High Resolution Heterogeneity at the Base of Whillans Ice Stream and its Control on Ice Dynamics

该项目评估了快速移动的冰川或冰流底部的水和岩石/冰特性在控制其运动中的作用。在南极洲，表面融化是有限的，冰流经接地区（陆地上的冰分离，并开始漂浮在海水上）的速度控制着冰川对海平面上升的贡献率。冰流的速度在很大程度上取决于床的阻力，因此了解控制流动阻力的过程对于预测冰盖质量平衡至关重要。事实上，政府间气候变化专门委员会（IPCC）认识到了这一点，并在其第四次评估报告中指出，对未来全球海平面上升的可靠预测需要更好地了解冰盖动态，其中包括对快速冰运动的基础控制。为了直接观测大面积地区的基底性质而进行钻探，其费用极其昂贵。该项目使用被动源地震学来“倾听”和分析水流和/或冰/床界面处的粘点产生的声音，以评估基底剪切应力在冰流动力学中的作用。由于极地科学对科学家和公众都很有吸引力，因此它是一个很好的话题，可以让各级学生参与重要的科学概念和过程。结合这项研究，将编制极地科学教材，供中学到大学的学生使用。从2015年夏天开始，加州大学圣克鲁斯分校将为加州数学和科学暑期学校（COSMOS）的高中生开设一门新的极地科学课程。该课程将与梅萨学校计划共享，该计划是一个圣克鲁斯和蒙特利县的组织，该组织在当地几所以少数族裔和弱势群体为主的中学和高中开设了由教师领导的课后科学俱乐部。该提案将根据先前的合同对惠利安冰流（WIS）进行的钻孔和地表地球物理监测的时间延长了2年。来自WIS网络的数据表明，基础的不均匀性，揭示了微震，显示出变化超过100米的尺度。延长的观测期将允许在与当地冰厚相当的关键长度尺度上对冰盖床特性进行详细的地震表征。由于快速的冰速度（300米/年），在延长的3年运行期内，单个仪器位置将移动约1公里，从而可以在冰经过粘性点和床中的其他特征（例如，冰碛物或冰下水体的斑块）。超过1公里的长度尺度的观测将有助于弥合目前观测的基础条件之间的一个关键的差距极端本地观测钻孔和远程观测的基础剪切应力从反演冰面速度数据推断。

This project evaluates the role that water and rock/ice properties at the base of a fast moving glacier, or ice stream, play in controlling its motion. In Antarctica, where surface melting is limited, the speed of ice flow through the grounding zone (where ice on land detaches, and begins to float on ocean water) controls the rate at which glaciers contribute to sea level rise. The velocity of the ice stream is strongly dependent on resistance from the bed, so understanding the processes that control resistance to flow is critical in predicting ice sheet mass balance. In fact, the Intergovernmental Panel on Climate Change (IPCC) recognized this and stated in their 4th assessment report that reliable predictions of future global sea-level rise require improved understanding of ice sheet dynamics, which include basal controls on fast ice motion. Drilling to obtain direct observations of basal properties over substantial regions is prohibitively expensive. This project uses passive source seismology to "listen to" and analyze sounds generated by water flow and/or sticky spots at the ice/bed interface to evaluate the role that basal shear stress plays in ice flow dynamics. Because polar science is captivating to both scientists and the general public, it serves as an excellent topic to engage students at all levels with important scientific concepts and processes. In conjunction with this research, polar science educational materials will be developed to be used by students spanning middle school through the University level. Starting in summer 2015, a new polar science class for high school students in the California State Summer School for Mathematics and Science (COSMOS) will be offered at the University of California-Santa Cruz. This curriculum will be shared with the MESA Schools Program, a Santa Cruz and Monterey County organization that runs after-school science clubs led by teachers at several local middle and high schools with largely minority and underprivileged populations. This proposal extends the period of borehole and surface geophysical monitoring of the Whillians Ice Stream (WIS) established under a previous award for an additional 2 years. Data from the WIS network demonstrated that basal heterogeneity, revealed by microseismicity, shows variation over scales of 100's of meters. An extended observation period will allow detailed seismic characterization of ice sheet bed properties over a crucial length scale comparable to the local ice thickness. Due to the fast ice velocity (300 m/year), a single instrumented location will move approximately 1 km during the extended 3 year operational period, allowing continuous monitoring of seismic emissions as the ice travels over sticky spots and other features in the bed (e.g., patches of till or subglacial water bodies). Observations over ~1km length scales will help to bridge a crucial gap in current observations of basal conditions between extremely local observations made in boreholes and remote observations of basal shear stress inferred from inversions of ice surface velocity data.