Simulated dynamic regrounding during marine ice sheet retreat

Lenneke M Jong,Benjamin K Galton-Fenzi,Rupert M Gladstone,Matt A King

doi:10.5194/tc-12-2425-2018

Abstract

Abstract. Marine-terminating ice sheets are of interest due to their potential instability, making them vulnerable to rapid retreat. Modelling the evolution of glaciers and ice streams in such regions is key to understanding their possible contribution to sea level rise. The friction caused by the sliding of ice over bedrock and the resultant shear stress are important factors in determining the velocity of sliding ice. Many models use simple power-law expressions for the relationship between the basal shear stress and ice velocity or introduce an effective-pressure dependence into the sliding relation in an ad hoc manner. Sliding relations based on water-filled subglacial cavities are more physically motivated, with the overburden pressure of the ice included. Here we show that using a cavitation-based sliding relation allows for the temporary regrounding of an ice shelf at a point downstream of the main grounding line of a marine ice sheet undergoing retreat across a retrograde bedrock slope. This suggests that the choice of sliding relation is especially important when modelling grounding line behaviour of regions where potential ice rises and pinning points are present and regrounding could occur.

Highlights

Marine ice sheets, which are grounded below sea level, have been identified as having the potential to contribute significantly to future sea level rise through the rapid loss of ice under changing climate conditions
It has been suggested (Mercer, 1978; Weertman, 1974) that, when they are grounded on a retrograde-sloping bedrock, the positive relationship between ice thickness and ice flux leads to a positive feedback in which rapid retreat of the grounding line may occur, termed “marine ice sheet instability” (MISI)
MISI theory predicts that the grounding line of a glacier cannot stabilise on a retrograde bedrock slope

Summary

Introduction

Marine ice sheets, which are grounded below sea level, have been identified as having the potential to contribute significantly to future sea level rise through the rapid loss of ice under changing climate conditions. It has been suggested (Mercer, 1978; Weertman, 1974) that, when they are grounded on a retrograde-sloping bedrock (i.e. sloping downwards towards the interior of the continent), the positive relationship between ice thickness and ice flux leads to a positive feedback in which rapid retreat of the grounding line may occur, termed “marine ice sheet instability” (MISI). More recent analysis has shown that stable grounding line configurations may be possible on retrograde-sloping bedrock when the buttressing of floating ice shelves and 3-D geometry of the system are included (Katz and Worster, 2010; Gudmundsson et al, 2012; Gudmundsson, 2013) or in some configurations

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