Past water flow beneath Pine Island and Thwaites glaciers, West Antarctica

James D Kirkham,Frank O Nitsche,Kelly A Hogan,Nicholas R Golledge,Julian A Dowdeswell,Robert D Larter,Neil S Arnold

doi:10.5194/tc-13-1959-2019

James D Kirkham, Frank O Nitsche + Show 5 more

Open Access

https://doi.org/10.5194/tc-13-1959-2019

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Abstract

Abstract. Outburst floods from subglacial lakes beneath the Antarctic Ice Sheet modulate ice-flow velocities over periods of months to years. Although subglacial lake drainage events have been observed from satellite-altimetric data, little is known about their role in the long-term evolution of ice-sheet basal hydrology. Here, we systematically map and model past water flow through an extensive area containing over 1000 subglacial channels and 19 former lake basins exposed on over 19 000 km2 of seafloor by the retreat of Pine Island and Thwaites glaciers, West Antarctica. At 507 m wide and 43 m deep on average, the channels offshore of present-day Pine Island and Thwaites glaciers are approximately twice as deep, 3 times as wide, and cover an area over 400 times larger than the terrestrial meltwater channels comprising the Labyrinth in the Antarctic Dry Valleys. The channels incised into bedrock offshore of contemporary Pine Island and Thwaites glaciers would have been capable of accommodating discharges of up to 8.8×106 m3 s−1. We suggest that the channels were formed by episodic discharges from subglacial lakes trapped during ice-sheet advance and retreat over multiple glacial periods. Our results document the widespread influence of episodic subglacial drainage events during past glacial periods, in particular beneath large ice streams similar to those that continue to dominate contemporary ice-sheet discharge.

Highlights

The widespread and accelerating retreat of Pine Island and Thwaites glaciers constitutes a potential threat to the stability of the West Antarctic Ice Sheet (WAIS) (Rignot et al, 2008, 2014; Joughin et al, 2014; Feldmann and Levermann, 2015; Shepherd et al, 2018; Yu et al, 2018)
Our numerical model produces similar steady-state discharges and filling and drainage timescales to those that are observed for subglacial lakes beneath the contemporary Antarctic Ice Sheet
The fluxes of water flowing in continuous steady state beneath the LGM ice sheet are too low to have formed channels of the scale observed in Pine Island Bay

Summary

Introduction

The widespread and accelerating retreat of Pine Island and Thwaites glaciers constitutes a potential threat to the stability of the West Antarctic Ice Sheet (WAIS) (Rignot et al, 2008, 2014; Joughin et al, 2014; Feldmann and Levermann, 2015; Shepherd et al, 2018; Yu et al, 2018). The routing, storage, and expulsion of subglacial water from beneath the WAIS directly influences its mass-loss rates and, sealevel rise (Joughin et al, 2002; Alley et al, 2006; Bell et al, 2007; Stearns et al, 2008). Variability in subglacial water supply can lead to ice-sheet instability (Schoof, 2010). Ice-penetrating radio–echo sounding surveys and satellite altimetry have revealed an intricate subglacial network of water storage and transfer beneath the contemporary Antarctic Ice Sheet. Over 400 ponded water bodies, termed subglacial lakes, have been detected beneath the ice (Fig. 1) The subglacial routing of the water released from this special class of “active” subglacial lakes can be traced for hun-

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