Elevation Change Anomalies in West Antarctica: implications for the subglacial hydrology of ice streams

南极冰盖（AIS）的表面高度变化应该是缓慢的，因为积雪的模式每年或每个世纪都在变化，而且冰盖流向海洋的速率随时间而变化。最近，卫星数据显示，冰盖表面的一小部分，通常直径小于10公里，经历了非常迅速的海拔变化，最高可达6米，速度超过2厘米/天。这些高程变化异常（ECAs）有时呈簇状出现，部分地表下沉，而冰盖上的其他区域呈下降梯度，显示地表上升。研究人员提出，这些与eca相关的冰盖表面高度的快速变化可能代表了AIS底部的水袋（冰下湖）的填充或排水。这些水袋被认为是AIS底部冰川与沉积物和基岩之间更广泛的湖泊、河流和浅沼泽网络的一部分。如果eca是冰盖底部小袋水的储存和周期性排水的表面表达，它们可能代表了对冰盖流动的重要控制。为了模拟AIS，以及气候变化带来的任何可能的未来流量变化，我们必须了解AIS当前的基础环境。这个项目将帮助科学家了解是什么产生了这些eca。冰盖底部的地形将由探冰雷达确定。如果eca代表的是水袋，那么就会有大面积平坦、明亮的雷达回波。为了证明在任何明亮的反射体下面都有相当厚（分米到米）的水，将使用地震调查来告诉我们在eca下面的冰和下面的沉积物之间是否有水。雷达和地震调查将在2008年和2009年进行，允许在两次调查之间绘制系统的变化。如果没有确定相当大的水深，雷达和地震工作应该提供对产生eca的基础环境的见解，最有可能反映冰流下沉积地貌的快速变化。该项目将与Tulaczyk博士（加州大学）和Joughin博士（华盛顿大学）合作进行。他们计划在2007年、2008年和2009年对宾夏德勒冰盖的eca进行实地考察。这项野外工作将包括在eca上空建立10个长期全球定位系统（GPS），记录2007-2009年的海拔变化。还将进行实地GPS调查。这些实地数据将与卫星数据一起用于调查eca的变化，并改进eca区域的冰流模型。图拉奇克博士和乔金博士最近向美国国家科学基金会（NSF）提交了一份支持GPS和卫星工作的提案，包括三个野外季节的后勤支持。该项目的后勤支持将通过NSF提案得到支持。该NERC提案要求资助主要研究者前往新西兰克赖斯特彻奇参加2008年和2009年的美国实地派对。因此，这笔小额赠款代表了NERC科学的不可思议的价值，因为实地工作预算的核心将通过国际合作得到支持。这是一个小而分散的项目。雷达和地震调查都将是探索性的，因为现场后勤的时间限制，每个现场季节收集的雷达数据不超过5天，地震数据不超过6天。如果成功，该项目将为未来更广泛的雷达和地震调查提供概念验证，这些调查包括Binschadler冰流、南极洲西部的其他简单海岸冰盖系统和南极洲东部的Dome C地区的ECAs基础环境。

The surface elevation of the Antarctic Ice Sheet (AIS) should change only slowly, as patterns of snow accumulation vary from year to year, or century to century, and as the rate of flow of the ice sheet towards the sea changes through time. Recently, satellite data has shown that small parts of the ice sheet surface, often less than 10 km across, have experienced very rapid elevation change, of up to 6m, at rates of over 2 cm/day. These elevation change anomalies (ECAs) are sometimes found in clusters, with some parts of the surface sinking, while other areas down-gradient on the ice sheet, show the surface rising. Researchers have suggested that these rapid changes of ice sheet surface elevation associated with these ECAs may represent the filling or draining of water pockets (subglacial lakes) at the bottom of the AIS. These water pockets are believed to be part of a wider network of lakes, rivers and shallow swamps between the glacier ice at the bottom of the AIS and the sediments and bedrock beneath. If ECAs are the surface expression of the storage and periodic drainage of pockets of water at the bottom of the ice sheet, they may represent an important control on ice sheet flow. In order to model the AIS, and any possible future change in flow brought about by climate change, we must understand the current basal environment of the AIS. This project will help scientists understand what generates these ECAs. The topography at the bottom of the ice sheet will be determined from ice-penetrating radar. If ECAs represent water pockets, extensive areas of flat, bright radar returns would be expected. In order to prove that there is considerable (decimetre to metre) thickness of water beneath any bright reflectors, seismic surveys will be used to tell us if there is water between the ice and underlying sediment beneath the ECAs. Radar and seismic surveys will be undertaken in 2008 and 2009, allowing change in the system to be mapped between the two surveys. If considerable water depths are not identified, the radar and seismic work should provide insights into the basal environment responsible for the generation of ECAs, most likely reflecting rapid changes in sedimentary landforms beneath the ice stream. The project will be conducted in collaboration with Dr. Tulaczyk (University of California) and Dr. Joughin (University of Washington). They plan to carry out fieldwork over the ECAs on the Binschadler Ice Sheet during 2007, 2008 and 2009. This fieldwork will involve setting up 10 long-term global positioning systems (GPS) over the ECAs, recording elevation change from 2007-2009. Field GPS surveys will also be conducted. This field data will be used along with satellite data to investigate change in ECAs and to improve models of ice flow in the region of the ECAs. Dr. Tulaczyk and Dr. Joughin have recently submitted a National Science Foundation (NSF) proposal to support the GPS and satellite work, including logistic support for three field seasons. Logistic support for this project will be supported through the NSF proposal. This NERC proposal asks for funding to allow the Principle Investigator to travel to Christchurch, New Zealand to join the US field party in 2008 and 2009. As such, this small grant represents incredible value for money for NERC science, as the core of the fieldwork budget will be supported through the international collaboration. This is a small, discrete project. Both radar and seismic surveys will be exploratory, as time constraints on field logistics will allow no more than 5 days of radar data and 6 days of seismic data to be collected during each field season. If successful, this project will provide proof-of-concept for future, more extensive radar and seismic investigations of the basal environment of ECAs on the Binschadler Ice Stream, other Siple Coast Ice Sheet systems in West Antarctica and the Dome C area of East Antarctica.