C024-02
Early- to mid-Holocene ice sheet thinning in the Pine Island-Thwaites Glacier catchment of West Antarctica: glacial-geological observations and modeling

Wednesday, 9 December 2020: 05:34
Virtual
David Pollard1, Joanne Johnson2, Stephen J Roberts2, Dylan H Rood3, Joerg Schaefer4, Pippa Whitehouse5, Brent M Goehring6, Louise Ireland2, Jennifer L Lamp7, Cari Rand8 and James Smith9, (1)Pennsylvania State University Main Campus, University Park, PA, United States, (2)NERC British Antarctic Survey, Cambridge, United Kingdom, (3)Imperial College London, London, SW7, United Kingdom, (4)Columbia University of New York, Lamont-Doherty Earth Observatory, Palisades, NY, United States, (5)Durham University, Department of Geography, Durham, United Kingdom, (6)Tulane University of Louisiana, Department of Earth and Environmental Sciences, New Orleans, LA, United States, (7)Lamont-Doherty Earth Observatory, Palisades, NY, United States, (8)Tulane University of Louisiana, New Orleans, LA, United States, (9)British Antarctic Survey, Cambridge, United Kingdom
Abstract:
Here we present a new deglacial chronology for Pope Glacier ‒ located in the Pine Island-Thwaites Glacier catchment of West Antarctica ‒ that provides evidence for rapid thinning during the early- to mid-Holocene. We compare this with glacial-geological records of thinning of the nearby Pine Island Glacier (PIG), and apply a high-resolution ice sheet model to the last deglacial retreat in this region to examine ice sheet response to climate and sea-level forcing at both sites.

The large ice streams draining this sector of the Antarctic ice sheet have experienced rapid acceleration of flow, retreat and thinning during the past few decades. However, their millennial-scale retreat history is poorly known, despite the reliance of several ice sheet and glacial-isostatic adjustment (GIA) models on such data for improving sea-level prediction from this critical region.

Mt Murphy, a large nunatak situated adjacent to Pope Glacier, is strewn with quartz-bearing erratic cobbles and boulders up to 893 m above present sea-level that provide evidence of former ice cover. Cosmogenic 10Be and in-situ 14C exposure dating on cobbles and bedrock samples yielded exposure ages from which we infer that the surface of Pope Glacier lowered by 560 m between 9‒6 ka, at an average rate of 0.13 ± 0.09/0.04 m yr-1. The lowering coincided with enhanced upwelling of warm Circumpolar Deep Water onto the continental shelf. This may have facilitated a reduction in ice shelf buttressing, simultaneously triggering thinning of Pope Glacier.

Comparison of the new data with existing records of deglaciation in the Hudson Mountains, adjacent to PIG, suggests broadly simultaneous ice thinning at both sites. Likewise, our ice sheet model simulations predict a broadly similar response to ocean forcing in both the central and eastern Amundsen Sea Embayment, with an initial period of rapid thinning followed by a slower phase to the modern configuration. We hypothesize that this was the result of both glaciers responding to similar (ocean) forcing mechanisms. We identified a mismatch between the observed and predicted timing of thinning (thinning occurs ~5,000 years too early in the model), which could be improved (perhaps even resolved) by more-sophisticated regional bedrock/GIA modeling that would change the sensitivity of the model response to forcing.

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