Cold-dry vs Warm-wet events in the South American extratropics since the Last Glacial Maximum

PIOVANO, E.L., ARIZTEGUI, D., ZANOR

Fukuoka, Japón

Congreso; 17th International Sedimentological Congress; 2006

IAS

Recent weather patterns combined with results of high resolution paleostudies indicate that the role of tropical and subtropical areas may have been underestimated as forcing factors of changes within the global climate system. Thus, the study of well-constrained paleoenvironmental records in these regions became critical. Laguna Mar Chiquita (30°54´S-62°51´W) is a shallow saline lake in the subtropical Pampean plains of Argentina. Temporal variability of the hydrological balance shows dramatic lake-level fluctuations, highlighting Laguna Mar Chiquita sedimentary record as a sensitive climatic archive. During highstands, as at present, the lake ?with a surface of ca. 6,000 Km2- becomes not only the largest saline lake in South America but also one of the largest in the world. 210Pb ages from short-cores allowed correlating and calibrating the lake sedimentary, isotope and biological response to the last 100 years of documented lake levels changes. The comparison among these sedimentological and geochemical features, the stable isotope signals and the diatom record shows a coherent picture that further allows us to formulate a well constrained multiproxy model for the basin. The study of long sedimentary cores (4.20 m) allows the reconstruction of lake-level variations covering the hydrological changes that occurred in this area since the Last Glacial Maximum (LGM). The hydrological response during LGM, LIA and last three decades clearly indicate that dry conditions prevail during cold phases whereas wet conditions take place during warm periods. The 20th century sequence of variations in the hydrological balance of Laguna Mar Chiquita is synchronous and in phase with other hydrological changes observed in SE South American (SESA) rivers (e.g., Río Paraná) pointing towards that the reconstructed paleohydrology can be extrapolated to a wide region of SESA.