Subglacial Lakes and the Onset of Ice Streaming: Recovery Lakes

贝尔/0636883该奖项支持一个研究冰下水在主要冰盖整体稳定性中所起作用的项目。据估计，目前南极洲的冰下湖泊中储存着22 000立方公里的水。这些水的运动是通过南极洲东部和西部的一个复杂的、在很大程度上是推断出来的排水系统进行的。冰下湖泊灾难性排水的地貌证据记录了重复的事件。这些主要的洪水事件似乎已经排干了位于相对稳定的东南极冰盖内部的最大的冰下湖泊。新出现的证据表明，重要的冰下湖泊与东南极洲最大的冰流之一恢复冰流的出现之间存在密切联系。 我们对南极洲东部恢复湖地区的初步分析表明，湖泊和冰流之间存在直接联系，特别是800公里长的恢复冰流及其支流。恢复湖区（Recovery Lakes Region）位于恢复冰流（Recovery Ice Stream）的上坡处，由3个轮廓分明的湖泊和第四个模糊的“湖泊状”特征组成。虽然其他大型湖泊对冰面坡度有局部影响，但恢复湖区湖泊与冰盖表面坡度的突然区域变化一致。卫星图像显示，该湖区的下坡边缘包含明显的流动带和裂缝：两者都表明冰的速度在增加。在南极洲东部发现一系列大型湖泊，同时出现快速的冰流，首次将冰下湖泊和冰盖动态明确联系起来。将恢复排水冰流的开始与一系列大型冰下湖泊联系起来的证据提出了一个根本问题：冰下湖泊如何触发冰流的开始？我们提出了两种可能的机制：（i）冰下湖泊可以通过湖泊冰盖下斜坡的湖水排放产生加速的冰流。(ii)冰下湖泊可以产生加速的冰流，加速的冰流是通过湖泊上方的基底增积来改变基底的温度梯度，所以当冰盖重新形成时，基底融化占主导地位。 为了评估湖水的贡献和不断变化的基底热梯度，我们提出了一个综合方案，将卫星图像分析，一系列的侦察航空地球物理剖面恢复湖区和安装连续GPS站点恢复湖。 这种分析和新的数据将使我们能够（1）产生恢复湖区的速度场，（2）绘制由于加速度触发的变薄，基底融化和冻结导致的湖泊冰厚度变化，（3）确定恢复湖的深度和可能的构造起源，以及（4）确定这些湖泊随时间的稳定性。 这些基本数据集将使我们能够推进我们对冰下湖泊如何触发流动的理解。 该项目的智力价值在于，它将是第一次对触发冰流形成的冰流进行系统分析。 这项工作对未来冰盖行为的建模，气候突变的地质记录和冰下湖泊的寿命具有深远的意义。该项目的更广泛影响是通过参与研究的本科生，教师教育计划的正式演示以及主要科学博物馆正在进行的公共宣传工作，接触所有年龄段的学生。冰下南极湖泊环境正在成为2007-2009国际极地年期间首要的主要勘探前沿。

Bell/0636883This award support a project to study the role that subglacial water plays in the overall stability of major ice sheets. An estimated 22,000 km3 of water is currently stored within Antarctica's subglacial lakes. Movement of this water occurs through a complex and largely inferred drainage system in both East and West Antarctica. Geomorphic evidence for the catastrophic drainage of subglacial lakes documents repeated events. These major flood events appear to have drained the largest subglacial lakes situated in the relatively stable interior of the East Antarctic ice sheet. Emerging evidence suggests there is a close connection between significant subglacial lakes and the onset of the Recovery Ice Stream one of the largest in East Antarctica. Our preliminary analysis of the Recovery Lakes region, East Antarctica suggests a direct linkage between lakes and streaming ice flow, specifically the 800 km long Recovery Ice Stream and its tributaries. Located just upslope of the Recovery Ice Stream, the Recovery Lakes Region is composed of 3 well-defined lakes and a fourth, ambiguous, 'lake-like' feature. While other large lakes have a localized impact on ice surface slope, the Recovery Lakes Region lakes are coincident with an abrupt regional change in the ice sheet surface slope. Satellite imagery demonstrates that the downslope margin of this lake area contains distinct flow strips and crevasses: both indicative of increasing ice velocities. The discovery of a series of large lakes coincident with the onset of rapid ice flow in East Antarctica clearly links subglacial lakes and ice sheet dynamics for the first time. The evidence linking the onset of streaming in the Recovery Drainage Ice Stream to the series of large subglacial lakes raises the fundamental question: How can subglacial lakes trigger the onset of ice streaming? We advance two possible mechanisms: (i) Subglacial lakes can produce accelerated ice flow through the drainage of lake water beneath the ice sheet downslope of the lakes. (ii) Subglacial lakes can produce accelerated ice flow accelerated ice flow by modifying the basal thermal gradient via basal accretion over the lakes so when the ice sheet regrounds basal melting dominates. To evaluate the contribution of lake water and the changing basal thermal gradient, we propose an integrated program incorporating satellite imagery analysis, a series of reconnaissance aerogeophysical profiles over the Recovery Lake Region and the installation of continuous GPS sites over the Recovery Lakes. This analysis and new data will enable us (1) to produce a velocity field over the Recovery Lakes Region, (2) to map the ice thickness changes over the lakes due to acceleration triggered thinning, basal melting and freezing, (3) determine the depth and possible the tectonic origin of the Recovery Lakes and (4) determine the stability of these lakes over time. These basic data sets will enable us to advance our understanding of how subglacial lakes trigger the onset of streaming. The intellectual merit of this project is that it will be the first systematic analysis of ice streams triggering the onset of ice streams. This work has profound implications for the modeling of ice sheet behavior in the future, the geologic record of abrupt climate changes and the longevity of subglacial lakes. The broader impacts of the project are programs that will reach students of all ages through undergraduates involved in the research, formal presentations in teacher education programs and ongoing public outreach efforts at major science museums. Subglacial Antarctic lake environments are emerging as a premier, major frontier for exploration during the IPY 2007-2009.