Decadal record of hydrological changes in subtropical South America of Central Argentina over the last 200 years
by
Florence Sylvestre
CEREGE-CNRS UMR 6635, Europôle de l'Arbois BP 80 13545, Aix-en-Provence cedex 04, France
Coauthors: Eduardo L. Piovano (Centro de Investigaciones Geoquímicas y de Procesos de Superficie, University of Córdoba, Argentina) and Daniel Ariztegui Institute F. A. Forel and Dept. of Geology and Paleontology, University of Geneva, Rue des Maraichers 13, CH-1205 Geneva, Switzerland.

Laguna Mar Chiquita, a highly variable closed saline lake located in the Pampean plains of central Argentina (30°54’S-62°51’W) provides a very suitable environment to study the biological response to dramatic lake level fluctuations. We developed a calibration dataset (transfer functions) for biological remains such as diatoms. These dataset was built using modern chemical data coupled with a combination of historical and instrumental information as well as the results of an in-depth sedimentological and isotopic study of well-dated cores. The fossil diatom study was conduced on a 1.15 m-long core collected from the deepest part of the lake and dated using a high-resolution 210Pb ages model. The diatom assemblages show two distinctive phases. Mesosaline to hypersaline periphytic taxa dominate from the bottom of the core (A.D. 1767) to A.D. 1973 indicating a shallow lake with a salinity averaging 77 g.L-1. This interval is interrupted by brief phases dominated by planktonic taxa indicating comparatively higher lake-level between A.D. 1850 and A.D. 1870. A major shift on the diatom assemblages occurred since A.D. 1973 that changed from periphytic- to planktonic-dominated taxa. This abrupt is recorded by a decrease of the salinity varying between 25 and 33 g.L-1. This second phase corresponds to an instrumentally-recorded highstand of the lake.

There is a striking correlation between the last 200 years of hydrological history as reconstructed by diatom assemblages and previous results of a multiproxy study of sedimentary cores. This agreement confirm that dry conditions were mostly dominant since A.D. 1767 (final stage of the Little Ice Age, LIA) until the last quarter of the 20th century, briefly interrupted by humid phases at the second half of the 19th century (A.D. 1850-1870). Since the 70’s, the lake reached its highest level of the last 230 years. Furthermore, the synchronicity between the lake-level fluctuations, the regional hydrological changes, and the streamflow of the rivers from the Rio de La Plata basin suggest that the hydrological changes recorded from Laguna Mar Chiquita reflect large-scale atmospheric mechanisms (e.g. SACZ) forcing the climatic variability, affording the opportunity to gain insight into paleo-circulation dynamics in subtropical South America during the Holocene.

Date received: December 10, 2004

Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caod-61.