Details

Autor(en) / Beteiligte

• Kaplan, M R
• Moreno, P I
• Villa-Martinez, R P
• Kubik, P W

Titel

Timing and Structure of Glacial Fluctuations at the end of the Last Ice Age in SW Patagonia

Ist Teil von

• Eos (Washington, D.C.), 2006-12, Vol.87 (52)

Erscheinungsjahr

2006

Link zum Volltext

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• In the mid to high southern latitudes much of the controversy regarding synchrony or bipolar asynchrony has centered on late glacial time, especially in South America as it is one of the few land masses south of 45degS, outside Antarctica. To help resolve this controversy, and in general understand this important time interval, we studied in detail the timing, structure, and relative amplitude of climate changes during the late glacial period at 50degS in SW Patagonia. We combined two independent dating approaches including cosmogenic dating of moraines and radiocarbon of lake sediment cores, in addition to paleoecologic studies of key sections. We measured the 10Be concentrations in erratics from maximum and retreat glacial deposits from the Lago Nordenskj'old and R'io Paine ice lobes. The 10Be ages from the two areas indicate a maximum extent prior to ~13 ka (4 ages), followed by slightly less extensive but sustained ice until ~12-11pm1 ka. Excluding ages from deposits clearly related to retreat, the mean 10Be age for the two lobes falls between 13-12 ka, and the maximum ages from the two areas are 14.3pm1.1 and 13.8pm1.8 ka, respectively. This timing agrees well with minimum 14C ages for glacial geomorphic features associated with the maximum and retreat ice positions. We interpret the onset of organic sedimentation in the area occupied by a former ice- dammed lake at 12.6 cal ka as the closest minimum age for ice recession from the maximum ice extent. The pollen data indicate extreme cold conditions between 14.8-12.5 ka, slight amelioration between 12.5-10.9 ka, followed by warming in the early Holocene Period. We conclude that 1) a major cold reversal took place in SW Patagonia overlapping in time with the Antarctic Cold Reversal and 2) ice retreated slowly but lingered close to the maximum position throughout Younger Dryas time until ~10.7pm0.9 ka under cold and, possibly, wet conditions. We speculate that southern latitude air-ocean dynamics, such as that of the Antarctic Polar Front, influenced the relative magnitude of these two prominent cold reversals at the end of the last ice age, in southernmost South America.