A HIGH RESOLUTION MULTI-PROXY SEDIMENT STUDY IN SOUTHERN PATAGONIA, ARGENTINA: THE SALSA PROJECT

Southern hemisphere paleoclimatic reconstructions from terrestrial archives are rare. There is a need for such data, since climate models show that the southern hemisphere might play a key role in the global climate system. The interdisciplinary project SALSA aims to extract paleoclimatic information from crater lakes in the Pali Aike Volcanic Field (PAVF, 50° - 52° S). Between 3,78 - 0,01 Ma several maars were formed, some of which are permanent lakes. The last glaciation did not reach the area. Therefore, the PAVF has an excellent potential to obtain long sediment records. During the first field trip (2002) many temporary lakes of the PAVF were surveyed and Lag. Potrok Aike (diam.: 4 km, 100 m deep) and Lag. Azul (diam.: 700 m, 52 m deep) were studied. Five out of 16 short sediment cores from latter lakes were analyzed for sedimentology, microfossils and stable isotops. Sixteen radiocarbon dates provide a time control spanning the last 2000 years. For the first time it was possible to obtain a late Holocene palaeoenvironmental reconstruction for southernmost Patagonia based on this high resolution multi-proxy study. Lag. Azul lies 60 m below the crater rim and is protected from strong winds due to steep crater walls. The water body is stratified and has sub-oxic conditions at the sediment/water interface. Sediments are made of biogenic ooze. Lag. Potrok Aike is a maar lake probably originated from a phreatomagmatic explosion. It is fully exposed to strong westerly winds and therefore not stratified. Sediments are laminated clastic silts. The C/N ratio in Lag. Potrok Aike indicates that sediment organic matter is mainly of planktonic origin. Pollen spectra reflect the actual situation of Patagonian steppe vegetation since c. 2000 yr BP. Abundant charcoal particles in the sediments of both lakes indicate a major fire event around 335/350 yr BP. Different proxies show changes in the upper part of the records probably related to the start of human impact with sheep and cattle raising settlers since the end of the last century. In February 2003 field work is concentrated to recover long sediment records from both lakes. Those will be analyzed in order to obtain high-resolution information about the Holocene/Pleistocene paleoclimate. A regional paleoclimate model will be developed which can provide input for modelling on broader scale.