Thickness of the divide and flank of the West Antarctic Ice Sheet through the last deglaciation

We report cosmogenic-nuclide measurements from two isolated groups of nunataks in West Antarctica: the Pirrit Hills, located midway between the grounding line and the divide in the Weddell Sea sector, and the Whitmore Mountains, located along the Ross-Weddell divide. At the Pirrit Hills, ice reached a highstand ~ 320 m above present during the last glacial period. Subsequent thinning mostly occurred after ~ 14 kyr B.P., and modern ice levels were established some time after ~ 4 kyr B.P. We infer that, like at other flank sites, these changes were primarily controlled by the position of the grounding-line downstream. At the Whitmore Mountains, cosmogenic 14C concentrations in bedrock surfaces demonstrate that ice there was no more than ~ 190 m thicker than present during the past ~ 30 kyr. Combined with other constraints from West Antarctica, the 14C data imply that the divide was thicker than present for a period of less than ~ 8 kyr within the past ~ 15 kyr. These results are consistent with the hypothesis that the divide initially thickened due to the deglacial rise in snowfall, and subsequently thinned in response to retreat of the ice-sheet margin. We use these data to evaluate several recently-published ice-sheet models at the Pirrit Hills and Whitmore Mountains.