The stability of grounding lines on retrograde slopes

G. H. Gudmundsson,J. Krug,L. Favier,G. Durand,O. Gagliardini

doi:10.5194/tc-6-1497-2012

Abstract

Abstract. The stability of marine ice sheets grounded on beds that slope upwards in the overall direction of flow is investigated numerically in two horizontal dimensions. We give examples of stable grounding lines on such retrograde slopes illustrating that marine ice sheets are not unconditionally unstable in two horizontal dimensions. Retrograde bed slopes at the grounding lines of marine ice sheets, such as the West Antarctic Ice Sheet (WAIS), do not per se imply an instability, nor do they imply that these regions are close to a threshold of instability. We therefore question those estimates of the potential near-future contribution of WAIS to global sea level change based solely on the notion that WAIS, resting on a retrograde slope, must be inherently unstable.

Highlights

Large parts of the West Antarctic Ice Sheet (WAIS) rest below sea level on a bedrock sloping downwards towards the ice sheet’s centre
The question of WAIS being potentially subject to a marine ice-sheet instability (MISI) is of utmost importance for any quantitative estimates of future sea level change, because it raises the possibility of WAIS rapidly contributing several meters of sea level change
A number of runs using the parameters listed in Table 1 and the bed geometry defined by Eqs. (1)–(3) were performed and the runs continued until steady state was reached

Summary

Introduction

Large parts of the West Antarctic Ice Sheet (WAIS) rest below sea level on a bedrock sloping downwards towards the ice sheet’s centre. It has been argued that such marine-type ice sheets on retrograde slopes are inherently unstable and susceptible to rapid disintegration The question of WAIS being potentially subject to a marine ice-sheet instability (MISI) is of utmost importance for any quantitative estimates of future sea level change, because it raises the possibility of WAIS rapidly contributing several meters of sea level change. The possibility of a MISI and the conditions under which such an instability could manifest itself have been investigated by a number of authors. To date most analytical and numerical work has focused on analysing the stability regime of MISI in situations where the problem geometry and the flow field varies primarily in along-flow direction. The problem can be treated as a problem in one horizontal dimension (1HD)

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