Average Pleistocene Climatic Patterns in the Southern Central Andes: Controls on mountain glaciation and Paleoclimate Implications

摘要

Despite elevations of 5000-6800 m, modern glaciers occur along the southern Puna Plateau and the northern Sierras Pampeanas in the southern central Andes. The modern snowline rises from 5100 m in Sierra Aconquija to 5800 m in the Puna as a result of a westward decrease in precipitation from 450 to less than 1 mm/yr. During the Pleistocene these arid highlands experienced multiple cirque and valley glaciation that likely postdate the last interglacial period, although lack of age control prevents an absolute chronology. Glaciation in the Puna and along the eastern Puna edge produced a 300-m Pleistocene snowline (PSL) depression, while in the Sierras Pampeanas the PSL depression was at least 900 m. the greater PSL depression in the Sierras Pampeanas is best explained by a combination of cooling and increase of easterly moisture, whereas the PSL depression in the Puna appears more sensitive to moisture increase than temperature. previously, glaciations in this region have been explained by increased precipitation, with a westward depression of the snowline caused by a northward shift of the Pacific anticyclone and equatorward shift of the westerlies. However these PSL results rquire an increase of moisture from the east rather than from the west. Further, analysis of topographic data indicates that drainage-basin relief decreases north of 28 deg S. The regional landscape response suggests that the circulation patterns currently observed have persisted at least during the Pleistocene and perhaps during the past several million years.