The diatom record of Laguna Potrok Aike, Argentina: inferring climatically-induced hydrological changes since the late Pleistocene

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

Minnesota, EE UU de Norteamérica

Simposio; 21st International Diatom Symposium; 2010

International Society for Diatom Research

Diatom analysis in a sediment core from Laguna Potrok Aike, a maar lake located in Southern Patagonia, provides a continuous record of hydrological and climatic changes since the Late Pleistocene.  This study is done within the framework of the Potrok Aike Maar Lake Sediment Archive Drilling Program (PASADO), a lake drilling operation in Southern Patagonia sponsored by the ICDP. Diatoms are widely used to characterize and often quantify the impact of past environmental changes in aquatic systems. A low resolution diatomological analysis was performed on PTA-1D, a 97.3 m long sedimentary core from the central part of the lake that spans approximatively the last 50 kyrs (ongoing radiocarbon datings will better constrain the age model).We use variations in diatom concentration and in their taxonomical assemblages, blended with other proxies, 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 in the sediment. A cluster analysis (based on the sum of squares) was performed in our record to determine the zones with different diatom assemblages. While Cyclotella agassizensis dominates in the top part of the core together with Thalassiosira patagonica, as previously seen in earlier studies on this lake, these indicators of more brackish conditions are rare or not found at all in deeper sediments. Variations in the planktonic/non-planktonic species ratio, with a particularly high amount of non-planktonic taxa between 12 and 17m depth, could point toward lower lake-level stands or periods of ice-cover in the lake. Nevertheless, a correlation with other proxies is necessary to further develop these hypotheses.  The multi-proxy approach of the PASADO project, and its combination with the modern training set for Patagonia that will be produced within the framework of the ongoing PIPA argentine project, will provide unique paleoecological information for the Southern Hemisphere.