CONTRASTING HYDROCLIMATE CONDITIONS IN THE ARGENTINEAN PAMPEAN PLAINS: THE PALEOLIMNOLOGICAL RECORD OF THE LITTLE ICE AGE AND THE 20TH CENTURY

LUCÍA GUERRA; EDUARDO PIOVANO

Valdivia

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

Centro de Estudios Científicos de Valdivia (CECS)

Limnogeological reconstructions, in addition to historical data, indicate two recent contrasting hydroclimatic phases overall the Pampean Plains: a cold and dry period ascribed to the Little Ice Age (LIA) and a hyper-humid stage after the decade of 1970s. Throughout the late Holocene, different shallow lakes in the central plains of South Eastern South America (SESA) have registered synchronous behavior in their paleohydrological balance triggered by changes in the Precipitation-Evaporation ratio. In Laguna Mar Chiquita (30°54’S-62°51’W), limnogeological reconstructions suggest very dry conditions during the LIA. In agreement, historical evidence of Laguna Melincué (33°43’S-61°28’W) which is located further south in the same region, show pervasive arid conditions during the last part of the 18th century. For instance, chronicles of 1796 reveal that Laguna Melincué was separated in two minor water bodies denoting extremely low water-levels. Paleolimnological and instrumental records of Laguna Melincué suggest important water level fluctuations throughout the 20th century. The first decades are recorded by low lake level facies, indicating an arid period, which is followed by alternating humid/dry phases. A shift to a comparatively wetter scenario (registered on both, sedimentary and instrumental records) started in the Pampean plains during the decade of 1970 and it is still present. The observed contrasting hydrological situations during the LIA and 20th century on Pampean lakes indicate important climatic variations over the region and validate the hypothesis of the South America Monsoon like-system as the common mechanism controlling hydroclimatic variability in SESA, at least since late Holocene.