Southern Hemisphere millennial glaciations during the past 30 ka driven by Antarctic ice sheet variability
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Date
2010-02-01
Authors
Fink, D
Williams, P
Journal Title
Journal ISSN
Volume Title
Publisher
Compañía Impresora Meza Ltda
Abstract
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. 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. Five other glacial advance phases are recorded as distinct benches with ages decreasing with altitude from LGM peak (27.2 ka, 830 m a.s.l.), recessional phases (24.4, 19.9, 20.7 and 17.2 ka) with the youngest terrace just above the lake (15.8 ka, 220 m a.s.l.). 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. 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, Isotope dating, Moraines, Climatic change, Valleys
Citation
Fink, D., & Williams, P. (2010). Southern Hemisphere millennial glaciations during the past 30 ka driven by Antarctic ice sheet variability. Paper presented at the International Glaciological Conference (VICC 2010) - "Ice and Climate Change: A View from the South", 1st - 3rd February 2010. Valdivia, Chile: Centro de Estudios Científicos (CECS), (pp. 10).