Late Holocene quantitative paleoclimatic reconstruction from pollen records at Pampa grasslands

TONELLO, M. S.; PRIETO, A. R.

Malargue

Simposio; Simposio Internacional "Reconstrucciones Regionales de las Variaciones Climáticas en América del Sur durante el Holoceno tardío: Una nueva iniciativa de PAGES"; 2006

PAGES (Past Global Changes), International Geosphere-Biosphere Programme, Bern, Switzerland - Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), Mendoza, Argentina. - University of Bern, Bern, Switzerland.-

The Pampa grasslands are the most extensive region covered by grasses in Argentina (32º - 39º S). These grasslands represent one of the highest diversity grasslands in the world and their distribution is climatically determined. Nowadays, natural grasslands are partially substituted for agroecosystems since the region has an important economic value. Accurate reconstructions of late Holocene climate are needed to better understand the grasslands response to climate change. Using a calibration modern pollen-climate data set, two late Holocene fossil pollen records [Empalme Querandíes (EQ), in central Pampa grasslands and Sauce Chico (SCh), in the southwest boundary of Pampa grasslands] are interpreted in terms of mean annual precipitation (MAP) and annual humid index (AHI) by applying the modern analogue technique. During the last 3000 14C yrs B.P estimated MAP and IHA values in EQ showed fluctuations of ca. 100 mm around the modern values. Estimated MAP and IHA values in SCh showed fluctuations of high frequency (200 to 300 mm) between ca. 4500 and ca. 1500 14C years B.P. These values become higher than modern ones (up to 200 mm) between ca. 1500 and 1000 14C years B.P. and decreased (up to 100-150 mm) during the last ca. 500 14C years B.P. The reconstruction shows significant variability in the hydric regimen (MAP and AIH) during the late Holocene and the recent establishment of the modern climatic conditions. Further improvement of these quantitative reconstructions and an adequate chronological control for a meaningful correlation will allow testing the existence of a regional large-scale climatic variability.