Hydrostatic grounding line parameterization in ice sheet models

H Seroussi,E Rignot,A Khazendar,E Larour,M Morlighem

doi:10.5194/tc-8-2075-2014

H Seroussi, E Rignot + Show 3 more

Open Access

https://doi.org/10.5194/tc-8-2075-2014

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Abstract

Abstract. Modeling of grounding line migration is essential to accurately simulate the behavior of marine ice sheets and investigate their stability. Here, we assess the sensitivity of numerical models to the parameterization of the grounding line position. We run the MISMIP3D benchmark experiments using the Ice Sheet System Model (ISSM) and a two-dimensional shelfy-stream approximation (SSA) model with different mesh resolutions and different sub-element parameterizations of grounding line position. Results show that different grounding line parameterizations lead to different steady state grounding line positions as well as different retreat/advance rates. Our simulations explain why some vertically depth-averaged model simulations deviate significantly from the vast majority of simulations based on SSA in the MISMIP3D benchmark. The results reveal that differences between simulations performed with and without sub-element parameterization are as large as those performed with different approximations of the stress balance equations in this configuration. They also demonstrate that the reversibility test is passed at relatively coarse resolution while much finer resolutions are needed to accurately capture the steady-state grounding line position. We conclude that fixed grid SSA models that do not employ such a parameterization should be avoided, as they do not provide accurate estimates of grounding line dynamics, even at high spatial resolution. For models that include sub-element grounding line parameterization, in the MISMIP3D configuration, a mesh resolution finer than 2 km should be employed.

Highlights

Mapping of grounding lines, where ice detaches from the underlying bedrock and becomes afloat in the ocean, is possible using satellite remote sensing with either visible imagery (Bohlander and Scambos, 2007) or differential radar interferometry (Goldstein et al, 1993; Rignot et al, 2011b)
We investigate the influence of grounding line parameterization on grounding line steady state position as well as its dynamic response to a perturbation in basal friction in the grounding line area
We show that mesh refinement and grounding line parameterization both have a significant influence on modeled grounding line positions, as well as advance and retreat rates

Summary

Introduction

Mapping of grounding lines, where ice detaches from the underlying bedrock and becomes afloat in the ocean, is possible using satellite remote sensing with either visible imagery (Bohlander and Scambos, 2007) or differential radar interferometry (Goldstein et al, 1993; Rignot et al, 2011b). Observations show that grounding lines have a dynamic behavior. This is the case in the Amundsen Sea sector of West Antarctica, where their migration inland reaches more than 1 km yr−1 on Pine Island and Thwaites Glacier (Rignot et al, 2011a). Accurate knowledge of grounding line positions as well as their evolution in time is critical to understand ice sheet dynamics. Grounding line dynamics are strongly non-linear, with long episodes of relative stability interrupted by significant retreat, this evolution being controlled, among other factors, by basal topography (Weertman, 1974; Durand et al, 2009b). The Antarctic ice sheet is surrounded by floating ice shelves of varying size, and modeling of this transition zone is essential to simulate the evolution of polar ice sheets in our changing climate

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