The timing of the last glacial maximum in Australia

Barrows, T. T.¹, Stone, J. O.², Fifield, L. K.³, and Cresswell, R. G.³

1. Research School of Earth Sciences, Austraian National University, ACT, 0200, Canberra (current address: NISTAAR, University of Colorado, campus Box 450, Boulder, CO USA 80309 barrows@spot.colorado.edu)
2. Quaternary Research Center and Department of Geological Sciences, Bos 351360, University of Washington, Seattle, 98195-1360, USA
3. Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, ACT, 0200, Canberra.

Only a small part of mainland Australia (12-15 km²) was glaciated during the last glacial maximum (LGM) (Barrows et al., in press a). Glaciation was much more extensive in Tasmania, and covered as much as 2000 km². Despite more than a century of research, the chronology of LGM glacial deposits in Australia has been restricted to a handful of ¹⁴C dates only. To place tighter constraints on the timing of the LGM, nearly 100 exposure ages were determined on glacial and preglacial landforms using the cosmogenic isotopes ³⁶Cl and ¹⁰Be. A glacial stratigraphy for southern Australia was then constructed from these ages. We found that the LGM type section in Tasmania, the Hamilton Moraine below Lake Margaret, is actually mid Pleistocene in age. The glacier advance of greatest extent during the LGM was the Blue Lake Advance of the Late Kosciuszko glaciation (LK_BL). Twenty three ages from eleven LK_BL equivalent moraines in seven regions were chosen to define the ages of this event (Barrows et al., in press b). Despite occurring over a region of 8° of latitude and 1500m of elevation in climatically different areas, there is no significant variation in the age of this advance across the region. The age according to ¹⁰Be is 17.3 ka and the age according to ³⁶Cl is 19.7 ka. The difference between these ages is believed to be due to errors in the scaled production ratesin one or both isotopes. A peak in periglacial activity occurs at 22.7 ka, dated using ³⁶Cl (Barrows et al., in preparation). In comparison, minium sea-surface temperatures occurred in the neighbouring southwest Pacific Ocean at 20.6 ka and the d ¹⁸O maximum occurred at 18.6 ka (Barrows, et al., 2000). The latter age post-dates the sea level minium and is believed to represent a lag in propagating the d¹⁸O signal into the Southern Hemisphere due to slower deep-water circulation during the LGM. The close correspondence between the mean age of the LK_BL advance and the peak of periglacial activity according to ³⁶Cl, existing ¹⁴C dates and the SST minimum suggests that the LGM was at its coldest in Southern Australia between 20-23 ka.

References:

Barrows, T. T., Juggins, S., De Deckker, P., Thiede, J. and Martinez, J. I. (2000). Sea-surface temperatures of the southwest Pacific Ocean during the last glacial maximum. Paleoceneanography, 15(1): 95-109.

Barrows, T. T., Stone, J. O., Fifield, L. K., and Cresswell, R. G. (in press a). Late Pleistocene glaciation of the Kosciuszko Massif, Snowy Mountains, Australia. Quaternary Research.

Barrows, T. T.¹, Stone, J. O.², Fifield, L. K.³, and Cresswell, R. G. (in press b). The timing of the last glacial maximum in Australia. Quaternary Science Reviews.