T15 Timing and Nature of Mountain Glacier Advances throughout the Last Glacial Cycle

Sunday, 16 October 2005
8:00 AM - 12:00 PM

ARE GLACIAL CHRONOLOGIES ACROSS THE SOUTHERN HEMISPHERE OVER THE PAST 80KA REGIONALLY SYNCHRONISED?

Paper number: T15-6
Program: Technical Sessions
Time: 9:15 AM – 9:30 AM

Authors

Abstract

Correlations of millennial-scale glacial transitions across Earth's hemispheres are presently the centre of much debate. Issues such as synchronicity or otherwise of Younger Dryas cooling prevalent in the Northern Hemisphere, the determination of a ‘global' nature for the Last Glacial Maximum, and linkages of continental glacial and ocean records are key questions in understanding the teleconnections of past global climate change. These issues are now being addressed within a Southern Hemisphere perspective based on cosmogenic exposure dating using 10Be and 26Al in alpine moraine systems. Our exposure-age data sets from numerous recessional and advance moraine sequences in Tasmania and New Zealand covering altitudes from 200 to 1200 masl plus new data from Patagonia (Kaplan et al, 2004) indicate : (1) no strong evidence to support a significant glacial readvance commensurate with the YD chronozone suggesting that Late Glacial (during the LGIT) amelioration of warming was weak ; (2) no proximal or cirque moraines younger than 15 ka indicating most major ice sources had dissipated 2-3 ka earlier in the Southern Hemisphere with the initiation of an abrupt warming phase; (3) a definitive, common age for the LGM remains elusive though it appears that peak glacial conditions were at 25-27 ka; (4) dissipation of LGM conditions commenced at ~19-20 ka and continued unabated to 14-15ka; (5) The extent of MIS 2 (local LGM) in Tasmania appears less than that in New Zealand and (6) the deglaciation sequence from 25 ka to 15 ka is remarkably similar between New Zealand and Patagonia

A near-complete record of the last glacial cycle is preserved in a series of 10 glacial lateral terraces that flank the slopes of Mt Murchison along Lake Te Anau (South Island, NZ). The highest terrace dates to MIS-4 (65-75 ka) and suggests that MIS-4 may have been by far the largest glacial stadial during the last glacial cycle. Five other glacial advances are recorded as distinct terraces with ages decreasing monotonically with altitude from 830 to 220 masl (27.1 ka, 24.4 ka, 20.9 ka, 17.2 ka and 15.8 ka). This post-LGM recessional deglacial chronology correlates with del-18O in ice core records from Byrd and Law Dome in Antarctica. Older dated glacial formations (MIS4 - MIS12) exhibit little correlation amongst alpine valley sites across mid SH latitudes.