Multiproxy Reconstruction of Hydrological Changes during the Late Holocene in Laguna Chaltel (Southern Patagonia, Argentina)

RAMÓN MERCAU, J; MAIDANA, N. I.; LAPRIDA, C.; ORPELLA, G.; MASSAFERRO, J. ; QUINTANA, F. A.; SALSA SCIENCE TEAM

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Congreso; II International Symposim "Reconstructing Climate Variations in South America and the Antarctic Peninsula over the last 2000 years"; 2010

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Laguna Cháltel (49° 57’ S- 71° 06’ W) is a crater lake located in the semiarid steppe of Patagonia. Several cores obtained by the South Argentinean Lake Se- diment Archives and Modelling international research project were analyzed using a multi-proxy approach to reconstruct the paleoenvironmental history of the lake. Changes in diatom, chironomid and ostracod assemblages and de- tailed geochemical analysis provided information about past lake water level fluctuations and hydrological changes in the watershed. Between 4500 and 3900 cal. BP, relatively moist conditions can be inferred from ostracods. From 3900 to 3150 cal. BP, there is geochemical evidence of allochthonous input and a shift to saline conditions implied by marked changes in ostracods. Both indicate low water level by that time. Between 3150 and 2400 cal. BP, condi- tions became moister with a concurrent lake level rise. Moderate salinities and the presence of abundant marginal vegetation are inferred from ostra- cods and diatoms. At 2400 cal. BP changes in diatom and ostracod assem- blages suggests that the lake level rose markedly. These conditions may have triggered lower salinities, and higher productivity. A noticeable increase in diatoms may have been enhanced by expansion of littoral habitats. The high lake level may point to a less arid climate or less evaporation due to higher re- lative humidity, less wind or seasonal ice cover. A new shift to cooler/moister conditions took place at around 1400 cal. BP, when modern lake conditions were established. The presence of littoral and semiterrestrial chironomid species confirms diatom interpretation of expansion of littoral habitats. The present work, which was partially  financed by the Southern Patagonia Inter- disciplinary Project (PIPA) (PICTR 2006 – 2338) and includes neolimnolo- gical information obtained by its members, enhances the understanding of spatial patterns of past hydrological changes in Southern Patagonia steppe, indicating further hydrological variations during the late Holocene.