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

Spector, Perry; Stone, John; Goehring, Brent

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, evidence of glacial-stage ice cover extends inline-formula∼320 m above the present ice surface. Subsequent thinning mostly occurred after inline-formula∼14 kyr BP, and modern ice levels were established some time after inline-formula∼4 kyr BP. 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 inline-formula14C concentrations in bedrock surfaces demonstrate that ice there was no more than inline-formula∼190 m thicker than present during the past inline-formula∼30 kyr. Combined with other constraints from West Antarctica, the inline-formula14C data imply that the divide was thicker than present for a period of less than inline-formula∼8 kyr within the past inline-formula∼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. Most of the models we consider do not match the observed timing and/or magnitude of thickness change at these sites. However, one model performs relatively well at both sites, which may, in part, be due to the fact that it was calibrated with geological observations of ice-thickness change from other sites in Antarctica.

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Spector, Perry / Stone, John / Goehring, Brent: Thickness of the divide and flank of the West Antarctic Ice Sheet through the last deglaciation. 2019. Copernicus Publications.

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