Termination of the last ice age in the mid-latitudes of South America.

摘要

Pollen stratigraphies from Canal de la Puntilla {dollar}(40spcirc57spprime{dollar}S, {dollar}72spcirc54spprime{dollar}W), Huelmo {dollar}(41spcirc31spprime{dollar}S, {dollar}73spcirc00spprime{dollar}W), and Lago Condorito {dollar}(41spcirc45spprime{dollar}S, {dollar}73spcirc07spprime{dollar}W) show the presence of a Nothofagus dombeyi-type parkland and Magellanic Moorland taxa in the Southern Chilean Lake District between 15.8-14.6 kyr (*10{dollar}sp3 sp{lcub}14{rcub}{dollar}C yr B.P.), indicating glacial maximum conditions. An abrupt increase of Nothofagus dombeyi-type at {dollar}sim{dollar}14.6 kyr represents the early response of the local vegetation to a warming event that marked the onset of the last termination. This warming led to the abrupt withdrawal of Andean ice lobes from the Chilean Lake District and Isla Grande de Chiloe. Subsequent warming at 14.2 kyr led to the abrupt expansion of North Patagonian Rain Forest taxa, followed by the expansion of closed-canopy North Patagonian Rain Forest vegetation at {dollar}sim{dollar}13 kyr, and the disappearance of subantarctic, high Andean, and Magellanic Moorland taxa. These vegetation changes suggest both a warming event and reduction in annual precipitation at {dollar}sim{dollar}13 kyr. Conditions slightly cooler and wetter than modern-day climate persisted between {dollar}sim{dollar}13 and {dollar}sim{dollar}12.2 kyr. The expansion of cold-resistant taxa at {dollar}sim{dollar}12.2 and {dollar}sim{dollar}11 kyr, a decline in thermophilous species, and the spread of Nothofagus dombeyi-type at {dollar}sim{dollar}11 kyr all indicate a reversal, with cooling events at {dollar}sim{dollar}12.2 and {dollar}sim{dollar}11 kyr. Subsequent warming occurred at 9.9 kyr.; The data presented in this thesis, along with glacial geological studies from the Chilean Lake District, differ significantly from published Antarctic ice-core records from Byrd and Vostok in: (i) the onset of the last termination (17.5 kcal ({dollar}sim{dollar}14.6 kyr) versus 20.2 kcal ({dollar}sim{dollar}17.1 kyr)), (ii) the rate of temperature recovery to modern-day conditions, (iii) the direction (warming versus cooling during the ACR), and (iv) frequency of climate changes. In contrast, our results are most similar to paleoclimate records from the Northern Hemisphere (onset of the last termination at 14.7 kyr; Bolling-age warming; Older- and Younger Dryas-cooling; and Preboreal-age warming), suggesting that the Southern Ocean may have imposed a regional signal at high latitudes in the Southern Hemisphere that overrode the global termination of the last ice age.