators ................................................................................... 61 A7. Relationship to other international geoscientific programmes .................................. 74 A8. Letters of support...................................................................................................... 75

PASADO – Full ICDP Drilling Proposal 1

1. Introduction We have recently identified the 100 m deep and 770 ka old maar lake Laguna Potrok Aike (52°S, 70°W; 113 m a.s.l.) in southern Patagonia (Argentina) as a potential ICDP drilling target and request funds for drilling operations in Argentina (Figs. 1, 2). The location of Laguna Potrok Aike is of global geological significance and potentially the only site that can provide a continuous and high-resolution terrestrial sediment record over several glacial cycles for South American mid-latitudes. The area is extremely sensitive to climatic changes and an ideal continental counterpart of marine records from the Atlantic and Pacific Oceans for a comprehensive understanding of the past climate system. Thus PASADO tackles a problem of global significance at a location of paramount importance, i.e. a „world-class“ geologic site. After the international ICDP workshop “PASADO” was carried out in March 2006 in Río Gallegos (Argentina), a broad international collaboration started and the best possible science team grew together with the aim to pool financial and technological resources to carry out the deep drilling with the GLAD800 coring system at Laguna Potrok Aike in close cooperation with DOSECC.

Fig. 1: Map of South America and satellite image of southern Patagonia with the maar lake Laguna Potrok Aike, some other lakes and the City of Río Gallegos indicated.

The “Potrok Aike Maar Lake Sediment Archive Drilling Project” (PASADO) plans to continue the incentive of ICDP in a sense that in addition to tropical lake coring activities also non-tropical sites are considered. However, all outer tropical sites are from the northern hemisphere. To improve our understanding of global climate dynamics PASADO will be the first location from the non-tropical southern hemisphere to be drilled within the framework of the ICDP.

A sound basis for PASADO was formed by seismic surveys and multidisciplinary reconstructions based on 1 m gravity and 19 m piston cores. Data from four seismic surveys indicate a funnel shape structure consistent with the interpretation of a maar-diatreme setting. The thickness of lake sediments exceeds 400 m. These data clearly make Laguna Potrok Aike a well-suited site for terrestrial climate reconstructions of the Southern Hemisphere. So far, just a few shallow drillings into maar-diatreme structures have been performed. All of them, except for kimberlite diatremes, are in Tertiary volcanic fields in basement-type wall rocks (e.g. Schulz et al., 2005) and so far there is a lack of information about the geometry of maar-diatremes in sedimentary and soft-rock settings. The geophysical survey in combination with the drillings at Laguna Potrok Aike will give important insights into the internal structure of maar-diatremes with relevance for their potential as sediment-traps. Bouguer anomalies of Quaternary maar structures are distinctly different from those of Tertiary maars (Büchel et al., 1987) and highlight the more mature stage of compaction in older maar sediments.

PASADO addresses several challenging issues of geoscientific and socioeconomic relevance related to Earth history, global environment and climate change, to volcanic


systems and to sedimentary basins as included in ICDP’s scientific themes. Research topics comprise quantitative climatic and environmental reconstruction, paleosecular variation of the Earth's magnetic field, natural hazards (fire history, history of volcanic activity including tephra fallout, dust deposition) and volcanic systems (evolution of phreatomagmatic craters, history of volcanic activity) for the last glacial to interglacial cycles. Moreover, from the beginning this project will include climate modelling components. Obtained reconstructions of climate variability will be compared statistically with the output of Global Circulation Model (GCM) simulations to improve our understanding of forcing mechanisms of the global climate system.

Fig. 2: Bathymetric map of Laguna Potrok Aike. Please note the Holocene lake level low stand (submerged terrace level at ca -35 m in dark green), young fluvial and lacustrine deposits (grey), the 1,19 Ma old basalt flow (red), the tephra deposits (pink), the moraine till (yellow), outcrops of Santa Cruz Formation (orange), the multi-channel seismic lines and the planned ICDP drill sites.

2. Geology of the study area The study area is located in the Pliocene to late Quaternary Pali Aike Volcanic Field (Fig. 3) a northwest-southeast oriented tectono-volcanic belt about 50 km wide and more than 150 km long. This back arc volcanic area (Mazzarini & D'Orazio, 2003) is situated in the Magellan Basin 80 km west of the city of Río Gallegos, 70 km north of the Strait of Magellan and about 100 km east of the Andean volcanic arc. Petrologically, the Pali Aike Volcanic Field consists of alkali-olivine basalts with an age range from 3.8 Ma (Pliocene) in the western part towards 0.01 Ma (Holocene) closer to the Atlantic Ocean (Fig. 3). Along fissure related eruptions, cinder cones, lava domes and about 100 maars (Ø 500 to 4000 m) have been formed.


Fig. 3: Map of the Pali Aike Volcanic Field with ages of Pliocene to late Quaternary back arc volcanism and position of mid-Pleistocene terminal moraines (Corbella, 2002; Zolitschka et al., 2006a).

The oldest outcropping geological strata in the immediate study area are Lower Miocene fine-grained molasse-type fluvial sediments of the Santa Cruz Formation (Fig. 2). During the Plio-Pleistocene, the investigated area south of the river Río Gallegos was covered by glaciers that originated from the Magellan Strait, Seno Skyring and Seno Otway (Fig. 3). Fluvioglacial deposits (Patagonian Gravel Formation) and moraine tills today form the surface of the southern Patagonian Plains. Glaciations occurred between 3.5 and 1.0 Ma. However, evidences and dating are poor (Rabassa & Clapperton, 1990; Zolitschka et al., 2006b).

Laguna Potrok Aike is a 100 m deep maar lake with a diameter of 3.5 km (Fig. 2). The entire depression has a diameter of about 5 km. At the southwestern crater rim a cinder cone with a well-developed basaltic lava flow which was Ar/Ar-dated to 1.19 ± 0.02 Ma is visible (Fig. 2; Zolitschka et al., 2006b). Both are covered with moraine till (Fig. 2). The lava flow never entered the lake and was not related to the formation of the maar. Glacial sediments and related terminal moraines ca 10 km south of Laguna Potrok Aike must be older than the maar (Fig. 3).

The tephra deposits at the lee-side of Laguna Potrok Aike (Fig. 2) are composed of volcanic fragments (juvenile and non-juvenile glass, lapilli and clasts) and accidental lithics. The common bed forms associated with base surge deposition are all indicating a typical phreatomagmatic explosive event in generating the Potrok Aike maar and its pyroclastic succession. Silt fragments and quartz grains derived from disrupted crystalline gravels as well as siliciclastic grains from alluvial deposits are found as accidental clasts. This suggests that the phreatomagmatic eruption not only occurred in the inter-basalt layer ground water table (e.g. pure water recharge), but either surface aquifers (e.g. fluvial or glaciofluvial systems with sand deposition) or interbedded water-saturated sand/silt/fine gravel layers provided water for the phreatomagmatic explosion.

Ar/Ar-dating of glass fragments (0.77 ± 0.24 Ma, Zolitschka et al., 2006b) reflects the heterogeneity of volcanic fragments in pyroclastic deposits. For more precise age determinations of the diatreme formation a distinction of non-juvenile volcanic fragments from disrupted co-magmatic dyke and sill or older lava flow fragments will be crucial.


Generally, a maar-diatreme structure is formed by a shallow explosive eruption caused by the contact of rising magma with groundwater. Shock waves cause a fragmentation of the wall rocks and due to ejection of the magmatic (juvenile) clasts mixed with wallrock clasts a cone-shaped diatreme with a crater rim is formed.

The size of the depression (Ø 5 km) or the lake (Ø 3.5 km) as observed at Potrok Aike today are very likely the result of wave erosion at the lake shore which is developed in soft sedimentary rocks. This explanation has been used for the four large Espenberg Maars in Alaska (Ø 4-7 km) which are developed in Pleistocene sediments (Beget et al., 1996). Reflection seismic revealed that this assumption seems to be correct also for Laguna Potrok Aike (Fig. A13; Gebhardt, 2006, pers. comm.). Here a diameter of only 2400 m has been determined for the initial maar-diatreme structure which seems to have the shape of a champaign glass. However, this diameter still is larger than the diameters of other maar-diatremes which are in the range of 10 to 1500 m and have diameter to depth ratios between 1:1 and 1:2.5 (Lorenz, 2003). The larger diameter can be a result of repeated phreatomagmatic explosions with downward migrating locus of thermohydraulic explosion, a consequence of the soft substrate environment or a combination of both.

3. Relevant previous work This proposal is based on two interdisciplinary projects in the framework of the German Climate Research Programme (DEKLIM) called “South American Lake Sediment Archives and Modelling” (SALSA) and “Transient simulation of the middle Holocene with a coupled atmosphere-ocean general circulation model” (MIDHOL). Moreover, four seismic surveys have been carried out within the DFG-funded project “Pre-site survey for potential new ICDP sites in southern Patagonia, Argentina” (POTROK) which is related to the DFG Priority Programme “ICDP”. This research had and still has a strong educational component with five Ph.D. theses (one finalised and four ongoing), two diploma and one state examination thesis. 3.1 Meteorological data The eastern part of southern Patagonia is a semiarid cool semidesert with steppe vegetation lacking any well-defined rainy season. A strong precipitation gradient exists between the west and the east coast of South America caused by the topography of the continent. The Southern Hemispheric westerlies (SHW) transport humid air from the Pacific Ocean to the Andes leading to annual precipitation sums of 4000-6000 mm along the west coast (Weischet, 1996). In the rain shadow east of the Cordillera, precipitation decreases to <400 mm and in the Pali Aike Volcanic Field even to <300 mm (Gonzalez & Rial, 2004). At the Potrok Aike meteorological station occasionally values of only 150 mm have been observed (Zolitschka et al., 2006b).

The SHW across Patagonia are characterized by high wind speeds with mean annual values of 7.4 ms-1 at Río Gallegos and maxima during summer. Wind direction is primarily from the west shifting occasionally to NW and SW (Weischet, 1996; Baruth et al., 1998). The instrumental meteorological record of the Río Gallegos weather station exists since 1931 but is rather fragmentary. It shows an annual mean precipitation sum of 250 mm and a mean annual temperature of 7.4°C with a July (winter) minimum of +1.0°C and a January (summer) maximum of 13.0°C. Both mean annual temperature and annual precipitation sum for the Potrok Aike meteorological station (990 m distance to the lake and run by INTA since January 1999) are 30-40% lower compared to the Río Gallegos weather station near the coast (Zolitschka et al., 2006b). While the differences in temperature can be explained by the increasing degree of continentality towards the west, the discrepancy in precipitation points towards an eastern source region for rainfall events that may be related to polar outbreaks. This assumption has been confirmed by statistical analysis of Potrok Aike meteorological data demonstrating that most precipitation is brought in by air masses from the east (Mayr et al., 2007b). Precipitation is thus an indicator for the strength of SHW and links hydrological data to the regional synoptic situation and to expected latitudinal shifts of SHW.


3.2. Limnology Laguna Potrok Aike is a 100 m deep maar lake with a surface area of 7.58 km² and one episodic inflow at its western and several episodic gullies at the eastern shore (Fig. 2). The lake is mostly fed by groundwater and currently has no surface outflow. As a closed lake system it reacts very sensitively to hydrological variations. This is evidenced by a multitude of surficial and submerged lake level terraces (Haberzettl et al., 2005). Morphometric data reveal an almost circular shape of the lake while the topography suggests a significant influence of the catchment area (estimated to ca 200 km²) on the lake system. Therefore, a thick sedimentary infill must be expected. Despite the large catchment area the maximum water depth still is 100 m which points to an enormous initial crater depth. Bathymetry (Fig. 2) reveals an almost flat and pot-shaped morphology of the lake floor typical for maar lakes. However, water profile data show that there is almost no stratification of the water column under present-day conditions (Fig. 4). This is due to strong winds that enforce polymictic conditions and hardly allow the formation of a thermally stratified water body during southern summers.

Fig. 4: High resolution water temperature data (thermo isopleths) recorded with 6 hr resolution by 7 thermistors attached to a mooring at the deepest part of Laguna Potrok Aike (Zolitschka et al., 2006b).

With regard to the ionic composition, the water of Laguna Potrok Aike is dominated by chloride and sodium followed by magnesium, potassium, calcium and sulphate at a pH between 8.7 and 9. This is supported by high electric conductivities between 2970 and 3110 µS cm-1 for the years 2002 to 2005. Laguna Potrok Aike is a subsaline lake with salinities ranging from 2.22 to 2.53 ppt. Nitrate concentrations were mostly below detection limit. Remarkably high are the total phosphorus (TP) concentrations in the surface water: 1300-3600 µg L-1 (Zolitschka et al., 2006b). Despite these high TP concentrations planktonic productivity is low which is also indicated by a secchi depth of 6.9 m. Elevated TP values are difficult to explain but might be related to groundwater inflow and regional geology. 3.3. Process studies Since the start of the SALSA project in the year 2002 we have established an extensive monitoring programme in and around Laguna Potrok Aike. This includes the meteorological station run by INTA in proximity to the lake. Moreover, thermistors are installed at various water depths attached to a mooring string in the lake to monitor seasonal temperature changes and mixing processes of the water body (Fig. 4). Attached to this mooring are also


sediment traps and a pressure sensor. The latter records lake level fluctuations continuously. This monitoring effort is important for an understanding of sediment forming processes because the terminal lake Laguna Potrok Aike is very sensitive to changes in the hydrological regime. Several terraces up to 25 m above and at least 35 m below present day lake level witness drastic lake level variations during the past. Studies of recent processes indicate that changes of the lake water volume lead to changes in the carbonate system (Haberzettl et al., 2005) and the oxygen isotopic composition of the lake water (Mayr et al., in prep.), which opens the possibility to trace such changes in the sedimentary record.

Meteorological together with stable isotope data, bathymetric information of the lake and calculations of the local radiation balance were used to perform hydrological balance calculations by combining an energy-budget with a bulk-transfer method (Brutseart, 1982; Penman, 1948). The obtained lake volume changes were translated into changes of the lake level between Jan. 2001 and Dec. 2004 (Ohlendorf et al., in prep.). For the time period Mar. 2003 until Dec. 2004 calculated lake level changes were compared to pressure sensor data (Fig. 5). The fact that calculated lake levels closely follow the measured ones indicates that lake level mainly is driven by the precipitation/evaporation ratio.

0.0

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0.40.6

0.8

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1.21.4

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Mar-03 May-03 Jul-03 Aug-03 Oct-03 Dec-03 Mar-04 May-04 Jul-04 Aug-04 Oct-04 Dec-04

Date

Lake

leve

l (m

)

LL measured, pressure sensor (m)LL calculated, ref. 14.03.03 (m)

Fig. 5: Lake level (LL) of Laguna Potrok Aike between March 2003 and Dec. 2004 as measured by a pressure sensor installed on a mooring string in 27.5 m water depth in comparison to a lake level curve that was calculated using an energy-budget/bulk-transfer approach (Ohlendorf et al., in prep.). The reference lake level is of March 14, 2003.

An analysis of the meteorological factors that contribute to the hydrological balance calculation reveals that together with precipitation, wind strength and wind direction exert an important influence on the hydrological balance of Laguna Potrok Aike. In particular, it is inferred that lake levels decrease during periods of persistently high wind speed (mostly from westerly directions) whereas they increase during periods with a more frequent occurrence of winds from easterly directions. Because the lake level, i.e. the lake water volume, controls the lake water carbonate system (Haberzettl et al., 2005), lake volume changes are archived in the sedimentary record through changes in the sediment carbonate content. In a first approximation the degree of supersaturation of the lake water with respect to calcite and thus the potential for lake internal calcite precipitation is a function of lake water volume, which was also confirmed by sediment trap studies. Hence, phases of high sedimentary calcite concentration represent periods with low lake levels. However, a quantification of this relationship is not admissible over long time intervals and we therefore attempt to combine this approach of water volume reconstruction with the stable isotope approach (Mayr et al., 2007a).

Already funded is a new project in the framework of the DFG priority programme “ICDP” that will start in February 2007 with the investigation of short sediment cores (46 gravity cores of up to 49 cm length). It is called “Analysis of sediment areal distribution in Laguna Potrok Aike” (ASADO). This proposal will bring forward our understanding of


processes controlling the spatial sediment distribution, geochemical sediment characteristics and nutrient availability in the modern maar lake. Moreover, the spatial distribution of pollen and diatoms as well as of the stable isotope signal will be investigated. In view of PASADO this knowledge is vital for a thorough understanding of the long sediment record to be drilled from the deep central lake basin.

Water chemistry and stable isotope data of surface waters from 23 lakes in the Patagonian steppe, but also from wells, springs, streams as well as precipitation, groundwater and atmospheric water vapour were sampled for isotope analyses (Mayr et al., 2007a; Zolitschka et al., 2006b). Such a stable isotope approach can be used for estimating the water balance of lakes. Obtained data imply that the isotopic composition of rainfall in south-eastern Patagonia is predominantly determined by precipitation amount and moisture source area. For the investigated area, the first meteoric water and evaporation lines in δ2H vs. δ18O space were derived (Fig. 6). For a better interpretation of biological proxies and to make available quantitative climate and environmental reconstructions, Argentine colleagues are developing training sets for diatoms, chironomids and pollen in order to develop transfer functions. These investigations are related to analyses of modern water, surface sediment and sediment or pollen trap samples from different seasons of Laguna Potrok Aike but also from a wide variety of other lakes in southern Patagonia.

Fig. 6: Stable isotope values of precipitation (Río Gallegos), surface water, groundwater and atmospheric vapour in δ2H vs. δ18O space (Mayr et al., 2007a). Precipitation data plot on the given Local Meteoric Water Line (LMWL), surface waters on a Local Evaporation Line (LEL).

3.4 Seismic investigations Four seismic surveys were carried out between 2003 and 2005 at Laguna Potrok Aike (Figs. 2, A2, A10) in order to reveal the general geometry of the maar lake and its bedrock and to characterize the internal structures and thicknesses of lacustrine sediments, their spatial distribution and possible lithologies. Different seismic methods were combined to obtain both high-resolution and deep penetration acoustic data which are critical in terms of finding ideal drill sites that provide undisturbed successions of lacustrine sediments. In early 2003 the subsurface of Laguna Potrok Aike was investigated with a high-resolution 3.5 kHz seismic surveying system. The second seismic campaign took place in Feb. 2004 and used two parallel 1 in3 airguns. To further increase seismic penetration, additional single-channel sparker data were acquired in Dec. 2004. Finally, in order to obtain a better insight into the general maar geometry and the deeper sedimentary layers, an additional seismic pre-site survey was carried out in March 2005 with a 40 in3 Mini-G airgun as acoustic source. The results of this deep seismic survey reveals an at least 400 m thick lacustrine sediment infill. The seismic stratigraphy and lithologic interpretations are summarized here. For detailed results including selected seismic lines please refer to chapters A1 and A2 in the appendix.


Two major seismic stratigraphic units (Units I and II) are identified in the seismic sections (Fig. 7). Unit I (with Subunits I-a to I-d) is of lacustrine origin, while Unit II consists of the surrounding bedrock that was fractured and ejected during the phreatomagmatic eruption forming the lake's depression. The lacustrine subsurface of the different morphobathymetric areas (lake shoulders, slopes, deep basin) cannot be physically connected, because the continuity of seismic reflections cannot be traced across the steep slopes.

Fig. 7: Interpreted line drawing of N-S multi-channel seismic reflection profile AWI-20058230 with proposed drill sites PTA2 and PTA3 (cf. Fig. 2). The diatreme flank (in yellow) is well-defined in the northern but not visible in the southern part of the lake.

Lacustrine Unit I (I-a to I-d): Subunits I-a and I-b can only be discerned on the lake shoulders, where they are separated by a major unconformity (Fig. A3). There, the upper ~5-10 m that define I-a consist of draping, slightly basinward dipping layers that terminate laterally when the slope becomes steeper. This unit conformably overlies an erosional unconformity, which persistently occurs around the entire lake truncating reflections of the underlying upper slope section (Fig. A4A). The consistent water depth of ~35 m that marks the outcrop of the erosional unconformity clearly points towards a significant lake level lowering to near that depth. During this phase, subaerial exposure led to the erosion of the upper slope sediments of Subunit I-b that have been deposited during previous lake level highstands. Because the depth of -35 m represents the deepest observed erosion, it is certain that the lake level did not fall beyond that depth and that at least during the more recent history represented by Subunits I-a and I-b, Laguna Potrok Aike never fell dry. Several lens-shaped convex upward features occurring on the unconformity mark paleoshorelines (Fig. A4B) formed during a stepwise transgression following the -35 m lowstand. Sediment cores have been taken across this unconformity (Fig. A7) and provide timing and the lithologic response to these lake level fluctuations.

In the central basin, all seismic reflections of the entire lacustrine infill (Unit I) bend slightly upward towards the edges of the basin indicating a bowl-shaped layer-cake sedimentary architecture that gradually becomes infilled without major unconformities. Here, Subunits I-a and I-b are merged into one Subunit I-ab, because neither an unconformity nor a detectable correlative conformity separates them. Acoustic velocities vary around 1550 m/s indicating unconsolidated lacustrine sediments. Within Subunit I-ab, seismic data indicates well-layered sediments that are interrupted in some areas by local mass flows (Figs. A3, A20) occurring at six stratigraphic levels (S0-S5). The undisturbed central part of Subunit I-ab has been recovered in a 19 m long core (Fig. A7). Interpreting the multi-channel airgun data, the deeper parts of Subunit I-ab extend down to 50-60 m below the central plain of the lake. Further mass movement deposits can be recognized mainly in the western, southern and eastern parts close to the steep diatreme flanks. Pelagic sedimentation dominates in the


central and northern parts. The boundary between I-ab and I-c is non-erosive with I-ab forming downlaps onto I-c from the eastern and western parts of the lake, pointing at a significant lake level change (Figs. A11, A12). Within this deeper section, I-c is a rather thin sedimentary package (approx. 20 m) that forms onlaps onto the underlying Subunit I-d in the eastern part of the lake, while this contact is conformal in north-south direction. Subunit I-c, probably deposited during a lowstand, has seismic velocities of ~1600 m/s characteristic for unconsolidated lacustrine mud. The boundary between I-c and I-d remains obscure in the western part of the central plain due to limited acoustic penetration. Similar to I-ab, I-d is characterized by well-stratified sediments intercalated with mass movement deposits mainly in the parts close to the diatreme flanks (Fig. A11). Its upper boundary is non-erosive; the lower boundary cannot be observed because it is masked by multiples in some areas and obscured due to limited acoustic penetration in others. This acoustic blanketing occurs mainly in the central and western part of the lake and might point to some free gas, but alternatively, could also be an indicator for thick coarse-grained deposits or tephra layers.

Bedrock (Unit II): The bedrock forming the steep diatreme flanks consists of the well-layered sandstones of the Santa Cruz Formation in the lake surroundings. The distinct facies change between the slightly dipping, bedded sandstone and the smaller scale layers of the lacustrine sediments resembles the facies changes in other maars (e.g. Messel Pit and Baruth Maar, Germany; Wiederhold, 2003; Schulz et al., 2005). The boundary between the diatreme flank and the lacustrine sediments is best visible in the northern and eastern part of the lake while it is much less pronounced in the western and southern parts where it is buried below thick packages of mass movement deposits (Figs. A11, A12). These packages tend to weaken the acoustic penetration making it difficult to distinguish correctly between lacustrine layers and bedrock bedding. Acoustic velocities of the sandstone bedrock are around 3000 m/s.

Maar geometry and anticipated deeper strata: The site survey data indicate that Laguna Potrok Aike is characterized by similar geometries like other investigated maars (Fig. A13), e.g. the Messel Pit and the Baruth Maar in Germany (Wiederhold, 2003; Schulz et al., 2005). Seismic surveys as well as deep drillings in both of these maars revealed a typical succession of maar-related lithologies followed by lacustrine sediments (Pirrung et al., 2003) so that we anticipate similar successions in Potrok Aike maar as well: (i) Lacustrine strata at the top are dominated by pelagic sedimentation in the upper layers and intercalated with or even dominated by mass movement deposits (debris flows and turbidites) in the deeper layers. The entire lacustrine sediment package has thicknesses of around 250 m in both cases with acoustic velocities of ~1500-1600 m/s in the pelagic sediments and up to 2400 m/s in the mass movement-dominated deposits (Wiederhold, 2003; Schulz et al., 2005; Goth et al., 2003). (ii) Lapilli tuffs and stratified collapse breccia that are formed immediately after the phreatomagmatic eruption as fallback and slope failure sediments. The boundary between these strata and the overlying lacustrine sediments is well defined by an abrupt increase to higher acoustic velocities of 3000 to 3500 m/s. (iii) Unstratified diatreme breccia with velocities in the range of 3000 to 3500 m/s, related to the phreatomagmatic eruption and subsequent collapse of the crater.

During preparation of a velocity model for stacking of the multi-channel data of Laguna Potrok Aike, observed velocities did not exceed 1800 m/s down to at least 600 ms twt in the central part of the lake, i.e. in the part between the steep diatreme flanks. Stacking and deconvolution using the derived velocity model, unfortunately, could not attenuate the multiples well enough to make deeper strata visible in the processed seismic sections. In any case, the lack of higher velocities points at lacustrine muds down at least 400 m below lake floor in the central part of the lake as the deeper, maar-related strata would require velocities as high as 3000 m/s according to the typical lithological success


3.5 Sediments A 19 m long piston core from the central 100 m deep basin of Laguna Potrok Aike provides a calibrated basal radiocarbon age of almost 16,000 cal. BP (Figs. 8, 9). In general, the sediment record consists of clayey and sandy silts becoming slightly coarser with depth (Fig. 8). Only tephra layers and reworked volcanic ashes comprise fine to medium sand. The sediment is minerogenic silt with mostly <4% and rarely up to 10% total organic carbon (Haberzettl et al., 2007a). The carbonate content can be as high as 33% (Figs. 10, 11: TIC x 8.33). The multi-channel seismic survey indicates a thickness of the lacustrine sediment sequence of ca 400 m. Based on the age-depth relationship established by Haberzettl et al. (2007a) for the sediment record from the centre of the lake (Fig. 9), two different estimations are possible for the entire sediment record that will be recovered with the GLAD800:

Fig. 8: Lithology of the composite sediment record from Laguna Potrok Aike (piston core PTA-03/12) including medians of calibrated radiocarbon dates (Haberzettl et al., 2007a).


Fig. 9: Age-depth model (Haberzettl et al., 2007a, modified) based on calibrated radiocarbon ages, volcanic ash layers and optically stimulated luminescence dating (OSL). • Assuming 400 m of continuous sedimentation and an onset of lacustrine deposition

shortly after formation of the maar around 770 ka, we estimate a linear sedimentation rate of 0.52 mm yr-1;

• If we estimate the onset of sedimentation by extrapolating the linear sedimentation rate of 1.05 mm yr-1 that was determined for the last 16,000 years to the entire record of 400 m, we yield a basal age of ca 380 ka. As we have no indications for erosional hiatuses in the deep lake basin due to desiccation, we assume that compaction, which has not been taken into consideration for this calculation, is the main reason for this underestimation. Another option is that sediment thickness could be more than 400 m.

Altogether, estimates demonstrate that the sedimentary record from Laguna Potrok Aike covers at least three and maybe up to seven glacial to interglacial cycles, perhaps even back to the Brunhes/Matuyama boundary and thus will be unique for extra-tropical South America.

High resolution seismic studies revealed an unconformity in a subaquatic lake level terrace of Laguna Potrok Aike. This unconformity in the terrace located approximately 35 m below the present lake surface can be traced all around the lake. It is characterized by 3-4 m of almost horizontally layered sediments above and sediments dipping towards the lake centre below. Piston cores recovered from such a site verify this unconformity. Sediments above the unconformity consist of dark brown to black silts, whereas below the unconformity greenish brown fine sands dominate (Haberzettl et al., 2007b). Dating confirms this unconformity and reveals a hiatus of almost 40,000 years with continuous deposition starting again around 7000 cal. BP (Haberzettl et al., 2007b). Recently, the oldest radiocarbon age of 44,800 BP was confirmed by an OSL age of 53 ka from the base of the record. All sedimentological data support the interpretation that the lake level was considerably lower than today before 7000 cal. BP which caused the presence of a hiatus with unknown duration in this shallow part of the lake. 3.6 Paleoclimatic and environmental reconstruction The 19 m long (Fig. 8) and multiple-dated (Fig. 9) piston core profile from Laguna Potrok Aike exhibits distinct changes in sedimentary parameters that indicate climatic and environmental variabilities. Monitoring data suggests that the content of total inorganic carbon (TIC) mirrors changes of the lake’s water volume and reflects variations in the


hydrological cycle. Thus it is possible to reconstruct hydrological variations for the last two millennia (Fig. 10) and for the entire Holocene and the Late-Glacial (Fig. 11). Recent studies of other lakes further to the northwest (Lago del Desierto, Laguna Chaltel, Laguna de las Vizcachas; all unpubl. own data) indicate that this is at least a regional signal caused either by latitudinal shifts or by intensity variations of the SHW.

Fig. 10: Total inorganic carbon (TIC) record as a proxy for lake level fluctuations reflecting hydrological variations during the last 1600 years based on a 1 m gravity core from Laguna Potrok Aike (Haberzettl et al., 2005).

Fig. 11: Total inorganic carbon (TIC) and Titanium (Ti) records for the late Weichselian and Holocene of Laguna Potrok Aike as indicators for lake level fluctuations (TIC) and detritic sediment input (Ti). Both proxies reflect wet conditions for the time prior to 13,000 cal. BP (the lake had an outflow) and moist conditions for the early Holocene (no outflow anymore), whereas the Late-Glacial and the Holocene since 8700 cal. BP are characterised by marked dry/moist cycles (Haberzettl et al., 2007a, modified).

These data demonstrate that the region experienced drastic environmental changes in

the past. The record from Laguna Potrok Aike suggests moist conditions during the Late-Glacial and the early Holocene (16,000-8700 cal. BP) interrupted by drier conditions before the beginning of the Holocene (13,200-11,400 cal. BP). Data also imply that this period was a major warm phase in south-eastern Patagonia approximately contemporaneous to the Younger Dryas chronozone in the Northern Hemisphere (12,700-11,500 cal. BP). The most drastic changes of the record start with the deposition of the Mt. Burney tephra generating intensified erosion. Thereafter, the lake level fell to its lowest Holocene position (8650-7300 cal. BP). After a transgression period the lake level was extremely variable. The last exceptionally high lake level is ascribed to the Little Ice Age (Fig. 10), which was the most


humid phase since the early Holocene (prior to 8650 cal. BP). This interpretation is supported by pollen and diatom analyses (Wille et al., 2007).

High-resolution analyses of allochthonous pollen (Andean forest taxa – AFT, i.e. mainly Nothofagus) deposited in Laguna Potrok Aike reflect the variability of zonal wind intensities during the Holocene. These indicators for the strength of SHW co-vary on centennial timescales with C/N ratios and Ti contents, interpreted as differential organic matter sources and minerogenic input to the sediment, respectively (Fig. 12). The correlations underline a linkage between hydrological variability and west wind variability in Extra-Andean Patagonia (Mayr et al., 2007b). When the SHW intensity was strong, more arid conditions prevailed (low Ti) and more littoral organic matter was deposited (higher C/N) due to lower lake levels. A shift to generally more intense SHW suggests intensification to modern wind conditions at that latitude around 9200 cal BP (Fig. 12). Accordingly, the period with most intense SHW was 8.7–7.4 ka cal BP coinciding with the suggested lowest Holocene lake level (Haberzettl et al., 2007a). During periods with weakened SHW, air masses from easterly directions reached Laguna Potrok Aike more frequently giving rise to enhanced precipitation (high Ti) and dominance of algal organic matter (low C/N) prevailing during periods of high lake levels. Hence, the coherence of Ti and C/N variations with the AFT record allows a detailed reconstruction of SHW intensity and its impact on the ecosystem (Mayr et al., 2007b).

Fig. 12: Andean forst taxa (AFT) pollen variations as AFT flux (logarithmic scale) and AFT index (a) compared to C/N ratios (b) and Ti contents (c). Interpretation of proxies to the right; OM: organic matter (Mayr et al., 2007b).

The record from Laguna Potrok Aike demonstrates that the SHW strength varied on centennial to multi-centennial time scales. Comparable quasi-millennial periodicities of climate proxies are well-known from Antarctic ice cores (Masson et al., 2000; Delmonte et al., 2005) suggesting changes in southern hemispheric atmospheric circulation as a fundamental control mechanism. Compared to other proxy records in the South American realm from continental (e.g. Jenny et al., 2003; Gilli et al., 2005) and marine (Lamy et al., 2001) sites, our record shows an earlier onset of intensified SHW in the Holocene. Data further suggest that SHW were much more variable during the Holocene than previously inferred from other records.


3.7 Climate modelling In the framework of the project MIDHOL the hydrological regime at Laguna Potrok Aike has been analyzed in terms of precipitation and its link to large-scale atmospheric circulation. Transient simulations were done in which a combination of orbital, solar and greenhouse gas forcing were used to drive the global coupled atmosphere-ocean model ECHO-G for the mid-Holocene (7000-4500 cal. BP). Results were compared to a quasi-equilibrium pre-industrial control simulation with constant conditions of 1750 AD.

The coarse horizontal resolution (approx. 300 x 300 km) of the GCM is of special concern for the complex topographic terrain over southern Patagonia. Thus the climate model output related to hydrological variables (precipitation, evaporation) could not directly be used for comparison with local conditions derived from sediment proxy data, i.e. lake level variations. For the mid-Holocene lake levels were reconstructed to have been lower compared to pre-industrial times (Haberzettl et al., 2007a).

To overcome the scale-mismatch between the large scales of the climate model and the local scale of the proxy data, a downscaling approach was applied to link the large-scale atmospheric circulation (LSC) with local precipitation. This approach includes two steps: First, a statistical downscaling model was calibrated and validated with observational meteorological data. Here statistical transfer functions have been setup between large-scale sea level pressure over southern South America and precipitation at Laguna Potrok Aike for the second half of the 20th century. In a second step these transfer functions have been applied to the simulated LSC of the ECHO-G model.

Fig. 13 left side: Time series of estimated precipitation for the orbital-forced simulation (ORB) based on simulated large scale circulation during the mid-Holocene at Laguna Potrok Aike for Dec.-Feb. (DJF, upper panel) and June-Aug. (JJA, lower panel). Dashed lines are the 95% confidence intervals related to the uncertainties of downscaling models. Note reduced precipitation during DJF and increased precipitation during JJA compared to pre-industrial times (CONPRE). Right side: Differences in vertical cross-sections of zonal winds along 70° W between the situation at 6000 cal. BP and pre-industrial times for DJF (upper panel) and JJA (lower panel). Note increased zonal winds over southern South America during DJF as opposed to reduced winds during JJA.


An advantage of the statistical downscaling model is the analysis of the driving mechanisms between LSC and precipitation. Specifically for the situation at Laguna Potrok Aike it was realised that increased westerly winds are associated with reduced precipitation and vice versa. However, as also shown by the downscaling model, this link is only moderate, because only 25% of the variability of precipitation at Laguna Potrok Aike can be explained by changes of LSC on a monthly basis.

The large-scale information of the climate model related to SHW was directly used for comparison with the large-scale hypothesis formulated on information derived from proxy data for the mid-Holocene. These hypotheses are related i) to a year-round northward position (Markgraf, 1993; Markgraf et al. 2003) of SHW and ii) to an increased seasonality (Schäbitz, 1999; Mancini et al., 2005) of SHW.

Results of the estimated precipitation based on the downscaling of the simulated LSC are given for southern summer (Dec.–Feb.: Fig. 13 upper panel) and winter (June–Aug.: Fig. 13 lower panel) for the period 7000–4500 cal. BP. In the right panel vertical cross-sections of differences of zonal winds along 70°W between 6000 cal. BP and pre-industrial times (AD 1750) are given for the same seasons.

During DJF slightly reduced precipitation is evident compared to pre-industrial times, whereas during JJA increased precipitation is observed. The annual precipitation difference (not shown) shows slightly increased precipitation and thus seems to be inconsistent with reconstructed lower lake levels at Laguna Potrok Aike. However, since precipitation cannot explain the full range of lake level changes, evaporation needs to be taken into account to compare modeling (downscaling) results and proxy reconstructions on a consistent basis.

An explanation for precipitation changes during the mid-Holocene are changes of zonal winds. Increased westerly winds at Laguna Potrok Aike are associated with reduced precipitation and vice versa. Here climate simulations indicate reduced westerly (zonal) winds during JJA and increased westerly winds during DJF over southern South America. The situation is different further to the north, where winds are increased during JJA and reduced during DJF. Therefore, simulations support the large-scale proxy hypothesis related to an increased seasonality of SHW during the mid-Holocene.

4. Importance of the study area In the southern hemisphere long, continuous and high resolution series of terrestrial paleoclimatic data are scarce and only slowly emerging, e.g. from New Zealand (Horrocks et al., 2005; Shulmeister et al., 2004; Turney et al., 2006). Such records are a key to a better evaluation of teleconnections and inter-hemispheric differences. In recent studies it emerged that for a proper understanding of the global climate system Southern Oceans play a key role (Kaiser et al., 2007, Knorr and Lohmann, 2003, White and Peterson, 1996). The most extreme oceanic character globally is encountered between 40°S and 60°S where 98% of water are juxtaposed to 2% of land: Patagonia and a few small islands. This region close to the Andean volcanic chain is subject to shifts in polar and mid-latitude pressure fields and precipitation regimes. It also is affected by the El Niño Southern Oscillation (ENSO) phenomenon (Ariztegui et al., 2007) and by the Antarctic Oscillation (AAO; Jones and Widmann, 2003). Patagonia thus can potentially provide unique terrestrial records of variations in (1) climate, (2) hydrology and (3) deposition of aeolian dust. Such records also may act as a cornerstone for palaeodata-model comparisons (Wagner et al., submitted.). Additionally, links can be established to ice cores from Antarctica and to marine records from the Southern Oceans where dust and tephra of Patagonian provenance have been detected (Basile et al., 1997, Diekmann et al., 2000, Narcisi et al., 2005).

For southernmost South America lake studies are still rare and extend in time not beyond the Late-Glacial. At Lago Cardiel a 3,5 kHz seismic survey together with 14C-dated sediment cores indicate that this 75 m deep lake contains only sediments spanning ~20,000 years and almost dried out around 13,000 cal. BP (Gilli et al., 2001, Gilli et al., 2005a, b; Markgraf et al., 2003). Similarly, investigations of lake sediment cores from the Gran Campo


Nevado area in Chile (53°S) provide records for Late-Glacial and Postglacial times (Kilian et al., 2000). Only for Laguna Potrok Aike a 16,000 year record with high temporal resolution (Haberzettl et al., 2007a) and a second record of lower resolution back to MIS 3 with a hiatus of unknown duration exists (Haberzettl et al., 2007b). Thus continuous records from southern South America that reach back far beyond the onset of the Late-Glacial are still missing.

In areas not scoured by young glaciations (Fig. 3), volcanic crater lakes are ideal for the recovery of long and continuous paleoenvironmental records. Their potential has been demonstrated for the West Eifel Volcanic Field, Germany (e.g. Negendank and Zolitschka, 1993; Zolitschka et al., 2000), for the Massif Central, France (e.g. Thouveny et al., 1994), for southern Italy (e.g. Allen et al., 1999; Guilizzoni and Oldfield, 1996; Zolitschka and Negendank, 1996), for China (e.g. Mingram et al., 2004a, b) and for New Zealand (e.g. Horrocks et al., 2005). Laguna Potrok Aike is the only lake in the Pali Aike Volcanic Field with a continuous sedimentary record potentially covering several glacial to interglacial cycles.

In addition to climatic and paleoenvironmental research related to its lacustrine deposits this maar opens yet another window for research: investigation into formation, structure and composition of a relatively young maar-diatreme structure. Scientific drilling was never before carried out into the deep diatreme underneath a modern maar lake. Studies of maar structures currently include only records from Tertiary dry maars (e.g. Pirrung et al., 2003; Schulz et al., 2005). However, a first comparison of the lithology of the scientific drilling into the Messel Pit, an Eocene maar structure in Germany, fits well with the deep seismic structure of Laguna Potrok Aike (Fig. A13). Altogether, the global importance of deep scientific drilling into the maar structure of Laguna Potrok Aike is based on two elements: • Quantitative climate reconstruction in combination with proxy-model intercomparison; • Investigation of the phreatomagmatic formation and early sedimentation of a young maar.

5. Scientific motivation and goals of the drilling project The proposed project PASADO is an interdisciplinary scientific deep drilling and analytical laboratory effort with wide international participation. Laguna Potrok Aike has been recognised as an outstanding geological site to study the continental climate and environment of South American mid-latitudes continuously and with high temporal resolution. The critical role of the Southern Hemisphere for climate reconstructions is generally accepted, but links between tropical and Antarctic climates at decadal to centennial timescales across different archives have yet to be established. Especially with terrestrial records an understanding of long-term environmental changes on the southern continents is still in its formative stages as proxy records are both spatially diffuse and temporally discontinuous. The increasing awareness of major inter- and intra-hemispheric disparities in the timing of climatic signals and forcing that influences land, ocean and ice core records underscores the need for the proposed integrated effort to explore the dynamics of the Southern Hemisphere climate system. Such a paleoclimatic record from diverse proxy sources provides a much wider range of realisations needed to describe and understand the full range of natural climate system behaviour. Moreover, for the first time, it will be possible to drill through the entire lacustrine sedimentary sequence and into the underlying volcaniclastic breccias to investigate the phreatomagmatic formation of a maar structure and to study the processes of early sedimentation in a maar.

With conventional coring equipment it was possible to obtain 19 m of sediment in 100 m of water depth covering the last 16,000 years. Now we are at a stage to implement another dimension to reach our goals and drill the entire sediment sequence of ca 400 m of lacustrine sediments plus ca 200 m penetration into the volcanic breccias underneath. To recover such a suite of long cores from Laguna Potrok Aike we have to use scientific drilling equipment (GLAD800) operated by DOSECC in the framework of the ICDP. Our well established local collaboration with INTA, UNPA and Capt. Moreteau and his crew will augment the process of drilling by e.g. providing logistical support and room for the field


laboratory, building the dock at the lake shore and running a vessel to shuttle the crew and to tow the drill rig.

Once sediment cores have been recovered, the drill holes will be analysed with an extensive down hole logging programme. Sediment cores themselves will be scanned on-site with a multi sensor core logger (MSCL) and archived following standard protocols. After shipping to Bremen, cores will be opened and analysed non-destructively. Only after this has been accomplished, discrete sampling will start including a wide range of internationally-based interdisciplinary analyses. Due to the unique geographic situation of Laguna Potrok Aike we envisage the following scientific goals for PASADO:

Quantitative climate and environmental reconsystructions: • Establish a chronology from orbital and suborbital (multimillennial) down to decadal

timescales supported by multiple dating (e.g. 14C, OSL, Ar/Ar) and stratigraphic correlation (e.g. pollen and paleomagnetic records);

• High-resolution quantitative reconstruction of temperature (based on chironomids and biomarkers) as well as precipitation and hydrological variations (based on total inorganic carbon, pollen and stable isotopes);

• High-resolution quantitative reconstruction of terrestrial vegetation (pollen) and fire history (charcoal);

• Development of records of dust storm events and volcanic eruptions based on their mineralogical and geochemical fingerprints;

• Reconstruction of paleosecular variation of the Earth’s magnetic field; • Establish marine – ice core – terrestrial linkages

o by developing models that allow to trace atmospheric dust from Patagonian sources to marine sediments (South Atlantic) and ice cores (Antarctica) and

o by comparing the PASADO data set with the high-resolution EPICA (2004) ice core record from Antarctica focusing (1) on the magnitude and abruptness of glacial/interglacial transitions and (2) on the periodicities and cycles during glacials and interglacials;

• Statistical comparison of PASADO data with climate simulations from GCMs to establish links between climate variability and climate forcing factors such as changes in the Earth’s orbit, solar output and greenhouse gas concentrations. Questions to be answered include: o Are latitudinal shifts in the position of the SHW reproducible? o Are synoptic-scale phenomena like polar outbreaks and their recurrence patterns

represented? o Can synchronous interhemispheric climatic linkages be detected to assess the role of

ice sheets, oceanic and atmospheric circulation and astronomic forcing on climate?

Phreatomagmatic history: • Processes related to phreatomagmatic maar explosions are investigated to

o reconstruct the geometry of diatreme structures in sedimentary host rocks (first opportunity to drill a maar structure in the framework of the ICDP) in order to establish the evolution of maar formation and to proof the models for maar diatrems;

o link internal processes (volcanism, tectonics) with external processes (glaciation); o obtain more precise age constraints on the formation of the maar and on the last

glaciation at 52°S; • Investigation of early sedimentation in a young (~770 ka) maar lake; • Contribution to the understanding of post-sedimentation and compaction history of

Quaternary maar sediments.

To achieve these goals scientifically, we apply for an accompanying science programme including down hole logging and logging of all sediment cores in the field with a MSCL. Additionally, laboratory-based analyses will be carried out in subsequent international research projects that will make intensive use of the recovered sediment cores. To achieve these goals technically, we apply for a scientific drilling with the GLAD800 system:


• To drill the complete lacustrine sediment infill (ca 400 m) in triplicate from the centre of the lake,

• To drill the lacustrine sediment infill (ca 50 m) in triplicate from a 35 m lake level terrace to better understand lake level fluctuations,

• To drill into phreatomagmatic breccias and the maar diatreme at the central lake drilling site from ca 400 to 600 m sediment depth and

• To drill from the lake with an angle hole through the crater wall and into the basement rocks.

6. Proposed work 6.1 Site selection and drilling strategy The highest priority drilling site is located in the deep central basin (sites 2, 5: Fig. 2). Here seismic data indicate deepest penetration of at least 400 m and this is also the site where hiatuses related to lake level fluctuations are not expected. Therefore, this site offers best conditions to recover a continuous and high resolution sediment record necessary to reach all scientific objectives. Marginal to the deep central plain slump deposits have been detected seismically. These areas will be avoided for drilling. Coring transects at Laguna Potrok Aike is not feasible because basin flanks are rather steep and erosion is likely. Only the circum-lacustrine lake level terrace at 35 m water depth provides another option for drilling (sites 1, 4: Fig. 2). Here an erosional hiatus has already been detected (Haberzettl et al., 2007b) and we expect a discontinuous record. Linked to the profundal sediment record this site will give important additional information about hydrological variations and thus improves the overall interpretation. This location is scheduled to become the first drill site because the order of drilling will be from shallow to deep. The third and last drilling site will be near the northern end of the lake at 90 m water depth where an angle hole will be drilled through the crater wall and into the basement rock (Lower Miocene fluvial sandstones, Santa Cruz Formation) to investigate the transition zone that was formed during maar eruption (sites 3, 6: Fig. 2). This drill site is dedicated for volcanological investigations. Similarly, after having penetrated into 400 m of lake sediments in the central basin (sites PTA08-2/5: Tabs. 1, 2), drilling continues into volcanic breccias (sites PTA08-2C/5C: Tabs. 1, 2).

Tab. 1: Proposed primary drilling sites at Laguna Potrok Aike. Drill site PTA

Latitude (°S)

Longitude (°W)

Water depth

(m)

Depth of penetra-tion (m)

Water depth + penetration

(m)

No. of holes

Total core recovery

(m)

Drilling days*

Logging days**

min-max 08-1 -51,9541 -70,3683 35 50 85 3 150 6 0.7-2.0 08-2 -51,9641 -70,3760 100 400 500 2 800 32 1.2-2.0 08-2C -51,9641 -70,3760 100 600 700 1 600 24 0.8-1.2 08-3 -51,9576 -70,3765 90 300 390 1 300 12 0.6-1.0 Total 7 1850 74 3.3-6.2 * Estimation of drilling days is based on 25 m per day. **Estimation of logging days is based on data of Tab. 3.

Tab. 2: Proposed alternate drilling sites at Laguna Potrok Aike. Drill site PTA

Latitude (°S)

Longitude (°W)

Water depth

(m)

Depth of penetra-tion (m)

Water depth + penetration

(m) No. of holes

Total core recovery

(m) Drilling days*

Logging days**

min-max 08-4 -51,9549 -70,3889 35 50 85 3 150 6 0.7-2.0

08-5 -51,9642 -70,3778 100 400 500 2 800 32 1.2-2.0

08-5C -51,9642 -70,3778 100 600 700 1 600 24 0.8-1.2

08-6 -51,9569 -70,3786 90 300 390 1 300 12 0.6-1.0

Total 7 1850 74 3.3-6.2

* Estimation of drilling days is based on 25 m per day. **Estimation of logging days is based on data of Tab. 3.


Altogether, we propose to drill three sites (Fig. 2, Tab. 1). Three alternate sites have been identified if a primary site has to be abandoned for technical, scientific or other unforeseeable reasons (Fig. 2, Tab. 2). Sediment cores for climatic and environmental studies will be recovered in triplicate to ensure a complete and overlapping sedimentary record. For volcanological investigations one hole per site is sufficient. We intend to almost exclusively use the hydraulic piston corer (HPC) for lacustrine sediments. However, near the transition to volcanic breccias and for the basement rocks of the angle hole the Extended Nose (EXN), Extended Core Bit (The Alien) or the Diamond Core Bit may come into action. 6.2 Site survey information The proposed drilling sites were determined based on bathymetric (Fig. 2) and seismic data (Figs. 7, A15-21). Penetration depths are listed in Tabs. 1 and 2. According to seismic profiles and recovered piston cores we expect the following lithologies: • Pelagic lake sediments: They are recognized on seismic data by a laterally-continuous,

reflective seismic facies and a “draping” geometry composed of variable amounts of authigenic and biogenic calcite, silt- to clay-sized clastics and organic matter. The relative percentages differ between lake level high- and lowstands. This sediment type has been continuously deposited and will be the prime target for climatic and environmental reconstructions (cf. Fig. 8).

• Volcanic ash layers: Tephra layers occur occasionally with a thickness ranging from less than 1 mm up to several cm and vary in grain size from silt to sand (cf. Fig. 8). They are very useful for core correlation and dating (tephrochronology) and can be distinguished on seismic data.

• Turbidites and slump deposits: Due to the distal position of all sediment cores recovered so far, classic turbidites related to flood-events have not been detected and are assumed to play no role for the proposed drilling sites. Slump deposits, however, are present due to the steep side walls of the lake basin and have been mapped in detail with seismic data. Thus, drilling sites will be positioned in areas where these units are absent. At greater sediment depths, where penetration of the seismic signal was insufficient to image the sediment geometry in detail, slump deposits may be more common as the basin gets narrower and steeper.

• Litoral lake sediments: At the 35 m lake level terrace we plan to penetrate through the paleoshoreline. Larger grain sizes like coarse silt and sand as well as reworked carbonaceous shells and plant macro fossils are likely. We do not expect that hard soil or desiccation horizons occur, as this was not the case in the cores we recovered with piston and gravity cores.

• Volcaniclastic breccias: Neither seismic nor former drilling operations penetrated deep enough to reach down to this sedimentary unit. We assume that sediments are comparable to investigated Tertiary dry maar records (Schulz et al., 2005). Following this approach, breccias may consist of a series of clastic units including (from top to bottom) debris flows, collapse breccias, lapilli tuff as well as stratified and unstratified diatreme breccias.

• Fluvial sandstones: Uplift of the Andes caused the formation of Lower Miocene fine-grained molasses-type fluvial sandstones of the Santa Cruz Formation. This rather soft sandstone is believed to compose the basement underneath Laguna Potrok Aike.

Potential sources of hazards during drilling operations are thought to be minimum. Indeed, the relatively minor penetration of the 3.5 kHz seismic system (Figs. A2, A7B) is not related to the presence of gas but rather to tephra layers that seem to absorb considerable acoustic energy. Weather should as well pose no significant hazard on drilling activities because the lake is relatively small (7.6 km2) and thus has only a small fetch even though wind speed can be significantly higher than 6 bft. Ideally, drilling should occur during summer. Weather conditions are mostly good, although wind strengths increase until noon and then start to decrease again. Precipitation is very low in general.


Logistically, trucks easily reach Laguna Potrok Aike. Paved roads exist from Buenos Aires (where the equipment has to be cleared through customs) to Río Gallegos (2639 km). Paved and dirt roads reach the lake from Río Gallegos (112 km), where trucks can almost drive to the lake shore. Only the last 50 m to the shore need to be levelled and supported. The lake itself has no harbour or any other facility. Therefore, a dock with electricity and lighting needs to be built. A catamaran, R/V “Lago Cardiel”, is already on the lake and will be available as a safety, shuttle and towing boat. 6.3 Geophysical downhole logging and log interpretation Borehole logging in lacustrine sediments is essential to obtain continuous in situ physical and chemical information around the borehole and to give an overview of the subsurface geology at the drill sites. Data sets obtained by wireline logging with slimhole tools provide the following information:

• True vertical depths, precise depth locations of the bottom hole, measurements of borehole dimensions and volume calculations provide a means for core re-orientation and are necessary for monitoring the drilling process.

• Precise core depths and corrections of core deformation resulting from the process of coring (stretching and compressing).

• Hole to hole correlation for multiple drill sites, detection of gaps in core recovery and determination of a continuous profile. A composite stratigraphy for each drill site based on triplicate coring will be established. Moreover, changes within overlapping core sections help to interpret the lateral (spatial) lithological variability if any.

• Characterisation of petrophysical properties of sedimentary rocks. These include sediment composition, textures and facies, rock magnetic properties and porosities and will be compared to later laboratory-based analyses on discrete sediment samples. Interpretation will be related to compaction and diagenetic characteristics, stratigraphy, unconformities and lithologic boundaries, identification of volcanic ash layers and sequence stratigraphy.

• Structural properties of drilled hard rock sections. The planned dipmeter, borehole televiewer (BHTV) and caliper measurements will be used to determine the predominant stress field. This can be used to achieve information, e.g. about volcanic processes during the development of Laguna Potrok Aike.

• Measurements of dip and orientation of sedimentary structures. • Construction of the “equivalent logging depth” which will be used in comparison with the

sediment core depth to correct the latter and to obtain the “true depth”. • Integration and calibration of seismic profiles and 3D modelling around boreholes. A

time/depth-calculation is needed to extrapolate the geological information of seismic profiles into lateral direction. This is done using the vertical seismic profile (VSP), which produces an exact velocity model.

Successful core recovery will depend strongly on good control of downhole conditions and borehole stability during coring. Therefore, in situ downhole measurements of e.g. borehole geometry and borehole dip are important to deal efficiently with potential drilling problems. Geophysical logs will be available on-site and provide all the necessary quick stratigraphic information.

All logging operations will be conducted with the equipment for geophysical measurements in small-scale drill holes available at the Leibniz Institute for Applied Geophysics (GGA) in Hannover (Wonik & Salge 2000; Wonik & Bücker 2000). Comparable slimhole tools have already been deployed successfully with the GLAD800 drilling platform during earlier expeditions and operate through its drill string. The winch has a cable length of 1200 m and all tools can be used in an open drill hole with a minimum diameter of 75 mm. Logging tools will be lowered into the coring riser or the DLS rods (diameter: 101.6 mm) as soon as the wireline coring, main hoist cables and the kelly are set aside. The power supply from the diesel engine on board of the GLAD800 will be utilised as a source for electricity.


Heave compensation is not available for the GLAD800. But experience has shown that swells of 1-2.5 m do not affect logging quality. Wave heights of more than 1 m very rarely occur at Laguna Potrok Aike. Even if they should occur during the drilling period, uncontrolled tool movements resulting in log depth shifts and incorrectly stacked records can be avoided by logging during the usually calm nights. The following methods for measuring physical parameters are available:

• Radiometric method: natural gamma rays; contents of K, Th and U; bulk density; neutron porosity; relative amounts of C, Ca, H, Fe, O, Si;

• Acoustic method: sonic velocity; ultrasonic view of the borehole wall with the borehole televiewer (BHTV); vertical seismic profile (VSP);

• Electric method: resistivity (DLL); self potential; dip and direction of layers (dipmeter); IP-effect;

• Magnetic method: magnetic susceptibility, magnetic field; • Other methods: borehole diameter (4-arm-caliper), salinity and temperature of the mud.

The vertical sampling rate of downhole logging is 5 cm on average. However, some methods like the dipmeter have a higher sampling rate (2 mm). In a cased borehole only a small number of the listed parameters can be measured because of the physical conditions. The proposed logging program for PASADO will provide all involved scientists with a unique data set for geological interpretation. Furthermore, geostatistical methods will be used to detect cycles in logging data. With some restrictions even changes in sedimentation rate can be determined (Molinie & Ogg, 1990; Wonik, 2001).

At every site logging operations will start immediately after the drilling has been terminated. Logging schedules are listed in Tab. 3 based on a mean standard logging time estimated at 50 m/h for five different slimhole sondes and calculated for the respective water and total drilling depths. Additionally, 4 hours are added to set up the logging equipment on the drill rig plus safety time for tool repairs or other unforeseeable events (10 hours).

Tab. 3: Proposed logging schedule for the anticipated three drilling sites at Laguna Potrok Aike. Drill site

Water depth (m)

Sediment depth (m)

Logging time (min.)

Installation and safety time

min-max (min.)

Total time for logging min-max

(min.) PTA 08-1A 35 50 102 240-840 342-942 PTA 08-1B 35 50 102 240-840 342-942 PTA 08-1C 35 50 102 240-840 342-942 PTA 08-2A 100 400 600 240-840 840-1440 PTA 08-2B 100 400 600 240-840 840-1440 PTA 08-2C 100 600 840 240-840 1080-1680 PTA 08-3 90 400 600 240-840 840-1440 Sum 1950 2946 1680-5880 4626-8826

Preliminary on-site processing will be carried out in the field to provide first lithologic

and stratigraphic interpretations. Additionally, correlation with seismic reflectors and MSCL data gives information about lithologic boundaries, occurrence of tephra layers and makes available a preliminary characterisation of the sediment record.

6.4 Initial field-based investigations For PASADO we will need a shore-based laboratory which will be set up in a shed on the premises of the INTA Potrok Aike field station. The shore-based laboratory will be equipped with the GEOTEK MSCL available through the ICDP operational support group. In addition to the MSCL, pore-water geochemistry and basic sedimentological investigations like preparation and microscopic investigation of smear slides will be carried out.

Logging of physical properties of sediment cores is part of the established standard methods of scientific deep drilling projects, e.g. IODP, ICDP, CRP and ANDRILL (e.g. Hodell et al., 2006; Huvenne et al., 2006; Niessen & Jarrard, 1998; Niessen et al., 1998). During drilling, the destruction-free parameters like density, p-wave velocity and magnetic


susceptibility are important in order to correlate cores and core segments (e.g. Pälike et al., 2005). Analysis of physical properties is done with the calibrated and computer-controlled MSCL (Weber et al., 1997; Best & Gunn, 1999; Zolitschka et al., 2001). Resolution depends on sensor type and varies between 0.5 mm and 10 cm. Physical properties will be measured in the field immediately after core recovery for all drill sites using the MSCL. Some proxies will be processed on-site to assist in drill-strategic and drill-technical decisions. Almost real-time on-site core logging is needed to combine the individual 3 m long core sections to form one composite profile by aligning the signals of core-logging data from triplicate drill sites. This is important to compensate for the small-scale loss of sediment at core breaks even with a core recovery rate of 100%. The relevance of core logging increases if core recovery is <100%. This procedure guarantees a recovery of continuous core sections which are essential for high-resolution paleoclimate investigations. Moreover, this approach produces an equivalent logging depth which has the advantage to correct for stretching and squeezing within core sections and between drill holes and thus provides the most accurate depth scale. Logging parameters will also provide first ideas about lithologies and thus can be used to infer e.g. paleoclimatic changes. Three main topics for analysis and interpretation of physical properties have been established:

• Physical properties of long cores are well suitable for statistically robust analyses to recognize o Different lithological units (e.g. by cluster analysis: Bücker et al., 2001) and o Milankovitch and sub-Milankovitch cycles (Hinnov, 2000);

• Parameters such as p-wave velocity and density are needed to combine sediment cores with seismic sections. This allows to project the one-dimensional (temporal) information derived from core analyses into temporal-spatial variations visible in seismic profiles;

• Certain physical parameters can also be used as a simple and fast proxy of climate induced changes in the investigation area instead of using cost-intensive and time-consuming laboratory analyses. The use of p-wave velocity and density as a proxy for grain size variations that was established at IODP cores may help to reveal Milankovitch-driven glacial-interglacial cycles. Grain size distributions are more precisely determined when investigating the spectral information and sonic attenuation of p-wave transmission seismograms in addition to the simple p-wave travel time (Breitzke 2000; Breitzke et al., 1996).

After drilling, all field measurements will be processed at respective home laboratories. Grain size distribution and other chemical and physical proxies will be measured on selected samples with conventional methods. Calibrated physical properties will then be much better understood and can be interpreted in terms of exceptionally high resolution variations in the sedimentary environment.

Geochemical investigations will also be carried out on-site. For these analyses a part of the core catcher sample will be used to squeeze out the pore water and to measure pH, electric conductivity, salinity and alkalinity. This information will provide yet another set of immediate data to support preliminary field-based interpretations. The pore water will be retained and later on analysed in the laboratory for its stable isotope composition.

On-site sedimentological analyses will be confined to determination of the weight of the core sections and the core catcher sample to estimate average densities of recovered sediments and to the production of smear slides. In the field laboratory the smear slides will be analysed microscopically and add substantial information to the MSCL data. Microscopical data may include qualitative estimates about grain size distribution, occurrence of volcanic tephra layers or presence of autochthonous calcites as well as indicate remnants of biological productivity like pollen, diatoms, chironomids, ostracods, aquatic snails or litoral plant remains.

6.5 Core storage, archiving and further lab-based processing The objective of PASADO is to recover high quality cores from Laguna Potrok Aike and to ensure that they will be archived in the best possible manner to be available for a wide range


of future investigations. Therefore, once handed over by the drillers to the scientific team onboard of the GLAD800, the cores will be handled very cautiously until finally stored in the GEOPOLAR cold room at the University of Bremen.

After saving the sediment of the core catcher (approximately 3 cm) and pushing the core liner out of the core barrel, a clear cap is placed on the “down” end of the core liner with acetone sealant and duct-tape and a blue cap is affixed to the “top” end of the liner. The core liner is then split into a 1.5 m “top” section and a smaller “bottom” section. The identifier for each core section is written on both, top and bottom halves with waterproof black markers and on opposite sides of the liner. “Up” arrows are also added on the pre-marked lines on the liner. Additionally, the upper (blue) cap is labelled. The label convention is:

• Expedition-Lake/Year-Site/Hole-Core/Device-Section • e.g.: GLAD8-PTA08-1A-1H-1 • Global Lake Drilling Expedition 8 – Laguna Potrok Aike, 2008 – Site 1, Hole A – Core 1,

drilled with HPC – Section 1 Abbreviations: e.g. hydraulic piston corer (HPC), core catcher (CC), extended nose (EXN)

After capping and labelling, core sections will be shelved in the on-board refrigeration unit and ferried to the shore-based laboratory at the end of every shift. Sediment cores will then be logged with the MSCL. Logging scientists process the data and correlate the holes using the SPLICER program to produce a composite depth scale. Thus depth offsets between holes will be determined and communicated to the GLAD800 to guide the drilling of subsequent holes.

All obtained data and drilling reports will be transferred in daily packages to the Drilling Information System (DIS) at GFZ Potsdam via a satellite-based internet connection. Internet access in the field will be provided by INTA.

After completion of shore-based analyses, core sections will be stored in boxes in the refrigerated container (reefer) which will be transported to Buenos Aires and shipped to Bremen after the drilling expedition has finished. Upon customs clearance cores will be stored in dark at +4°C in the GEOPOLAR cold room. First step will be lengthwise splitting of the cores. One of the split core halves will then be carefully cleaned and photographed digitally. This archive half will next be used for logging with the GEOTEK MSCL for P-wave velocity, electrical resistivity, and gamma ray attenuation. Following this procedure, the split archive half will be imaged and logged with a point sensor for magnetic susceptibility and with the XRF core scanner at 1 cm resolution. Furthermore, digital image and radiographic scans will be performed with the split core. Finally, archive halves will be stored in D-tubes and archived in the GEOPOLAR cold room.

Macroscopic core descriptions will be conducted on the work half. In addition, smear slides will be analysed microscopically to support sediment characterisation. Next, volumetric samples for water content and dry bulk density will be taken from the composite sedimentary sequences of each drill site. In parallel and from the same depths subsampling for geochemistry, stable isotopes and biological proxies (pollen, diatoms, chironomids, other algae) will be carried out. After drying and weighing the same sample will be used to analyse total organic and inorganic carbon, nitrogen and sulphur. Depending upon need, a U-channel will be taken continuously for rock- and paleomagnetic investigations and for further high-resolution XRF scanning. This U-channel will constitute an additional archive.

With the exception of some critical components (which have not yet been determined) that might deteriorate immediately after the contact with oxygen due to core splitting and therefore need to be sampled soon after core opening, all other sampling activities will be deferred and will occur after the financial aspects of their analyses have been assured. High-resolution sampling is anticipated for one composite profile for every drill site. The amount of material needed per sample depends on the demands of the various analyses and on the concentration of e.g. certain microfossils. The science party of PASADO will follow sampling policies and regulations as set up by IODP and adapted by ICDP.


7. Expected scientific and societal benefits of the proposed work The major scientific objective is to obtain a long sedimentary record that will provide the first continuous, quantitative and high-resolution paleoclimate and paleoenvironmental record from the non-tropical southern mid-latitudes throughout the last glacial-interglacial cycles. Moreover, we will produce quantitative climate reconstructions based on multiple proxies (pollen, chironomids, stable isotopes, organic geochemistry) that will be compared with the output of climate models. Through this proxy-modelling alliance it will be possible to derive a much more precise understanding of the underlying climate forcing. As an additional achievement the phasing of wet-dry cycles and other high-frequency climate shifts will be determined for southern South America. These will then be linked to climatic oscillations of South America (El Niño) and Antarctica (AAO).

Climate models will be tested with reconstructions of the past that are different from present day conditions to support and improve climate model estimations of future climate changes. Thus possible causes and regional patterns of climate anomalies in southern South America will be analysed by means of climate simulations with a high-resolution regional climate model for different periods of the past and for the preindustrial period. Regional simulations will address the role of precipitation and evaporation on lake levels, on moisture sources and the influence of external climate forcing, such as orbital parameters, solar variability and past and future impacts of atmospheric greenhouse gas concentrations. Also relationships between large-scale atmospheric circulation and local climate anomalies for past and future climates will be considered.

Laguna Potrok Aike is of global geological importance with regard to being the first large (maar) crater lake studied for its entire sedimentary record. It thus will be possible to develop and calibrate lithofacies models for lacustrine systems covering several glacial to interglacial cycles, i.e. from the time of its phreatomagmatic formation. Based on typical lacustrine sedimentation rates of ~1 mm a-1 the overall temporal resolution will be much higher compared to other long lake sediment records like Lake Baikal or Lake El’gygytgyn. This site will become the first maar where a scientific drilling project will attempt to penetrate lacustrine sediments and to reach the underlying volcaniclastic rocks. This approach will produce new insights into the early geological history of maar craters and processes that led to the formation of the modern lake.

After all, investigations within the framework of PASADO will also have societal benefits. The major economic income in the Province of Santa Cruz is related to extensive sheep farming. Like during colonisation in the late 19th century this is a rather drought-sensitive economy until today. However, since that time climate started to become drier resulting in decreased precipitation and increased evaporation. As this climatic process is still ongoing and was even accelerating during the last decade, climate models will be used to extrapolate the impact of this change on the economy of the 21st century.

8. Project management Most PIs are from countries that are already members of the ICDP except for Argentina, Sweden and Switzerland. Sweden intends to become a member in 2009 (cf. letter of support in A8), whereas we are still working to convince Argentina to take this step forward (cf. A8). The situation with Switzerland has been and still is tackled actively by the Swiss PIs (cf. A8). However, a consensus about a Swiss ICDP membership has not yet been reached.

All PIs have considerable experience with the design and planning of scientific drilling operations on lakes and with international cooperation. B. Zolitschka and C. Ohlendorf will be the overall science coordinators of PASADO and act as co-chief scientists in the field. Both have a long standing record with international lake coring projects. Lake drilling will be contracted to DOSECC. We have a good working relationship with its director D. Nielson who developed the GLAD800 drill rig and has a wealth of experience with previous lake drilling projects.


The fieldwork at a remote site like Laguna Potrok Aike – the next settlement is Río Gallegos in a distance of 112 km – needs a very thorough planning. For scientific drilling operations it is crucial to set up docking facilities and a field camp for housing and living as well as a field laboratory. The field camp will be organised on the property of the INTA field station. About ten trailors will be hired from local companies in Río Gallegos for sleeping, eating and living. Food and water like all the other necessary items will be provided with a daily shuttle from Río Gallegos. All the logistics, like arrangements for housing, meals, supply trips, airport shuttle services and communication with locals will be overseen by a local Argentinean whom we would like to hire as an on-site logistics coordinator. He or she will be fluent in English as well as in Spanish and also interacts with the technical support group.

For technical support we have ascertained the help of Capt. Moreteau, a nautical pilot with a license for ocean going ships along the South Atlantic shores and through the Strait of Magellan. For several years Capt. Moreteau served as a geological consultant for many lake-based scientific operations in Patagonia but also for commercial projects, e.g. harbour construction at Lago Argentino or building a pipeline to connect offshore oil fields. He will be the ideal person to take care for road construction to the lake and for construction of the dock. In addition, he will provide the RV “Lago Cardiel”, a catamaran equipped with powerful engines to (1) manoeuvre the coring platform and (2) serve as a shuttle boat between shore and drill rig. Capt. Moreteau with his crew will run the catamaran as well as install and run communication via vhf and hf radios between the platform, the shore and the field camp. Moreover, all other technical support, like fuel, oil, lubricants, forklift, backhoe, installation of land anchor points but also trash disposal will be overseen by him.

H. Corbella, N. Maidana and B. Zolitschka will be contact persons with local political organisations (government of the Province of Santa Cruz or the City of Río Gallegos) and the national government, if necessary. They also keep close links with the owners of nearby estancias and with regional and national radio and TV stations as well as with newspapers.

Fig. 14: On-site management structure for one shift of PASADO.

All information related to regional geology and volcanology will be provided by H. Corbella and B. Ercolano. The seismic site survey is the responsibility of F. Anselmetti who works in close collaboration with D. Ariztegui, M. DeBatist, F. Niessen and C. Gebhardt. C. Ohlendorf will oversee all aspects of core handling and curation. F. Niessen will be in charge of the GEOTEK MSCL in close collaboration with D. Ariztegui. T. Wonik takes care of


downhole logging operations. With F. Anselmetti and D. Ariztegui we have two of the PIs of the very successful Peten-Itza Drilling Project in our team. This will guarantee that previous experiences will be transferred to PASADO.

For subsequent and detailed analyses of sediment cores at their respective home laboratories coordination responsibilities are as follows: volcaniclastic rocks (H. De Wall), tephrochronology (S. Wastegard), lacustrine sedimentology (C. Ohlendorf, B. Zolitschka), stable isotopes (A. Lücke), pollen (F. Schäbitz), diatoms (N. Maidana), paleomagnetics (L. Brown), microfacies analyses (P. Francus), paleoclimatic reconstruction (R. Bradley) and deep biosphere (D. Ariztegui).

The on-site management structure (Fig. 14) follows the successful approach of the Peten-Itza project. Drilling operations will be carried out in 2 shifts of 12 hours each. On board of the GLAD800 each shift consists of one drilling supervisor and three drillers from DOSECC and one co-chief scientist and three scientists of the scientific party. The co-chief scientist will interact closely with the DOSECC drilling supervisor for on-site decision making. The three scientists are responsible for core curation, handling of the core catcher sample and to assist as a driller’s helper. For the field laboratory the two shifts consist of three scientists: the core logging scientist will operate the MSCL and construct composite sediment profiles applying the software package SPLICER. The sedimentologist will take care for organising the cores in the reefer, packing them for shipping and taking samples from the core catcher for smear slide preparation. The geochemist will squeeze interstitial water from the core catcher samples which has to be done and measured in the field. Altogether, eight people from DOSECC and 14 scientists (8 platform-based and 6 laboratory-based) will be necessary for a smooth operation.

9. International science team Since 2002, the start of the DEKLIM project SALSA, we have established a strong German-Argentinean collaboration which since then included more and more European scientists. With the call for the ICDP Workshop PASADO, held March 15-19, 2006 in Río Gallegos (Argentina), the list of interested scientists and included disciplines extended tremendously. Following this call 52 participants from 5 continents and 11 countries (Tabs. 4, 5) were willing to cooperate and were invited to Patagonia. More scientists expressed their interest but were unable to attend. All of these and some additional scientists who expressed their interest of participation in PASADO after the workshop reports appeared in “Scientific Drilling” (Zolitschka et al., 2006a) and “PAGES News” (Zolitschka et al., 2006c) are listed in Tab. 5.

Altogether, there are currently 58 scientists (36% of them are female) representing a wide geographical coverage and a balanced expertise: 29 different disciplines shape PASADO to a vivid inter- and multidisciplinary geoscience approach. This is reflected in the different topics that were discussed during the PASADO workshop (Zolitschka, 2006; Zolitschka et al., 2006a, c). All scientists mentioned in Tab. 5 constitute the international science team of PASADO. This team includes drilling experts as well as scientists with most of them following clear multidisciplinary and interdisciplinary objectives.

Tab. 4: Countries covered and number of working groups involved per country. Country Number of working groups Number of scientists Argentina 11 17 Germany 10 14

USA 6 8 Canada 6 7

U.K. 3 5 Switzerland 2 2

Australia 1 1 Belgium 1 1

Chile 1 1 Poland 1 1 Sweden 1 1

total 43 58


Tab. 5: Alphabetical list of scientists who constitute the international science team of PASADO with their respective affiliations, countries and scientific disciplines.

First name Last name Affiliation Country Speciality Flavio Anselmetti ETH-Zurich Switzerland seismic stratigraphy Daniel Ariztegui University of Geneva Switzerland limnogeology Ramiro Barberena DIPA-IMHICIHU, Buenos Aires Argentina archaeology Luis Borrero DIPA-IMHICIHU, Buenos Aires Argentina archaeology Raymond Bradley University of Massachusetts USA paleoclimatology Laurie Brown University of Massachusetts USA paleomagnetism Hugo Corbella UNPA & MACN, Buenos Aires Argentina volcanology Andrea Coronato CADIC-CONICET, Ushuaia Argentina Quaternary stratigraphy Marc DeBatist Ghent University Belgium seismic Helga DeWall University of Wuerzburg Germany volcanology Bettina Ercolano UNPA, Río Gallegos Argentina Quaternary stratigraphy Pierre Francus INRS, Quebec Canada Microsedimentology Diego Gaiero Universidad de Cordoba Argentina aeolian dust Catalina Gebhardt AWI Bremerhaven Germany Seismic stratigraphy Claudia Gogorza CONICET IFAS, Tandil Argentina Paleomagnetism Torsten Haberzettl University of Goettingen Germany Sedimentology Miguel Haller UNPSJB, Puerto Madryn Argentina Volcanology Sonja Hausmann University of Arkansas USA Diatoms Julie Jones University of Sheffield U.K. climate modeling Kyeong Kim University of Arizona USA 14C, 10Be Hedy Kling University Crescent Canada non-siliceous algae Scott Lamoureux Queen's University Canada Paleohydrology Andreas Lang University of Liverpool U.K. OSL dating Isabelle Larocque INRS, Quebec Canada Chironomids Peter Leavitt University of Regina Canada biochemistry Andreas Luecke Research Centre Juelich Germany stable isotopes Nora Maidana University of Buenos Aires Argentina Diatoms Fabiana Martin CEQUA, Punta Arenas Chile archaeology Ulrike Martin University of Wuerzburg Germany volcanology Julieta Massaferro ILPLA, Instituto de Limnologia Argentina chironomids Christoph Mayr University of Munich (LMU) Germany stable isotopes Elizabeth Mazzoni UNPA, Río Gallegos Argentina remote sensing, GIS Beata Messyasz University of Poznan Poland phytoplankton J. Daniel Moreteau Puerto Madryn Argentina geological consultants Alexandra Nederbragt University College, London U.K. geochemistry Dennis Nielson DOSECC USA engineer Frank Niessen AWI, Bremerhaven Germany physical properties Christian Ohlendorf University of Bremen Germany sedimentology Gabriel Oliva INTA, Río Gallegos Argentina logistical support Marta Paez Universidad de Mar del Plata Argentina palynology Carlos Paterlini Serv. de Hidrografia Naval Argentina magnetometry Reinhard Pienitz Université Laval, Quebec Canada diatoms Eduardo Piovano Universidad de Cordoba Argentina sedimentology Jorge Rabassa CADIC-CONICET, Ushuaia Argentina Quaternary stratigraphy Frank Schaebitz University of Cologne Germany palynology Guillaume St-Onge Université du Québec à Rimouski Canada paleomagnetics Juergen Thurow University College, London U.K. image analysis Horacio Toniolo University of Alaska, Fairbanks USA sediment modeling Paul Vallelonga Curtin University of Technology Australia Pb and Sr isotopes Christel van den Bogaard IFM-GEOMAR, Kiel Germany tephrochronology Sebastian Wagner GKSS Research Centre Germany climate modeling Stefan Wastegard University of Stockholm Sweden tephrochronology Cathy Whitlock Montana State University USA charcoal Martin Widman University of Birmingham U.K. climate modeling Michael Wille University of Cologne Germany palynology Thomas Wonik GGA, Hannover Germany downhole logging Zhaohui Zhang University of Massachusetts USA organic geochemistry Bernd Zolitschka University of Bremen Germany sedimentology


10. Time table A realistic time schedule for the PASADO drilling project is necessary and required for all pre-drilling activities like funding, planning, permitting and shipping but of course also for the actual field work in Argentina. Delays in this timeline have to be avoided as much as possible as they usually waste financial resources and unnecessarily question the project management. However, unpredictable changes in the time schedule often occur and are related to factors that are difficult to foresee like delayed notification of funding agencies, especially if five national funding agencies from different countries have to be considered in addition to ICDP, like in the case of PASADO. Moreover, sudden changes of governmental or custom regulations or delays in shipping have to be taken into consideration. To minimize such effects good communication between PIs, funding agencies, DOSECC and all scientific participants is the key aspect for success. Tab. 6: Work schedule with milestones for the process of funding (black), a fast track option for drilling in 2008 (blue) and a slow track option for drilling in 2009 (red).

Years 2007 2008 2009 Months 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 9 101112 1 2 3 4 5 6 7 8 9 101112

PASADO proposal submitted Informal ICDP decision Supportive proposals submitted* Formal ICDP decision Supportive proposals decided Pre-mobilisation site visits Equipment leaves to Argentina Mobilization Drilling Demobilization Equipment returns Core splitting and scanning Sampling parties

*to DFG, NSF, NSERC, SNF and VR

We plan the drilling operations to be carried out in the months of January to March 2008 (Tab. 6). This time of the year is selected as the most appropriate with longest daylight conditions and highest daily temperatures (10-13°C) during southern summer. This “fast track” option (Tab. 6) will be possible if funding notifications are received in less than half a year after the informal ICDP decision was made. If this should not be the case, the “slow track” option (Tab. 6) provides ample time for all the funding to be secured, as this implies that drilling will be carried out one year later from January to March 2009. In any case, pre-planning activities will start immediately after notification by ICDP.

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