Holocene thinning and grounding-line retreat of Darwin andHatherton Glaciers, Antarctica

Abstract. We present exposure ages of glacial deposits at three locations alongside Darwin Glacier and its tributary Hatherton Glacier that record several hundred meters of late Pleistocene to early Holocene thickening relative to present. As the grounding-line of the Ross Sea Ice Sheet retreated rapidly southward, Hatherton Glacier thinned steadily from about 9 kyr BP until about 3 kyr BP. Our data are equivocal about the maximum thickness and mid-to-early Holocene history at the mouth of Darwin Glacier, allowing for two possible deglaciation scenarios: (1) ~500 m of steady thinning from 9 kyr BP to 3 kyr BP, similar to Hatherton Glacier, or (2) ~950 m of thinning, with a rapid pulse of ~600 m thinning at around 5 kyr BP. We test these two scenarios using a 1.5-dimensional flowband model of Darwin and Hatherton Glaciers, forced by ice-thickness changes at the mouth of Darwin Glacier and evaluated by fit to the chronology of deposits at Hatherton Glacier. Our modeling shows that the constraints from Hatherton Glacier are consistent with the interpretation that the mouth of Darwin Glacier thinned steadily by ~500 m from 9 kyr BP to 3 kyr BP; rapid pulses of thinning at the mouth of Darwin Glacier are ruled out by the data at Hatherton Glacier. This contrasts with some of the available records from the mouths of other outlet glaciers in the Transantarctic Mountains, many of which thinned by hundreds of meters over roughly a one-thousand-year period in the early Holocene. The deglaciation histories of Darwin and Hatherton Glaciers are best matched by a steady decrease in catchment area through the Holocene, suggesting that Byrd and/or Mulock glaciers may have captured roughly half of the catchment area of Darwin and Hatherton Glaciers during the last deglaciation. An ensemble of three-dimensional ice-sheet model simulations suggest that Darwin and Hatherton Glaciers are strongly buttressed by convergent flow with ice from neighboring Byrd and Mulock glaciers, and by lateral drag past Minna Bluff, which could have led to a pattern of retreat distinct from other glaciers throughout the Transantarctic Mountains.