Parameterization of basal friction near grounding lines in a one-dimensional ice sheet model

G. R. Leguy,X. S. Asay-Davis,W. H. Lipscomb

doi:10.5194/tc-8-1239-2014

Abstract

Abstract. Ice sheets and ice shelves are linked by the transition zone, the region where flow dominated by vertical shear stress makes a transition to flow dominated by extensional stress. Adequate resolution of the transition zone is necessary for numerically accurate ice sheet–ice shelf simulations. The required resolution depends on how the basal physics is parameterized. We propose a~new, simple parameterization of the effective pressure near the grounding line, combined with an existing friction law linking effective pressure to basal stress and sliding, in a one-dimensional, fixed-grid, vertically integrated model. This parameterization represents connectivity between the basal hydrological system and the ocean in the transition zone. Our model produces a smooth transition between finite basal friction in the ice sheet and zero basal friction in the ice shelf. In a set of experiments based on the Marine Ice Sheet Model Intercomparison Project (MISMIP), we show that with a smoother basal shear stress, the model yields accurate steady-state results at a fixed-grid resolution of ~1 km.

Highlights

Antarctica’s contribution to sea level rise has increased in the past decade
In a set of experiments based on the Marine Ice Sheet Model Intercomparison Project (MISMIP), we show that with a smoother basal shear stress, the model yields accurate steady-state results at a fixed-grid resolution of ∼ 1 km
The results described are based on the MISMIP experiments (Pattyn et al, 2012), which are designed to study the transient behavior of marine ice-sheet models

Summary

Introduction

Antarctica’s contribution to sea level rise has increased in the past decade. While the contribution of the East Antarctic Ice Sheet (EAIS) remains steady, mass loss from the West Antarctic Ice Sheet (WAIS) has more than doubled (Velicogna, 2009; Rignot et al, 2011). Theoretical models suggest that marine ice sheets like WAIS are susceptible to instabilities when they lie on bedrock that slopes upward in the direction of ice flow (Weertman, 1974; Schoof, 2007a) If these instabilities are triggered, mass loss will accelerate, exacerbating future sea-level rise and potentially leading to WAIS collapse (Vaughan and Spouge, 2002; Joughin and Alley, 2011). For this reason it is important to understand the dynamic processes that drive ice sheets in the region. Even the more accurate flow approximations require very fine resolution (< 1 km) in the transition zone

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Discussion

Conclusion