Postglacial vegetation, fire, and climate history along the eastern Andes, Argentina and Chile (lat. 41-55°S)

Abstract

The role of climate in shaping the postglacial history of Patagonia (41–55°S) east of the Andes is evident in new pollen and charcoal data from Mallín Fontanito (44.91oS, 71.57oW) and their comparison with other paleoenvironmental records in the region. Between 17,800–13,000 cal yr BP, evidence of heath-steppe vegetation with some Nothofagus and little fire activity at M. Fontanito suggest cold, dry conditions in early late-glacial time. From 13,000–7000 cal yr BP, increased Nothofagus pollen and charcoal levels imply expanding tree cover and more fires, consistent with warming. Between 7000 and 4000 cal yr BP, closed Nothofagus forest was established at M. Fontanito during a period of low fire activity and effectively wetter conditions than before. Fluctuations in pollen and charcoal levels after 4000 cal yr BP are consistent with increased submillennial climate variability. The environmental history at M. Fontanito is similar to other records from central Patagonia east of the Andes (44-50oS); however, differences in the timing of fires and human occupation suggest that pre-European burning was local in nature. At a regional scale, composited Nothofagus pollen abundance and charcoal data east of the Andes (41-55oS) reveal latitudinal differences in the timing of forest establishment and fire that relate to changes in the strength and position of the Southern Westerly Winds (SWW) through time. Notably, the SWW were south of their present position between 14,000 and 9000 cal yr BP, leading to dry conditions across the region. The present storm-track position was established after 7000 cal yr BP, when region-wide increases in precipitation occurred.