iSTAR C: Dynamical control on the response of Pine Island Glacier

预计海平面上升将在未来几十年到几个世纪内影响世界各地的沿海社区。在英国，沿海社区和资产的脆弱性最能体现在海防超限的可能性上。例如，当它们建成时，伦敦市的海上防御工事(包括泰晤士河屏障)旨在保护伦敦免受除千年一遇的洪水之外的所有洪水的伤害。全球海平面上升50厘米将使这一保护水平减少到1-100年，而上升100厘米将减少到10年一次。松岛冰川是南极洲西部的五个冰川之一，它们目前正在显著且加速地推动海平面上升。目前受变薄影响的部分含有足够的冰，足以使全球海平面上升约25厘米--其邻国的冰层又增加了50厘米。鉴于冰层融化的速度及其对海防规划的潜在影响，显然需要了解和预测松岛冰川及其邻近地区的未来。然而，正如政府间气候变化专门委员会(IPCC，2007)所强调的那样，人们对动态变化通过排干冰盖的冰川传递的方式了解得如此之少，以至于IPCC认为这是下个世纪对海平面上升的最少了解，但可能是最大的贡献。ISTAR-C将通过寻求了解负责传递漂浮冰架变薄影响的过程，直接解决这种知识的缺乏，ISTAR-C还将使用现有的最新方法来测量松岛冰川几个位置下面的床的性质(岩石类型和水分含量)，以确定它们对变薄传播的影响。我们将检验这一假设，即正是这些河床条件导致了松岛冰川支流似乎以不同的速度变薄的事实。检验这一假说将使我们更好地理解如何预测未来冰川变薄的速度。为了实现这些目标，我们将在两个野外季节收集松岛冰川的数据。这些将包括精确测量从冰架向上冰川进入其支流的冰流的变化。我们将使用雷达和地震技术对冰川床进行成像，并使用卫星遥感来测量地面无法进入的地区冰川不断变化的形状。我们将使用我们收集的数据来驱动和验证一组松岛冰川动力学的计算机模拟。每一项都将测试冰川流动的一个特定方面，并允许我们用真实数据来测试我们目前的知识和假设。这项工作产生的模型将明显更可靠地模拟冰川过去的变化，从而减少了预测这种变化的未来演变以及由此导致的海平面上升的不确定性。总体而言，这一计划将显著提高对冰川与其河床相互作用的理解，并提供关于地球上变化最快、最重要的冰川之一--松岛冰川的非常具体的教训。

It is expected that sea-level rise will impact coastal communities worldwide over the coming decades to centuries. In the UK, the vulnerability of coastal communities and assets is best characterised in terms of the likely frequency of the over-topping of sea-defences. For example, when they were built, the sea-defences for the city of London (including the Thames Barrier) were designed to protect London from all except the 1-in-1000 year flood event. A rise of 50 cm in global sea level will reduce this level of protection to 1-100 years, and a rise of 100 cm would reduce it to 1-in-10 years. Pine Island Glacier is one of five glaciers in West Antarctica that are currently contributing sea-level rise at a significant and accelerating rate. The portion currently affected by thinning contains sufficient ice to raise global sea-level by around 25 cm - its neighbours account for another 50 cm. Given the rate of ice-loss and the potential implications for sea-defence planning there is a clear requirement to understand and predict the future of Pine Island Glacier and its neighbours. However, as highlighted by the Intergovernmental Panel on Climate Change (IPCC, 2007), understanding the way that dynamic changes are transmitted through the glaciers draining ice sheets is so poorly understood that the IPCC believed it was the least well understood, and potentially the largest, contribution to sea-level rise in the coming century.ISTAR-C will directly address this lack of knowledge, by seeking to understand the processes that are responsible for transmitting the effect of thinning of the floating ice shelf, upstream such that thinning can now be seen on much of the trunk and tributaries of Pine Island Glacier.ISTAR-C will also use the most up-to-date methods available to measure the properties (rock-type and water-content) of the bed beneath several locations on Pine Island Glacier to determine their influence on the propagation of thinning. We will test the hypothesis that it is these bed conditions that are responsible for the fact that the tributaries of Pine Island Glacier appear to be thinning at different rates. Testing this hypothesis will give us a much better understanding on which to predict the future magnitudes of ice-thinning rates for the glacier. To achieve these objectives we will collect data from Pine Island Glacier during two field seasons. These will include precise measurement of variations in ice-flow from the ice-shelf up the glacier and into its tributaries. We will image the bed of the glacier using radar and seismic techniques, and use satellite remote sensing to measure the changing configuration of the glacier in areas that cannot be accessed on the ground. We will use the data we have collected to drive and verify a set of computer simulations of the dynamics of Pine Island Glacier. Each of these will test a particular aspect of the glacier flow, and allow us to test our current knowledge and hypotheses against real data. The models that emerge from the exercise will be demonstrably more reliable in simulating past changes on the glacier, and thus have reduced uncertainty in predicting the future evolution of such changes, and the consequential contribution to sea-level rise.Overall, this programme will deliver significant improvements in understanding of how glaciers in general interact with their beds, and very specific lessons about one of the most rapidly-changing and significant glaciers on the planet, Pine Island Glacier.