DEGLACIATION CHRONOLOGY OF THE EAST AND WEST ANTARCTIC ICE SHEETS

The inaccessibility of Antarctica, sparsity of outcrop, scarcity of fossil biotic carbon for C-14 dating, and the fact that the remaining ice sheet terminates in the ocean around most of its margin, all complicate study of the behavior of the Antarctic ice sheet through the last glacial maximum (LGM). Increasing research activity resulting from recognition of the importance of the southern hemisphere in the ice-age climate system, the advent of exposure dating with cosmogenic nuclides, and extensive marine geophysical mapping of the Antarctic shelf, have greatly increased our knowledge in the past decade.

Evidence on land indicates that: (i) The LGM in Antarctica culminated 5000-10,000 years after ice sheets in the Northern Hemisphere reached their maximum extent. (ii) The large, continental East Antarctic Ice Sheet (EAIS) and smaller, marine West Antarctic Ice Sheet (WAIS) grew and retreated out of phase with one another. (iii) Comparison with ice-core records shows that the response of both ice sheets lagged changes in surface temperature and snow accumulation by thousands of years. (iv) The paradigm that the extent of ice in Antarctica is controlled from the northern hemisphere, through the effect of boreal ice sheets on global sea level, is inadequate to explain the behavior of the WAIS, in particular, through the last termination. Grounded ice in the Ross Sea, Marie Byrd Land, and Weddell Sea continued to retreat into the late Holocene, a trend that may be continuing in these and other sectors of the WAIS at the present day. Late deglaciation of West Antarctica has important implications for modeling of global sea level change, and the establishment of modern patterns of ocean circulation.

To substantiate these conclusions, I will review cosmogenic nuclide deglaciation chronologies of East Antarctic sites in Lutzow-Holm Bay (39° E), the Prince Charles Mountains (60- 80° E), the Vestfold Hills (78° E), the Bunger Hills (101° E), and Vincennes Bay (111° E), and West Antarctic sites in Marie Byrd Land (145° W) and the Ellsworth Mountains (83° W).

Acknowledgements: This presentation summarises work with a very large number of collaborators. Supported by Australian ASAC awards and NSF grants OPP-9909776, 9909778, 0229915 and 0230198.