LATE HOLOCENE ENVIRONMENTAL HISTORY OF SOUTHERNMOST PATAGONIA, ARGENTINA; POLLEN ANALYSES OF FIVE SEDIMENT CORES FROM VOLCANIC LAKES

The interdisciplinary project SALSA aims to fill the gap of paleoclimate reconstructions for the southern hemisphere from continental archives. It provides information by high resolution multi-proxy analyses of sediment cores from crater lakes in the Pali Aike Volcanic Field (PAVF) located between 50° and 52° S in Patagonia, Argentina. The PAVF is a tectono-volcanic belt 50km wide and >150km long located 80km west of the city of Río Gallegos, immediately north of the Strait of Magellan, where several maars formed between 3,78 to 0,01Ma. The last (Llanquihue) glaciation, did not reach this area. Five short sediment cores (length: 90-130 cm) from Laguna Azul (two cores) and Laguna Portok Aike (three cores) were analyzed for several proxies including microfossils. Sixteen AMS-radiocarbon dates provide a time control covering the last 2000 years. Paleoenvironmental reconstruction shows that in pollen diagrams from both lakes pollen types of the Patagonian steppe vegetation dominate without major fluctuations. The dominant taxa are Poaceae and Asteraceae. The dwarf shrub Empetrum shows higher values in Laguna Azul than in Laguna Potrok Aike. Therefore pollen spectra represent mainly the actual vegetation pattern in southern Patagonia i.e. a more xeric steppe type typical for the eastern part and a slightly more humid steppe type occurring in the western part of the area. Higher contribution of Andean forest taxa (=long distance transport) in Laguna Azul is remarkable, because it is located ca. 60 km further east of the steppe-forest border than Laguna Potrok Aike. Major changes occur in the upper parts of the pollen diagrams (20-0 cm in Laguna Potrok Aike and 50-0 cm in Laguna Azul). An increase in Rumex pollen is interpreted as indicator for pasture and probably shows the start of human impact by sheep and cattle raising settlers since the end of the last century. The contemporaneous increase in Pediastrum algae points to a change in water ecology at both lakes probably related to an increase in nutrients.