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

在这项提案中，我们正在寻求资金，以便在解决全球海平面预测问题所需的规模上，在模拟南极冰盖内的破裂方面取得飞跃。对未来一个世纪海平面预测的最大不确定性来源是海洋冰崖不稳定。这是南极冰盖一种特殊的破坏模式的名称，在这种模式下，巨大的冰崖因断裂而坍塌，暴露出更高的悬崖，从而导致冰不断加速流失到海洋中。目前，在南极洲海平面贡献预测模型中模拟这一过程所需的物理模型是基于一些出口冰川观测到的悬崖崩塌速率的试探性假设。不能保证这种方法会正确地预测南极洲冰层的消失。需要一种更严格的方法。在这项提议中，我们的目标是使用描述粘弹性材料中破裂的物理过程的方程来模拟冰崖的坍塌。我们已经开发了这一过程的详细模型，它使用相场方法来模拟正在崩解的冰锋的机械破坏。我们也有一个冰流的缓慢粘性成分的模型，它在区域尺度上演变成冰盖。冰盖的实际破坏和海平面的贡献将涉及快速破裂过程和较慢的粘性流动，因此迫切需要将这两种模型的优点结合起来。在这个项目中，我们建议将相场方法耦合到大尺度冰模式中，以保持各自的优势。我们希望，这将为其他冰盖模拟小组开辟一条道路，以便对海平面上升的最坏情况的预测不会像今天那样受到海洋冰崖不稳定带来的巨大不确定性的影响。

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.