A23. Sensitivity of grounding line flux

Diagnosing the sensitivity of grounding line flux to changes in sub-ice shelf melting

Title

Diagnosing the sensitivity of grounding line flux to changes in sub-ice shelf melting

Authors

Tong Zhang (Unlicensed), Stephen Price, Matt Hoffman, Mauro Perego, Xylar Asay-Davis

Abstract

We seek to understand causal connections between changes in sub-ice shelf melting, ice shelf buttressing, and grounding line flux. We study changes in ice shelf buttressing and grounding line flux as a function of localized ice thickness perturbations -- a proxy for changes in sub-ice shelf melting -- applied to both idealized (MISMIP+) and realistic (Larsen C) model domains. From this, we identify a strongly direction-dependent ``buttressing number'' that links local changes in ice shelf thickness and ice dynamics to changes in the integrated grounding line flux. We find that a buttressing number calculated along the first principal stress direction or the ice flow direction correlates better with changes in grounding line flux than one calculated along the second principal stress direction. We also present an adjoint-based method for calculating the sensitivity of the integrated grounding line flux to local changes in ice shelf geometry. The adjoint-based sensitivity is nearly identical to that deduced from pointwise, forward model perturbation experiments except very near to the grounding line where the dependence of ice flux on the ice thickness is highly nonlinear. Because of the significant computational savings afforded by the adjoint-based sensitivity calculation and because it is accurate over the majority of the ice shelf, we propose that it is ideally suited for assessing grounding line flux sensitivity to changes in sub-ice shelf melting.