Fracture: At the frontier of Antarctica's contribution to sea level

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In this proposal we are seeking funding to make a leap towards simulating fracture within the Antarctic Ice Sheet on the scales that will be needed to address the problem of predicting global sea level. The largest source of uncertainty in projections of sea level over the coming century is due to the Marine Ice Cliff Instability. This is the name given to a particular mode of failure of the Antarctic ice sheet in which large ice cliffs collapse due to fracture, exposing even taller cliffs, thus leading to an ever accelerating loss of ice to the ocean. The physical models needed to simulate this process in predictive models of the sea level contribution from Antarctica are presently based upon heuristic assumptions that use cliff collapse rates observed in a few outlet glaciers. There is no guarantee that this approach will correctly predict the loss of ice from Antarctica. A more rigorous approach is needed. In this proposal we aim to simulate the collapse of ice cliffs using equations that describe the physical process of fracture in a viscoelastic material. We have already developed a detailed model of this process that uses a phase-field approach to simulate the mechanical failure of a calving ice front. We also have a model of the slow viscous component of the ice flow that evolves the ice sheet on a regional scale. The actual failure of the ice sheet and the sea level contribution will involve both the rapid fracture processes and the slower viscous flow, so there is an urgent need to combine the strengths of both models. In this project, we propose to couple the phase-field approach within the broad-scale ice model in a way that preserves the advantage of each. We hope that this will establish a path for other ice sheet modelling groups to follow so that projections of the worst case for sea level rise are not subject to the enormous uncertainty from the Marine Ice Cliff Instability that they are today.