Patagonia

Patagonia

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Lacustrine ostracodes as indicators of Late Quaternary environmentalchange in Patagonia, Argentina

Modern ostracode assemblages from Lakes Cari-laufquen (41°S, 69°W) and Lago Cardiel (49°S, 70°W) catchments were used to characterize aquatic habitats (Schwalb et al., 2002; Schwalb 2003; Cusminsky et al., 2005), and to establish a transfer function for lake water conductivity (Viehberg et al., submitted). Multi-proxy evidence from an eleven meter long core from Lago Cardiel (49°S, 76 m water depth, 379 km2 area, ~ 10km east of the Andean cordillera) show that the lake at the end of the Last Glacial Maximum (LGM) was small, shallow and saline, according to ostracode assemblages represented by Limnocythere rionegroensis var. saline.

By 13 cal kyr BP the lake had nearly dried out indicating that despite overall rapidly increasing temperatures after 17 cal kyr BP precipitation did not increase south of latitude 40°S. After 13 cal kyr BP lake level rose rapidly, culminating in a +55 m shoreline at 10,7 cal kyr BP. Presence of planktic diatoms and the highest ostracode diversity represented by Limnocythere patagonica, Kapcypridopsis megapodus, Eucypris fontana and E. virgata indicate a large and deep lake which suggests that the SW were weak allowing easterly moisture to advance towards the Andes.

By 7,5 cal kyr BP lake level dropped to a level close to present. Benthic diatoms became abundant, and the modern ostracode assemblages, consisting of mainly E. fontana and L. patagonica in minor abundance, was established indicating reduction in precipitation to present-day levels. The occurrence of drift deposits after ~ 6,8 cal kyr BP reveals the presence of a wind-driven lake current, which indicates strong and persistent SW at a latitude of 49°S during the middle and late Holocene.