TC The Cryosphere TC The Cryosphere 1994-0424 Copernicus Publications Göttingen, Germany 10.5194/tc-6-273-2012 Kinematic first-order calving law implies potential for abrupt ice-shelf retreat Levermann A. 1 2 Albrecht T. 1 2 Winkelmann R. 1 2 Martin M. A. 1 2 Haseloff M. 1 3 Joughin I. 4 Earth System Analysis, Potsdam Institute for Climate Impact Research, Potsdam, Germany Institute of Physics, Potsdam University, Potsdam, Germany University of British Columbia, Vancouver, Canada Polar Science Center, APL, University of Washington, Seattle, Washington, USA 13 03 2012 6 2 273 286 Copyright: © 2012 A. Levermann et al. 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://tc.copernicus.org/articles/6/273/2012/tc-6-273-2012.html The full text article is available as a PDF file from https://tc.copernicus.org/articles/6/273/2012/tc-6-273-2012.pdf

Recently observed large-scale disintegration of Antarctic ice shelves has moved their fronts closer towards grounded ice. In response, ice-sheet discharge into the ocean has accelerated, contributing to global sea-level rise and emphasizing the importance of calving-front dynamics. The position of the ice front strongly influences the stress field within the entire sheet-shelf-system and thereby the mass flow across the grounding line. While theories for an advance of the ice-front are readily available, no general rule exists for its retreat, making it difficult to incorporate the retreat in predictive models. Here we extract the first-order large-scale kinematic contribution to calving which is consistent with large-scale observation. We emphasize that the proposed equation does not constitute a comprehensive calving law but represents the first-order kinematic contribution which can and should be complemented by higher order contributions as well as the influence of potentially heterogeneous material properties of the ice. When applied as a calving law, the equation naturally incorporates the stabilizing effect of pinning points and inhibits ice shelf growth outside of embayments. It depends only on local ice properties which are, however, determined by the full topography of the ice shelf. In numerical simulations the parameterization reproduces multiple stable fronts as observed for the Larsen A and B Ice Shelves including abrupt transitions between them which may be caused by localized ice weaknesses. We also find multiple stable states of the Ross Ice Shelf at the gateway of the West Antarctic Ice Sheet with back stresses onto the sheet reduced by up to 90 % compared to the present state.

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