Southern Hemisphere millennial glaciations during the past 30 ka driven by Antarctic ice sheet variability
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Date
2009-05-15
Journal Title
Journal ISSN
Volume Title
Publisher
GNS Science
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.
Description
Keywords
Tasmania, New Zealand, Glaciers, Antarctica, Ice, Pleistocene epoch, Southern Hemisphere, Northern Hemisphere, Altitude
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.