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Title: Southern Hemisphere millennial glaciations during the past 30 ka driven by Antarctic ice sheet variability
Authors: Fink, D
Williams, P
Augustinus, P
Schulmeister, J
Keywords: Tasmania
New Zealand
Pleistocene epoch
Southern hemisphere
Northern hemisphere
Issue Date: 15-May-2009
Publisher: GNS Science
Citation: Fink., D., Williams, P., Augustinus, P., & Schulmeister, J. (2009). Southern Hemisphere millennial glaciations during the past 30 ka driven by Antarctic ice sheet variability. Paper presented at the Past Climates meeting, Wellington New Zealand, May 15-17, 2000.
Abstract: Recent exposure dating of last-glacial cycle deposits in Tasmania, New Zealand and Patagonia reveal a temporal and spatial variability of glacial advances different to that apparent in the Northern Hemisphere. Interhemispheric correlation of millennial-scale glaciations is presently the centre of much debate (e.g., Younger Dryas (YD) versus Antarctic Cold Reversal (ACR) cooling, timing of ‘global’ Last Glacial Maximum (LGM), relative strength of MIS-2 to MIS-6 glaciations). However, the role of Antarctica in Southern Hemisphere glaciations during the late Pleistocene is difficult to assess. Exposure ages from six alpine valley systems in Tasmania and three in New Zealand reveal similar trends: (1) MIS-3 (~30-40 ka) advances are of limited extent in Tasmania and less extensive than New Zealand MIS-2 advances; (2) peak glacial cold conditions (‘LGM’) occur between ~24-29 ka; (3) amelioration of LGM conditions and glacial retreat commenced ~19-22 ka; (4) deglaciation inferred from recessional moraine sequences continued to 14-15 ka; (5) there is little evidence for a major late glacial readvance younger than 14-15 ka with lower valley regions devoid of ice. This moraine chronology suggests that following a ‘weak’ MIS 3 cool phase, the Southern Hemisphere, or ‘local’ LGM, peaked and was followed by warming a few thousand years prior to that apparent in the Northern Hemisphere. These moraine ages from New Zealand and Tasmania for the LGM–LGIT (ca 30 to 11 ka) show a remarkable similarity to the glacial chronology emerging from Lagos Buenos Aires in Patagonia. A near-complete record of glacial expansion phases over the last glacial cycle is preserved in the series of 10 glacial moraine benches (8 of which have been exposure dated) that flank the slopes of Mt Murchison above Lake Te Anau, Fiordland, New Zealand. The ages span from 15-80 ka with the highest bench dated to MIS 4 (ca 65- 75 ka) and suggests that MIS 4 may have generated by far the largest glacial expansion of the last glacial cycle. Five other glacial advance phases are recorded as distinct benches with ages decreasing with altitude from LGM peak (27.2 ka, 830masl), recessional phases (24.4, 19.9, 20.7 and 17.2 ka) with the youngest terrace just above the lake (15.8 ka, 220 masl). This deglaciation chronology correlates well with δ18O variability apparent in the ice core records from Byrd and Law Dome in Antarctica, each of which display most depleted δ18O values from 30 to 20 ka, followed by general warming to 10 ka. Over this period, Byrd displays δ18O inferred cooling at 29, 27 and 22 ka, with hiatuses in warming at 18.9, 17.8, 16.8 and 15.9 ka. The latter phases can be matched to the Te Anau exposure dated moraine benches with an ca 1-3 ka delay between the polar warming phases and response of the Fiordland glaciers. Hence, the general character of Antarctic climate variability as observed in δ18O trends from the ice cores appear to be reflected in the Southern Hemisphere mid-latitude terrestrial deglaciation chronologies determined by cosmogenic exposure dating.
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