Is ice loss from West Antarctica driven by ocean forcing or ice and ocean feedbacks?

南极冰盖是一块比欧洲还大的冰，在某些地方从上到下有几公里。由于内部的降雪，它在自身重量的作用下向外扩散，在边缘以巨大的冰架形式漂浮，面积从大伦敦到法国。然后冰架被来自南大洋的沃茨从下面融化。该系统的输入和输出是如此巨大，即使是非常小的不平衡也会对全球海平面产生灾难性的影响：南极洲的一部分被称为南极西部冰盖（WAIS），由于其下面基岩的形状而被怀疑不稳定，如果它完全崩溃，将导致海平面上升3-5米。卫星观测表明，一些快速-将冰带出南极洲的流出冰川的流动速度急剧加快。松岛冰川是WAIS的重要组成部分，在过去的几十年里，它的速度几乎翻了一番，给冰盖造成了巨大的负失衡。这种加速被认为与该地区观察到的高冰下冰架融化率有关。这种融化降低了松岛冰架阻挡冰川补给的能力。冰架融化速度加快可能是由于海洋变暖;但最近的研究表明，融化实际上也可能强烈依赖于冰架和冰盖的行为。此外，最近的一项冰川学建模研究表明，可能已经越过了一个“临界点”，尽管是由海洋引发的冰退缩，但现在无论融化与否，冰退缩都是自我延续的。确定观测到的后退是由于持续的气候强迫，还是由于耦合的冰-海洋系统的反馈，对于预测在拟议的工作中，我们将通过开发一个复杂的冰盖和海洋相互作用的计算机模型来解决这个问题，并通过受控模拟实验研究冰退缩的过程。冰-海相互作用的理想化实验将导致松岛冰川的现实模拟研究，旨在评估强迫和反馈在其观测到的退缩中的相对重要性。目前，还没有一个数值模型能够完全代表冰盖、冰架和在它们下面循环的海洋之间的密切相互作用。此外，冰和海洋代码，以及理想地适合耦合在一起，共享的属性，将允许深入调查模型的敏感性和控制，并纳入冰盖观测在物理上一致的方式，大大提高了结果的可靠性。

The Antarctic Ice Sheet is a mass of ice larger than Europe, in some places several kilometres from top to bottom. Fed by snowfall over its interior, it spreads out under its own weight, going afloat at its edge in the form of enormous ice shelves with areas ranging from that of Greater London to that of France. The ice shelves are then melted from below by waters from the Southern Ocean. The inputs and outputs of the system are so massive that even very small imbalances can have catastrophic effects on global sea level: the portion of Antarctica known as the West Antarctic Ice Sheet (WAIS), suspected unstable due to the shape of its underlying bedrock, would contribute 3-5 m of sea level rise were it to collapse completely.Satellite observations have shown that some of the fast-flowing outlet glaciers that carry ice out of Antarctica have sped up dramatically. Pine Island Glacier, which drains a significant portion of WAIS, has nearly doubled its speed in the last several decades, creating a large negative imbalance for the ice sheet. The acceleration is thought to be connected to the high under-ice shelf melt rates observed in the region. This melting reduces the ability of the Pine Island Ice Shelf to hold back the glacier feeding it. Increased ice-shelf melt rates are possibly due to warming oceans; but recent studies suggest that melting could actually be strongly dependent on ice shelf and ice sheet behaviour as well. Additionally, a recent glaciological modelling study suggests a "tipping point" may have been crossed, and that ice retreat, though triggered by oceans, is now self-perpetuating regardless of melting. Determining whether the observed retreat is due to ongoing climate forcing, or to feedbacks of the coupled ice-ocean system, is of utmost importance to predicting (and if possible mitigating) future sea level contributions from WAIS.In the proposed work we will address this question through the development of a sophisticated computer model of interacting ice sheet and oceans, and by investigation of the processes involved in ice retreat through controlled modelling experiments. Idealized experiments of ice-ocean interactions will lead up to a realistic modelling study of Pine Island Glacier, designed to assess the relative importance of forcing and feedback in its observed retreat.This study will be unprecedented in terms of the tools developed, the experiments undertaken, and the knowledge gained. Presently no numerical model exists that can fully represent the close interaction between ice sheets, ice shelves, and the ocean circulating beneath them. Furthermore the ice and ocean codes, as well as being ideally suited for coupling together, share properties that will allow for in-depth investigation of model sensitivity and controls, and for the incorporation of ice-sheet observations in a physically consistent manner, vastly improving the reliability of results.