Processes of fast glacier flow

冰盖和冰川是未来海平面上升的最大潜在来源。山脉冰川在区域供水中也发挥着重要作用，特别是通过在干旱的夏季供水，而格陵兰和南极洲等大陆大小的冰盖对世界气候系统的影响超出海平面变化。冰流是决定地球上有多少冰的关键因素：更快的冰流往往会导致更薄、更小的冰块，甚至可能导致冰川或冰盖完全消失。然而，关于地球上最快的冰川流动现象是如何工作的，人们知之甚少--南极洲的冰流，汹涌的冰川，以及流入海洋的快速流动的冰川。这项拟议的研究旨在揭开这些现象背后的物理学原理。它将重点放在融化的水在加快冰流方面所起的作用。大多数快速的冰川流动是由于到达冰床的融化水对冰底的润滑造成的。然而，要量化水的影响，光知道有多少水到达床上是不够的：我们还必须知道水是如何沿着床排出的。高压水会削弱冰和岩石之间的接触，从而允许更快的滑动。我的研究将使用数学建模技术，结合对山谷冰川床的直接观察，确定控制冰下水压的物理因素，并将该物理因素引入冰流模拟，以更好地预测其对快速冰流现象的影响。除了对水的关注外，我还将开发新的建模技术来捕捉冰山的破裂，以及通过消除对冰流的限制来减缓冰流入海洋的影响。我之所以做出这一努力，是因为格陵兰岛和南极洲质量下降最快的部分总是以海洋为终点的出口冰川，在那里，失去漂浮的冰舌(或“冰架”)消除了对冰流的限制。未来对冰排放的预测将关键取决于能否理解漂浮的冰舌是如何以及为什么断裂的，我的工作将致力于为潜在的物理产生预测模型。

Ice sheets and glaciers are the biggest potential source of future sea level rise. Mountain glaciers also play an important role in regional water supplies, especially through providing water during dry summers, while continent-sized ice sheets such as those in Greenland and Antarctica have multple impacts on the world's climate system beyond sea level change. Ice flow is a key component in determining how much ice there is on the planet: faster ice flow tends to lead to thinner, smaller ice masses, and potentially even to the complete disappearance of a glacier or ice sheet. Yet relatively little is known about how the fastest glacial flow phenomena on Earth work - ice streams in Antarctica, surging glaciers, and fast-flowing glaciers that teminate in the ocean. The proposed research aims to unravel the physics behind these phenomena. It will focus on the role that melt water plays in speeding up ice flow. Most fast glacier flow is caused by lubrication of the base of the ice by melt water that reaches the bed. To quantify the effect of water, it is however not enough to know how much of it reaches the bed: we also have to know how it drains along the bed. Highly pressurized water will weaken the contact between ice and rock, and permit faster sliding. My research will use mathematical modelling techniques in combination with direct observations at the bed of a valley glacier to determine the physics that controls water pressure under the ice, and to introduce that physics into ice flow simulations to better predict its effects on fast ice flow phenomena. Alongside this focus on water, I will develop novel modelling techniques to capture the breaking-off of icebergs, and the effect that this has through removing constrictions on ice flow that slow ice discharge into the oceans. I am motivated in this effort by the fact that the parts of Greenland and Antarctica that are losing mass fastest are invariably outlet glaciers that terminate in the ocean, where the loss of a floating ice tongue (or `ice shelf') has removed a constriction to ice flow. Future projections of ice discharge will crucially depend on being to understand how and why floating ice tongues break off, and my work will aim to produce predictive models for the underlying physics.