Abrupt vegetation changes during the last glacial to Holocene transition in mid-latitude South America

A pollen record from the Huelmo site (ca. 41degrees30'S) shows that vegetation and climate changed at millennial time-scales during the last glacial to Holocene transition in the mid-latitude region of western South America. The record shows that a Nothofagus parkland dominated the landscape between 16400 and 14 600 C-14 yr BP, along with Magellanic Moorland and cupressaceous conifers. Evergreen North Patagonian rainforest taxa expanded in pulses at 14200 and 13000 C-14 yr BP, following a prominent rise in Nothofagus at 14600 C-14 yr BP. Highly diverse, closed canopy rainforests dominated the lowlands between 13000 and 12500 C-14 yr BP, followed by the expansion of cold-resistant podocarps and Nothofagus at ca. 12500 and 11500 C-14 yr BP. Local disturbance by fire favoured the expansion of shade-intolerant opportunistic taxa between 10900 and 10200 C-14 yr BP. Subsequent warming pulses at 10200 and 9100 C-14 yr BP led to the expansion of thermophilous, summer-drought resistant Valdivian rainforest trees until 6900 C-14 yr BP. Our results suggest that cold and hyperhumid conditions characterised the final phase of the Last Glacial Maximum (LGM), between 16400 and 14600 C-14 yr BP. The last ice age Termination commenced with a prominent warming event that led to a rapid expansion of North Patagonian trees and the abrupt withdrawal of Andean ice lobes from their LGM positon at ca. 147000 C-14 yr BP. Hyper-humid conditions prevailed between 16400 and 13000 C-14 yr BP, what we term the 'extreme glacial mode' of westerly activity. This condition was brought about by a northward shift and/or intensification of the southern westerlies. The warmest/driest conditions of the last glacial-interglacial transition occurred between 9100 and 6900 C-14 yr BP. During this period, the westerlies shifted to an 'extreme interglacial mode' of activity, via a poleward migration of stormtracks. Our results indicate that a highly variable climatic interval lasting 5500 C-14 years separate the opposite extremes of vegetation and climate during the last glacial-interglacial cycle, i.e. the end of the LGM and the onset of the early Holocene warm and dry period. Copyright (C) 2003 John Wiley Sons, Ltd.