Abstract

AbstractIn the Amundsen sector of West Antarctica, the flow of glaciers accelerates when intrusion of warm ocean water onto the continental shelf induces strong melting beneath ice shelves and thinning near the glaciers' grounding line. Predicting the future of these glaciers is, however, hindered by a poor understanding of the dynamical processes that may exacerbate, or on the contrary modulate, the inland ice sheet response. This study seeks to investigate processes occurring at the base of Pine Island Glacier through numerical inversions of surface velocities observed in 1996 and 2014, a period of time during which the glacier accelerated significantly. The outputs show that substantial changes took place in the basal environment, which we interpret with models of undrained subglacial till and hydrological routing. The annual basal melt production increased by 25% on average. Basal drag weakened by 15% over nearly two thirds of the region of accelerated flow, largely due to the direct assimilation of locally produced basal meltwater into the underlying subglacial sediment. In contrast, regions of increased drag are found to follow several of the glacier's shear margins and furthermore to coincide with inferred hydrological pathways. We interpret this basal strengthening as signature of an efficient hydrological system, where low‐pressure water channels have reduced the surrounding basal water pressure. These are the first identified stabilization mechanisms to have developed alongside Pine Island ice flow acceleration. Indeed, these processes could become more significant with increased meltwater availability and may limit the glacier's response to perturbation near its grounding line.

Highlights

  • Pine Island Glacier (PIG) is a fast‐flowing glacier, which drains the West Antarctic Ice Sheet

  • The causes of the dynamical changes observed near the grounding line of PIG have been widely attributed to oceanographic conditions (Dutrieux et al, 2014; Jacobs et al, 2011; Jenkins et al, 2010; Payne et al, 2004; Steig et al, 2012), with inflow of relatively warm circumpolar deep water increasing basal melting of its ice shelf (Jacobs et al, 1996)

  • Using the difference in basal drag between 1996 and 2014 as a means to estimate changes in till water storage (equation (5)), we find that flow of water into the till layer is around two orders of magnitude smaller than the volume of water produced by basal melting

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Summary

Introduction

Pine Island Glacier (PIG) is a fast‐flowing glacier, which drains the West Antarctic Ice Sheet. The causes of the dynamical changes observed near the grounding line of PIG have been widely attributed to oceanographic conditions (Dutrieux et al, 2014; Jacobs et al, 2011; Jenkins et al, 2010; Payne et al, 2004; Steig et al, 2012), with inflow of relatively warm circumpolar deep water increasing basal melting of its ice shelf (Jacobs et al, 1996). The rate of flow acceleration near the grounding line has decreased (Joughin et al, 2010; Shen et al, 2018), yet PIG remains out of balance and the inland flow continues to experience acceleration and thinning, albeit at rates varying considerably over the extent of the glacier (Konrad et al, 2017). It has been suggested that this heterogeneous ice flow evolution may be due to Journal of Geophysical Research: Earth Surface

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