Paleoenviromental changes in the Última Esperanza area (51ºS) during the last glacial- interglacial transition, southern Chile
by
Macarena Luc Cárdenas
Universidad de Chile, Chile
Coauthors: Patricio I. Moreno(Departamento de Ciencias Ecológicas, Universidad de Chile)and Rodrigo Villa-Martínez(Universidad de Magallanes, Chile)

Pollen, microcharcoal, and stratigraphic analyses of lake sediments from the Eberhard site (51º34’39.4”S, 72º40’06.6”W, ~71 m elevation), allows a detailed examination of the last glacial-interglacial transition in the Seno de Última Esperanza area of SW Patagonia (17.7-8 ka, ka=103 calendar years AP). Ice recession following the Last Glacial Maximum began at 17.7 ka and led to the development of an ice dammed proglacial lake between 17.7-12.5 ka. The proglacial lake persisted until glacial recession in the Andes triggered a catastrophic outflow at 12.5 ka, evidenced as an abrupt transition from glaciolacustrine mud to organic and carbonate-rich lake sediments in the Eberhard site.

The pollen record shows the predominance of herbs, shrubs, and abundant microcharcoal between 12.5-11.9 ka, suggesting an open landscape and high incidence of fire under cold, dry conditions. An abrupt expansion of Nothofagus woodland/forest occurred at ~11.8 ka, suggesting an increase in temperature and precipitation. A brief reversal in trend ensued (between 11.7-11.5 ka), followed by forest reexpansion and increase in arboreal diversity starting at 9.2 ka. A prominent increase of Cyperaceae began at ~10.6 ka, indicative of a lake level drop, terrestrialization of its periphery, and decline in precipitation.

Steppe expansion and human occupations in the Última Esperanza area began immediately after the catastrophic drainage of the ice-dammed proglacial lake. Forests, on the other hand, expanded in discrete pulses at 11.8 and 11.5 ka. This delayed expansion coincides with the deposition of a discrete carbonate-rich, laminated unit confined to the interval between 12.7-11.5 ka. A possibility exists that high precipitation variability inhibited forest expansion and favored fire occurrence, suggesting that the southern westerlies may have experienced extreme, sub-millennial-scale variability during the Younger Dryas Chron. The demise of the Pleistocene megafauna in the study area occurred once forest expanded, at the end of an extremely variable climate interval.

Acknowledgements: Fondecyt #1040204, National Geographic Society #7416-03, Iniciativa Científica Milenio P02-051, CEQUA

Date received: November 19, 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-39.