Comparing Glacial‐Geological Evidence and Model Simulations of Ice Sheet Change since the Last Glacial Period in the Amundsen Sea Sector of Antarctica

Joanne S Johnson,Dylan H Rood,Joerg M Schaefer,Stephen J Roberts,David Pollard,Pippa L Whitehouse

doi:10.1029/2020jf005827

Abstract

AbstractSince the Last Glacial Maximum ∼20,000 years ago, the Antarctic Ice Sheet has undergone extensive changes, resulting in a much smaller present‐day configuration. Improving our understanding of basic physical processes that played important roles during that retreat is critical to providing more robust model projections of future retreat and sea‐level rise. Here, a limited‐area nested ice sheet model was applied to the last deglacial retreat of the West Antarctic Ice Sheet in the Amundsen Sea Embayment (ASE), at 5 km resolution. The ice sheet response to climate and sea‐level forcing was examined at two sites along the flowlines of Pine Island Glacier and Pope Glacier, close to the Hudson Mountains and Mount Murphy respectively, and the simulated responses compared with ice sheet thinning histories derived from glacial‐geological data. The sensitivity of results to selected model parameters was also assessed. The model simulations predict a broadly similar response to ocean forcing in both the central and eastern ASE, with an initial rapid phase of thinning followed by a slower phase to the modern configuration. Although there is a mismatch of up to 5,000 years between the timing of simulated and observed thinning, the modeling suggests that the upstream geological records of ice surface elevation change reflect a response to retreat near the grounding line. The model‐data mismatch could potentially be improved by accounting for regional variations in mantle viscosity, sea‐surface heights and basal sliding properties across the continental shelf.

Highlights

A limited-area nested ice sheet model was applied to the last deglacial retreat of the West Antarctic Ice Sheet in the Amundsen Sea Embayment (ASE), at 5 km resolution
The largest change in the configuration of the Antarctic Ice Sheet in the recent geologic past has been its retreat from Last Glacial Maximum (LGM) extent over the past ∼20,000 years
The timing of modeled thinning prior to the Holocene contrasts with the early- to mid-Holocene ice surface lowering suggested by the exposure age data, the similar response at both sites is consistent with a hypothesis that both Pine Island and Pope Glaciers were responding to similar forcing mechanisms

Summary

Introduction

The largest change in the configuration of the Antarctic Ice Sheet in the recent geologic past has been its retreat from Last Glacial Maximum (LGM) extent over the past ∼20,000 years During this time, grounding lines have retreated hundreds of kilometers across the continental shelf to their modern positions (RAISED consortium, 2014). Glacial-geological records of Antarctic ice sheet retreat since the Last Glacial Maximum (LGM) were comprehensively reviewed and synthesized in 2014 (RAISED consortium, 2014) These were deduced using methods such as radiocarbon dating of marine sediments, bathymetric and seismic surveys of submarine glacial bedforms, and cosmogenic nuclide surface exposure dating of terrestrial rock outcrops near modern ice margins. Grounding line retreat to near-modern positions during that time was probably driven by warming of sub-surface ocean water and an associated increase in sub-ice shelf melting (Golledge et al, 2013; Mackintosh et al, 2011; RAISED consortium, 2014)

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Conclusion