The hydrological and environmental evolution of shallow Lake Melincue, central Argentinean Pampas, during the last millennium

International audienceLake Melincue, located in the central Pampean Plains of Argentina, is a shallow (similar to 4 m), subsaline lake (TDS >2000 ppm), highly sensitive to hydrological changes. The modern shallow lake system is composed of: (a) a supralittoral area, which includes a narrow mudflat, a vegetated mudflat and wetlands subenvironments; and (b) the main water body, comprising lacustrine marginal and inner areas. The development and extension of these subenvironments are strongly conditioned upon lake surface fluctuations. Past environmental changes were reconstructed through sedimentological, physical and geochemical proxy analyses of two short sedimentary cores (similar to 127 cm). Well-constrained Pb-210 ages profiles were modeled and radiocarbon chronologies were determined, covering a period from similar to AD 800 to the present. The analyzed sedimentary cores from Lake Melincue allowed for the reconstruction of past hydrological scenarios and associated environmental variability, ranging from extremely low lake levels during dry phases to pronounced highstands at wet periods. The paleohydrological reconstruction revealed very shallow conditions in the period between AD 806 and AD 1880, which was registered by massive deposits with low organic matter. Relatively wetter phases disrupting this dry period were represented by organic matter increases. A major wet phase was registered by AD 1454, after the end of the Medieval Climate Anomaly. A subsequent abrupt shift from this wet phase to drier conditions could be matching the transition between the end of the Medieval Climatic Anomaly and the beginning of the Little Ice Age. The occurrence of sedimentary hiatuses between AD 1492 and AD 1880 in Melincue sequence could correspond to intensive droughts during the Little Ice Age. After AD 1880, banded and laminated, autochthonous, organic matter-rich sediments registered an important lacustrine transgression and the onset of a permanent shallow lake, corresponding to the beginning of the current warm period. The uppermost recent fine-grained, low salinity, organic sediments represent a lake transgression occurred in the 1970s, coeval with a general increase in precipitation across southeastern South America. This transgression is registered regionally in other Pampean lakes and in the 20th century instrumental records of Lake Melincue. This paleoenvironmental reconstruction provides a new high-resolution record that registers striking hydroclimatic changes occurred at a regional scale across the Pampean Plains during the last millennium and it contributes to understand the past climatic history in southeastern South America. (C) 2015 Elsevier B.V. All rights reserved