Short Name:

EXPROBE-WAIS: Exposed Rock Beneath the West Antarctic Ice Sheet, A Test for Interglacial Ice Sheet Collapse

This award supports a project to determine if the West Antarctic Ice Sheet (WAIS) has thinned and collapsed in the past few million years, and if so, when and how frequently this occurred. The principal aim is to identify climatic conditions or thresholds in the climate system that led to ice-sheet collapse in the past, and assess the threat of climate change to vulnerable ice sheets in the future. We recovered a subglacial bedrock core from beneath 150 m of ice cover in the Pirrit Hills, in West Antarctica, and measured cosmogenic nuclide profiles to determine the bedrock exposure history. Cosmic-ray-produced Be-10 and Al-26 in the core indicate: (i) Continuous Pleistocene ice cover averaging ~200 m; and (ii) One or more pre-Pleistocene deglaciations that exposed the core site for ~200-800 years in the Pliocene, or > 800 years, in the Miocene. Optically stimulated luminescence (OSL) dating of the core top precludes exposure to sunlight since ~450 ka, consistent with the Be-10 and Al-26 data. Trapped atmospheric argon in ice recovered from 80 cm above the bedrock surface indicates an age for the enclosing ice > 2 Ma (delta 40Ar/36Ar = -0.15 per-mil). Together, these results rule out any Pleistocene thinning of ice in the Pirrit Hills by more than 150 m.

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