Vegetation history and climatic variability during the Late Holocene at Pampa grasslands: the state of the art

PRIETO, A. R.; STUTZ, S; VILANOVA, I.; TONELLO, M. S.

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

At Pampa grasslands (34º - 39º S; 56º - 63º W) the vegetational history based on pollen analysis has been mainly conducted at alluvial sites since pollen records from shallow lakes are temporally and spatially limited. Even though pollen assemblages in alluvial sequences may be biased as a result of episodic and irregular accumulation of sediments, these sequences are amazingly constant over large distances and contain very well preserved pollen grains in large quantities giving us the possibility to obtain important paleoenvironmental information. In this overview, we selected key proxy palynogical records with different temporal and spatial resolution in order to evaluate the response of the vegetation to different forcings during the late Holocene and to show the advancements achieved over the last years. The vegetation changes are discussed at individual sites by comparing them with other paleoenvironmental proxy and historical data. A quantitative climatic reconstruction applying a pollen-climate calibration model is presented and discussed as an example of quantification of paleoclimatic variables. Pollen records allowed us to infer (1) a pattern of environmental variability to large-scale, mainly in precipitation and humid index during the late Holocene, (2) sea level variations as the main forcing affecting the vegetation of the southeastern coast between 6500 and 4000 yr B.P and, (3) anthropogenic impact on vegetation over the last 300 years, which correlate accurately with evidence concerning the documentary information. In addition, pollen and no-pollen palynomorph records have recently allowed to propose an alternative explanation for the vegetational change from shallow lakes.