High-resolution and continuous lacustrine records reaching back to the final stages of the Last Glacial are rare for South America. Most shallow and even intermediate deep lakes dried out either during the Full Glacial, the Late Glacial transition or the early Holocene. In SE Patagonia only the maar Laguna Potrok Aike (51°58`S, 70°23`W) is deep enough (100 m) to prevent total dessication. There are, however, clear geomorphological, seismic stratigraphic and sedimentological indications of lake level fluctuations ranging from +20 to 30 m (relative to present day lake level) that indicate marked hydrological changes and make this site an ideal ICDP deep drilling target. The formation of Potrok Aike maar is Ar/Ar-dated to 770 ka and thus the lake potentially holds a sedimentary infill covering several glacial cycles. Deep sparker and multi-channel airgun seismic surveys support the presence of >150 m of lacustrine sediments on top of >300 m of volcanic breccias. We thus intend to use the GLAD800 coring system to retrieve long sedimentary cores at three different drilling sites: (1) In the central deep basin to obtain a continuous sedimentary sequence in order to reconstruct environmental conditions for the last glacial cycles. These will be compared to other long terrestrial sites from South America, to Antarctic ice cores and to Circum-Antarctic marine records. Climate and dust modelling will be used to improve correlations. (2) On the lake shoulder (30 m water depth) to obtain a discontinuous sediment sequence in order to unravel the lake level history and to investigate the nature and age of possible unconformities. (3) Near the lake margin to drill through the deep volcanic breccia. This includes inclined coring from the lake through the maar-bedrock transition into the molasse basement. Laguna Potrok Aike will be the first Quaternary site providing not only a paleoenvironmental record but also unique data about the phreatomagmatic formation of maars allowing a better understanding of volcanological processes behind their development. During a pilot study the continuous sedimentary record from the deep basin was dated with decadal resolution since 16,000 cal. BP combining 21 AMS radiocarbon and 3 tephra ages. The carbonate content is used as an indicator of lake water volume variations while Ti reflects minerogenic influx via runoff. Both proxies provide a conclusive image of hydrological variability. Based on these hydrological proxies we determined moist conditions from the onset of the record until the early Holocene (8700 cal. BP) interrupted by one pronounced dry period (13,200-11,400 cal. BP). This dry period is contemporaneous to the Northern Atlantic Younger Dryas chronozone but unlike in the Northern Hemisphere, it is not only dry but also warm. Between 8700 and 7300 cal. BP the lake reached the lowest lake level of the entire record. After this 1400 year-long dry period the lake recovered and lake level rose. Since 7300 cal. BP minor hydrological fluctuations were recorded until AD 1480 when the water level increased to the late Holocene maximum, a time interval corresponding to the Northern Hemisphere Little Ice Age. Since AD 1940 the lake level receded until today due to the 20th century warming.
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