Diatoms as indicators of hydrologic and climatic change in Lake Potrok Aike – A step toward deciphering changing patterns of paleoecological conditions in South

RECASENS, C.; MAIDANA, N. I.; ARIZTEGUI, D.; ANSELMETTI, F.; PASADO SCIENCE TEAM

Viena (Austria)

Workshop; 2nd International ICDP Workshop PASADO; 2010

ICDP

Diatom analysis of the sediment record from Laguna Potrok Aike, obtained in the framework of the ICDP-sponsored project PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Program), provides new climatic information since the Late Pleistocene. Previous multi-proxy studies in the area have characterized the environmental history of the drylands in the Patagonian Steppe for the last 16,000 cal BP. A low resolution diatomological study has been performed on PTA-1D, a 97.3 m long sedimentary core recovered from the central part of the lake covering at least the last 50,000 years. A set of 94 samples was processed for taxonomical and quantitative analyses. We use variations in diatom concentration and in their floristic assemblages, to track changes in lake conditions and tackle the most interesting sections to carry out higher resolution analyses. Diatom concentrations fluctuate between 0 and 7x108 valves/gr along the core and so far more than 200 different taxa have been identified. A CONISS cluster analysis (based on the sum of squares method) was performed and eight preliminary zones were distinguished based on the different diatom assemblages. Cyclotella agassizensis dominates in the top part of the core along with Thalassiosira patagonica, although these indicators of more brackish conditions become rare or disappear in older sediments. Variations in the planktonic/non-planktonic species ratio show a particularly high amount of non-planktonic taxa between 12 and 17m sediment depth. The latter could indicate a relative lower lake-levels and/or periods of ice-cover development. Nevertheless, a combination of these results with other proxies is necessary to further develop these hypotheses. The multi-proxy approach of the PASADO project combined with the modern training set for Patagonia (ongoing PIPA Argentine project) will provide unique paleoecological information for this remote area of the Southern Hemisphere.