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

南极冰盖（AIS）的表面高度应该只会缓慢变化，因为积雪的模式每年或世纪与世纪不同，冰盖流向海洋的速度也会随着时间而变化。最近，卫星数据显示，冰盖表面的一小部分，通常不到10公里宽，经历了非常迅速的海拔变化，高达6米，速度超过2厘米/天。这些高程变化异常（ECAs）有时是成簇出现的，某些部分的地表下沉，而冰盖上的其他梯度下降的区域则显示地表上升。研究人员认为，与这些ECA相关的冰盖表面高程的快速变化可能代表了AIS底部水囊（冰下湖泊）的填充或排水。这些水囊被认为是AIS底部冰川冰与其下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是冰盖底部水囊的储存和定期排水的表面表达，它们可能代表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。该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冰层穿透雷达确定。如果ECA代表水囊，那么预计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层下面都有相当厚的水（分米到米），将使用地震勘测来告诉我们在ECA下面的冰和底层沉积物之间是否有水。2008年和2009年将进行雷达和地震勘测，以便在两次勘测之间对系统的变化进行测绘。如果没有确定相当大的水深，雷达和地震工作应该提供对负责生成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年对宾沙德勒冰盖的ECA进行实地考察。这项实地工作将涉及在出口管制区设置10个长期全球定位系统，记录2007-2009年的海拔变化。还将进行实地全球定位系统调查。这一实地数据将与卫星数据一起沿着用于调查南极冰区的变化，并改进南极冰区区域的冰流模型。Tulaczyk博士和Joughin博士最近提交了一份国家科学基金会（NSF）的建议，以支持GPS和卫星工作，包括三个实地季节的后勤支持。该项目的后勤支持将通过NSF提案得到支持。该NERC提案要求提供资金，以允许主要研究者前往新西兰的基督城，参加2008年和2009年的美国实地考察。因此，这笔小额赠款对NERC科学来说是难以置信的物有所值，因为实地工作预算的核心将通过国际合作得到支持。这是一个小型的、独立的项目。雷达和地震勘测都将是探索性的，因为实地后勤的时间限制将允许在每个实地季节收集不超过5天的雷达数据和6天的地震数据。如果成功，该项目将为今后对宾沙德勒冰流、南极洲西部其他西普尔海岸冰盖系统和南极洲东部圆顶C地区的ECA基础环境进行更广泛的雷达和地震调查提供概念验证。

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.