Evolution of a coupled marine ice sheet–sea level model

Natalya Gomez,Jerry X Mitrovica,David Pollard,Peter U Clark,Peter Huybers

doi:10.1029/2011jf002128

Abstract

We investigate the stability of marine ice sheets by coupling a gravitationally self‐consistent sea level model valid for a self‐gravitating, viscoelastically deforming Earth to a 1‐D marine ice sheet‐shelf model. The evolution of the coupled model is explored for a suite of simulations in which we vary the bed slope and the forcing that initiates retreat. We find that the sea level fall at the grounding line associated with a retreating ice sheet acts to slow the retreat; in simulations with shallow reversed bed slopes and/or small external forcing, the drop in sea level can be sufficient to halt the retreat. The rate of sea level change at the grounding line has an elastic component due to ongoing changes in ice sheet geometry, and a viscous component due to past ice and ocean load changes. When the ice sheet model is forced from steady state, on short timescales (<∼500 years), viscous effects may be ignored and grounding‐line migration at a given time will depend on the local bedrock topography and on contemporaneous sea level changes driven by ongoing ice sheet mass flux. On longer timescales, an accurate assessment of the present stability of a marine ice sheet requires knowledge of its past evolution.

Highlights

[1] We investigate the stability of marine ice sheets by coupling a gravitationally self-consistent sea level model valid for a self-gravitating, viscoelastically deforming Earth to a 1-D marine ice sheet-shelf model
The ice shelves that fringe the West Antarctic Ice Sheet (WAIS) are known to have a stabilizing or buttressing effect on the ice sheet [Thomas and Bentley, 1978; Dupont and Alley, 2005; Goldberg et al, 2009], but these shelves appear susceptible to climate change since warming of the atmosphere and/or ocean could lead to increased melting and disintegration either from above and/or below, respectively [Jenkins and Doake, 1991; Rignot and Jacobs, 2002; MacAyeal et al, 2003]
Gomez et al [2010b] coupled predictions of this instantaneous sea level fingerprint to the Weertman [1974] steady state 1-D ice sheet model, and they demonstrated that on a reversed bed, the sea level fall resulting from ice loss compensates for the deepening of the bed, and for some reversed bed slopes this compensation is sufficient to stabilize the ice sheet

Summary

Introduction

[2] The stability of polar ice sheets, and in particular that of the West Antarctic Ice Sheet (WAIS), is of central concern within studies of modern climate change [Lenton et al, 2008; Smith et al, 2009]. Large-scale changes in ice sheets can take place over several thousand years or longer, and on these timescales, the viscous response of the upper mantle and crust, which will be a function of the entire pre-history of ice and ocean loading, can contribute significantly to local changes in sea level In this case, the elastic and viscous responses combine to produce, for example, a localized zone of crustal uplift in the vicinity of a melting ice sheet and a subsidence of surrounding forebulges as the system relaxes toward isostatic equilibrium. The elastic and viscous responses combine to produce, for example, a localized zone of crustal uplift in the vicinity of a melting ice sheet and a subsidence of surrounding forebulges as the system relaxes toward isostatic equilibrium To model such effects, we adopt a gravitationally self-consistent sea level model that accounts for the deformation of a self-gravitating, viscoelastic Earth model [Kendall et al, 2005; Gomez et al, 2010a]. We employ a dynamic ice sheet model [Pollard and DeConto, 2007, 2009] to investigate how sea level changes influence the timescale and extent of retreat of a marine ice sheet subject to a perturbation in climate

Model Setup

Ice Sheet

Experiments

Findings

Conclusions