a1 Gateway Antarctica, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
a2 Institute for Environmental Research, ANSTO, PMB1, Menai 2234, Australia
a3 Geography, Planning and Environmental Management, University of Queensland, St Lucia 4072, Australia
a4 South Australian Museum, SA 5000, and School of Earth and Environmental Sciences, University of Adelaide, SA 5000, Adelaide, Australia
We present direct terrestrial evidence of ice volume change of the Darwin and Hatherton glaciers which channel ice from the Transantarctic Mountains into the Ross Ice Shelf. Combining glacial geomorphology with cosmogenic exposure ages from 25 erratics indicates a pre-LGM ice volume at least 600 m thicker than current Hatherton ice elevation was established at least 2.2 million years ago. In particular, five erratics spread across a drift deposit at intermediate elevations located below a prominent moraine feature mapped previously as demarcating the LGM ice advance limits, give a well-constrained single population with mean 10Be age of 37.0 ± 5.5 ka (1σ). At lower elevations of 50–100 m above the surface of Lake Wellman, a further five samples from within a younger drift deposit range in exposure age from 1 to 19 ka. Our preferred age model interpretation, which is partly dependent on the selection of a minimum or maximum age-elevation model, suggests that LGM ice volume was not as large as previously estimated and constrains LGM ice elevation to be within ± 50 m of the modern Hatherton Glacier ice surface, effectively little different from what is observed today.
(Received March 09 2010)
(Accepted August 30 2010)