Southern Patagonian glacial chronology for the Last Glacial period and implications for Southern Ocean climate

摘要

The Magellan region of southern South America is in a unique setting, at > 50 degrees S on the equatorial side of the Antarctic Frontal Zone, to record in detail terrestrial glacial to interglacial events. A Be-10 chronology shows growth and millennial fluctuations of a Patagonian Ice Sheet between similar to 25 and 17.6-17.0 cal ka. In the Strait of Magellan, the maximum ice margin position is dated to 24.6 +/- 0.9 ka, and other moraine ages are 18.5 +/- 1.8 and 17.6 +/- 0.2 ka (mean +/- 1 standard deviation). In Bahia Inutil, dated moraine ages are 20.4 +/- 1.2 and 17.3 +/- 0.8 ka. The chronology of the local Last Glacial Maximum (LGM) reveals a record of atmospheric cooling that was broadly in phase with changes in Southern Ocean conditions, such as sea-ice fluctuations and surface water characteristics. Published modeling results indicate that a decline in temperature of similar to 6 degrees C and slight drying over southernmost Patagonia could simulate the growth and sustained presence of an ice sheet to the mapped LGM limit. The terrestrial record in southern Patagonia and marine records in adjacent oceans indicate mean northward movement of the Antarctic Frontal Zone, which caused the last southern South American ice age. The Antarctic Frontal Zone at present lies only 3-5 degrees to the south. Some significant changes in the Magellan region occurred in step with North Atlantic region and the Northern Hemisphere. For example, the overall time span of the last glaciation and the timing of maximum ice extent were similar between the hemispheres, despite maximum local summer insolation intensity in southern South America. Other characteristics of the southern Patagonian glacial history differ from the North Atlantic region, specifically an out-of-phase relationship during deglaciation, which is more similar to that of Southern Ocean and Antarctic records. (C) 2007 Elsevier Ltd. All rights reserved.