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

RAMÓN MERCAU, J. 1, MAIDANA, N. 1, ORPELLA, G. 2, LAPRIDA, C. 1, MASSAFERRO, J. 2, FEY, M

Valdivia

Congreso; PAGES; 2010

Universidad de Valdivia

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 Sediment 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 detailed 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, conditions became moister with a concurrent lake level rise. Moderate salinities and the presence of abundant marginal vegetation are inferred from ostracods and diatoms. At 2400 cal. BP changes in diatom and ostracod assemblages 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 relative 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 Interdisciplinary Project (PIPA) (PICTR 2006 – 2338) and includes neolimnological 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.