Abstract
Abstract. Using a numerical ice flow model, we study changes in ice shelf buttressing and grounding-line flux due to localized ice thickness perturbations, a proxy for localized changes in sub-ice-shelf melting. From our experiments, applied to idealized (MISMIP+) and realistic (Larsen C) ice shelf domains, we identify a correlation between a locally derived buttressing number on the ice shelf, based on the first principal stress, and changes in the integrated grounding-line flux. The origin of this correlation, however, remains elusive from the perspective of a theoretical or physically based understanding. This and the fact that the correlation is generally much poorer when applied to realistic ice shelf domains motivate us to seek an alternative approach for predicting changes in grounding-line flux. We therefore propose an adjoint-based method for calculating the sensitivity of the integrated grounding-line flux to local changes in ice shelf geometry. We show that the adjoint-based sensitivity is identical to that deduced from pointwise, diagnostic model perturbation experiments. Based on its much wider applicability and the significant computational savings, we propose that the adjoint-based method is ideally suited for assessing grounding-line flux sensitivity to changes in sub-ice-shelf melting.
Highlights
Marine ice sheets like that overlying West Antarctica are grounded below sea level, and their bedrock would remain so even after full isostatic rebound (Bamber et al, 2009)
We perturb the coupled ice sheet–shelf system by decreasing the ice thickness uniformly by 1 m at ice shelf grid cells, after which we examine the instantaneous impact on kinematics and dynamics
A decrease in ice shelf buttressing tends to lead to an increase in grounding-line flux (GLF) (e.g., Gagliardini et al, 2010; see Fig. 2a) and intuitively we expect that the GLF should be relatively more sensitive to ice shelf thinning in regions of relatively larger buttressing
Summary
Marine ice sheets like that overlying West Antarctica (and to a lesser extent portions of East Antarctica) are grounded below sea level, and their bedrock would remain so even after full isostatic rebound (Bamber et al, 2009) This and the fact that ice sheets generally thicken inland lead to a geometric configuration prone to instability; a small increase in flux at the grounding line thins the ice there, leading to floatation, a retreat of the grounding line into deeper water, further increases in flux (due to still thicker ice), and further thinning and grounding-line retreat. Three-dimensional ice shelves, buttressing results from three main sources: (1) along-flow
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