High-resolution qualitative environmental and climatic reconstruction for the last glacial interglacial cycles - the sediment record of the ICDP site Laguna Potrok Aike, Argentina (PASADO-Core)
Zusammenfassung der Projektergebnisse
The main goal of this project was to study the last glacial cycle of the Southern Hemispheric midlatitudes (52°S) using a unique lacustrine sediment record from Laguna Potrok Aike. First results were compared with marine and ice core data and in future also will be tested against modeling results in order to help understanding how climate interacts globally. With funds provided by PASADO-core for drilling of the sediment record of Laguna Potrok Aike, a 770 ka old maar lake in the dry steppe of southern Patagonia (Argentina), a unique record of environmental and climate variation was recovered and investigated. During the PASADO expedition the application of field based physical property measurements using a GEOTEK Multi Sensor Core Logger made it possible to correlate core segments of a triplicate (5022- 2) and a quadruplicate (5022-1) drill site already during the drilling process, which was important for drill-strategic and drill-technical decisions. Core documentation, high-resolution core logging and archiving for internationally funded science projects was one major focus of PASADO-Core as well as the preparation of a stacked composite profile ready for subsampling by international collaborating science teams. Within the project, a new protocol for sediment core treatment was developed, documented and applied to the 106 m long PASADO site 2 composite profile (5022-2CP) that consists of 99 core sections and was sampled in consecutive 2 cm steps. A total of 5089 samples with 35,623 subsamples were taken which were and still are analysed by the different international research groups involved in the project. The sediment description revealed a surprisingly high percentage (>50%) of mass movement deposits (MMDs) that increase downward in frequency. MMDs thus are an important part of the sedimentation history of the lake basin. The increased occurrence of MMDs during the glacial period presumably is related to rapid and frequent lake level changes that might have enforced the collapse of slopes. The general decrease of MMD occurrence with time is probably the effect of decreasing sub-aquatic relief energy, slope consolidation and a less inclined slope angles as basin infill progresses. For the composite profile, subtraction of all MMDs allowed displaying data on an event-corrected composite depth scale. New techniques for high resolution sediment core sampling and analyses were applied in an international and interdisciplinary research team. An age model was developed that reveals the 14 14 advantages but also the limits of AMS C-dating. Namely the comparison of the AMS C-chronology with variations of the geomagnetic relative paleointensity reveals temporal offsets with respect to 14 dated excursions of the geomagnetic field that are associated to the uncertainties of AMS C-dates older than 40 cal. ka BP, which can be ascribed to the limits of the radiocarbon method. First preliminary OSL-dating results point in the same direction and will result in a future modification of the existing chronology. First geochemical data and physical properties in combination with age determinations, allow qualitative climate and environmental reconstructions at multi-millennial to decadal resolution. Altogether, these results provide information about lacustrine productivity, origin of organic matter, allochthonous sediment transfer, hydrological variations and sedimentological processes, all of which are related to climatic forcing mediated through the environment. In particular, parameters such as BSi, TOC and TIC content were used to reconstruct lake-level variations. Carbonate-free sediments indicate that high lake-level conditions have prevailed during the last glacial which are probably linked to increased runoff due to permafrost prevalence and reduced evaporation due to colder temperatures. A reduced influence of Southern Hemispheric Westerlies (SHW) may have caused these high lake levels. During the Glacial, maxima of organic matter content and diatom blooms occurred synchronously with southern hemispheric glacial warming events such as the Antarctic A-events, the postglacial warming following the LGM and the Younger Dryas chronozone. With the beginning of the Holocene, a completely different lacustrine system was established because permafrost disappeared and the positioning of the SHW over southern Patagonia gave rise to strong and dry winds. Under these conditions, high sediment TIC concentrations mirror increased endogenic precipitation of carbonates linked to low lake levels. The onset of inorganic carbon precipitation around 9.4 cal. ka BP has been associated with the southward shift of the SHW over the latitudes of Laguna Potrok Aike. A first compilation of interdisciplinary scientific results generated in the framework of PASADO was realised in a special issue of the peer-reviewed Journal “Quaternary Science Reviews”. The synthesis of data from Laguna Potrok Aike exposes the role of the SHW in the global climate system as one of the most challenging scientific debates about climate variability today. It is currently investigated how changes in SHW position and/or intensity influence the global ocean circulation and the related oceanto-atmosphere heat and gas fluxes. A better understanding of this feed-back system would allow a much better estimation of consequences for the currently ongoing human-induced atmospheric greenhouse gas increases.
Projektbezogene Publikationen (Auswahl)
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(2009). Environmental history of southern Patagonia unravelled by the seismic stratigraphy of Laguna Potrok Aike. Sedimentology, 56, 873–892
Anselmetti, F., Ariztegui, D., De Batist, M., Gebhardt, C., Haberzettl, T., Niessen, F., Ohlendorf, C. and Zolitschka, B.
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(2009). The Laguna Potrok Aike Scientific Drilling Project PASADO (ICDP Expedition 5022). Scientific Drilling 8, 29-34
Zolitschka, B., Anselmetti, F., Ariztegui, D., Corbella, H., Francus, P., Ohlendorf, C., Schäbitz, F.
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(2011). Comparative study of infrared techniques for fast biogeochemical sediment analyses. Geochemistry Geophysics Geosystems 12, Q10003
Hahn, A., P. Rosen, P. Kliem, C. Ohlendorf, and B. Zolitschka
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(2011). Deciphering lake and maar geometries: Seismic refraction and reflection survey in Laguna Potrok Aike (southern Patagonia, Argentina). Journal of Volcanology and Geothermal Research 201, 357-363
Gebhardt, AC, De Batist M, Niessen F, Anselmetti FS, Ariztegui D, T. H, Kopsch C, Ohlendorf C and Zolitschka B
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(2011). New insights into paleoenvironmental changes in Laguna Potrok Aike, southern Patagonia, since the Late Pleistocene: The PASADO multiproxy record. The Holocene
Recasens, C, D. Ariztegui, C. Gebhardt, C. Gogorza, T. Haberzettl, A. Hahn, P. Kliem, A. Lisé-Pronovost, A. Lücke, N. Maidana, C. Mayr, C. Ohlendorf, F. Schäbitz, G. St-Onge, M. Wille, B. Zolitschka
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(2011). The PASADO core processing strategy – A proposed new protocol for sediment core treatment in multidisciplinary lake drilling projects. Sedimentary Geology 239, 104-115
Ohlendorf C., Gebhardt, A.C., Hahn, A, Kliem, P., Zolitschka, B.
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(2012). High-resolution paleomagnetic records from Laguna Potrok Aike (Patagonia, Argentina) for the last 16,000 years. Geochemistry Geophysics Geosystems 16
Gogorza, C.S.G., Irurzun, M.A., Sinito, A.M., Lisé-Pronovost, A., St-Onge, G., Haberzettl, T., Ohlendorf, C., Kastner, S. and Zolitschka, B.
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(2012). Seismic evidence of up to 200 m lake-level change in Southern Patagonia since Marine Isotope Stage 4. Sedimentology 59, 1087-1100
Gebhardt, A.C., C. Ohlendorf, F. Niessen, M. De Batist, F.S. Anselmetti, D. Ariztegui, P. Kliem, S. Wastegård, B. Zolitschka
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(2012). The last Glacial-Interglacial transition in Patagonia, Argentina: the stable isotope record of bulk sedimentary organic matter from Laguna Potrok Aike. Quaternary Science Reviews
Zhu, J., Lücke, A., Wissel, H., Müller, D., Mayr, C., Ohlendorf, C., Zolitschka, B.
