Basal Conditions on Rutford Ice Stream: Bed Access, Monitoring and Ice Sheet History

南极和格陵兰冰盖在控制地球海平面和气候方面发挥着重要作用，但我们对它们的历史和运动的了解很少。目前，我们预测未来海平面的能力最大的不确定性来自于这些冰盖。这一点尤其重要，因为冰盖造成的海平面上升速度比预期的要快，而且冰盖有可能引发不可逆转的海平面上升，这种上升将持续许多世纪。减少这种不确定性是目前冰川学面临的最大挑战之一。我们的项目旨在提高我们对这种不确定性的两个方面的理解：第一，南极西部冰盖（WAIS）过去的行为，第二，快速冰流的流动。通过选择合适的位置，我们可以在一个项目中实现这两个目标。拉特福德冰流是大型快速流动的冰川之一，它将WAIS排出并将冰输送到海洋中。它的优点是已经从地面野外工作、飞机和卫星上收集了大量数据。下一步是直接进入冰河床，现有的数据意味着我们可以确定最佳的位置。使用热水钻，我们将在冰流的床上打洞，穿过2公里多厚的冰。一旦钻头到达地层，我们将从冰下收集沉积物样本。我们还将从冰柱上收集冰芯的部分。一连串的仪器将被放入洞中，以测量冰下水系统的压力、冰的温度分布以及冰向下游流动时的变形方式。我们还将在床上插入探针，以测量冰滑动的速度，以及床上沉积物的强度。钻孔摄像机将记录冰、床和水系统的性质，包括有多少沉积物被冻结在冰的底部。在冰流表面，我们将进行一些地球物理实验，旨在研究冰的流动，并绘制地形图以及钻孔周围地区的基础水和沉积物的变化。这将有助于我们解释在钻孔中进行的测量。GPS接收器将跟踪冰面的运动；地震勘测将绘制出较软和较硬的地层沉积物区域；雷达勘测将显示冰川下的水集中或分布在哪里；地震仪阵列将探测到冰流在床上碾压时发出的噪音。项目结果将在英国南极调查局、斯旺西大学和NERC-GEF进行分析。NASA-JPL、伦敦大学学院和布里斯托尔大学的其他项目合作伙伴也将做出贡献。完成后，该项目将提供以下信息：-该地区冰盖最近崩塌的年龄-冰下的水系统-冰和床的热状态-冰运动在三种不同流动机制之间的划分-滑动，冰变形和床变形最后一次冰盖崩塌的时间将非常有价值，因为在该地区还没有其他信息存在。它将帮助我们了解过去随着气候变暖和变冷，冰盖是如何变化的。我们的其他结果——表征冰流动力学以及冰、水和沉积层如何相互作用——将帮助我们理解冰流运动的过程，以及我们应该如何将这些过程纳入模型。这些结果将有助于澄清以前在南极洲其他地方的冰流中所做的工作，这些工作在某些情况下是相互矛盾或不确定的。总的来说，这些结果将使我们在了解冰盖过去的行为方式，今天控制它们的因素以及它们未来如何演变的能力方面向前迈出一大步。

The Antarctic and Greenland ice sheets play a major role in controlling Earth's sea level and climate, but our understanding of their history and motion is poor. At the moment, the biggest uncertainty in our ability to predict future sea level comes from these ice sheets. This is particularly important because sea level rise from ice sheets is increasing faster than expected, and because ice sheets have the potential to trigger irreversible sea level rise that would continue for many centuries. Reducing this uncertainty is currently one of the biggest challenges in glaciology. Our project aims to improve our understanding of two aspects of this uncertainty: first, the past behaviour of the West Antarctic Ice Sheet (WAIS), and second, the flow of the fast ice streams that drain it. By choosing the right location, we can address both these aims within one project. Rutford Ice Stream is one of the large, fast-flowing glaciers that drain WAIS and deliver the ice to the ocean. It has the advantage that a large amount of data have already been collected there from surface fieldwork, from aircraft, and from satellites. The next step is to access the ice stream bed directly, and the existing data mean we can identify the optimum locations for this. Using a hot-water drill we will make holes to the bed of the ice stream, through ice more than 2 km thick. Once the drill reaches the bed we will collect samples of sediment from beneath the ice. We will also collect sections of ice core from the ice column. Strings of instruments will be lowered down the holes to measure the pressure in the water system beneath the ice, the temperature profile in the ice and the way the ice deforms as it flows downstream. We will also insert probes into the bed that will measure how fast the ice is sliding, as well as the strength of the sediment in the bed itself. Borehole video cameras will record the nature of the ice, bed and water system, including how much sediment is frozen into the bottom of the ice. On the ice stream surface we will carry out a number of geophysical experiments designed to study the flow of the ice and to map the topography and the variations in basal water and sediment in the area around the drill holes. This will help us to interpret the measurements made in the drill holes. GPS receivers will track the motion of the ice surface; seismic surveys will map the softer and harder areas of bed sediment; radar surveys will show where water beneath the glacier is concentrated or distributed; and a seismometer array will detect the noise bursts emitted as the ice stream grinds over its bed. Project results will be analysed at the British Antarctic Survey, Swansea University and NERC-GEF. Other project partners at NASA-JPL, University College London and the University of Bristol will also contribute. When completed, the project will give information on: - An age for the most recent collapse of the ice sheet in this region - The water system beneath the ice - The thermal regime of the ice and bed - The partition of ice motion between the three different flow mechanisms - sliding, ice deformation and bed deformation The timing of the last ice sheet collapse will be extremely valuable because no other information yet exists in this region. It will help us to understand the way the ice sheet has changed as climate has warmed and cooled in the past. Our other results - characterising ice stream dynamics and how ice, water and the sedimentary bed interact - will help us understand the processes by which ice streams move, and how we should include these processes into models. The results will help to clarify previous work from ice streams elsewhere in Antarctica, which in some cases have been contradictory or inconclusive. Overall, these results will be big steps forward in our ability to understand the way ice sheets behaved in the past, what controls them today, and how they might evolve in the future.