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/冰属性在控制其运动中的作用。在南极洲，表面融化是有限的，通过接地带（陆地上的冰分离，并开始漂浮在海水上）的冰流速度控制着冰川对海平面上升的贡献速度。冰流的速度很大程度上取决于河床的阻力，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提高对冰盖动力学的了解，其中包括对快速冰运动的基本控制。通过钻井直接观察大片地区的基本性质是非常昂贵的。本项目使用被动震源地震学“聆听”和分析水流和/或冰/床界面粘点产生的声音，以评估基底剪切应力在冰流动力学中的作用。因为极地科学对科学家和公众都很有吸引力，所以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，将开发极地科学教育材料，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州立数学与科学暑期学校（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项目共享。梅萨学校项目是圣克鲁斯和蒙特利县的一个组织，在当地几所以少数民族和贫困人口为主的初中和高中，由教师领导课后科学俱乐部。该提案将根据之前的合同建立的Whillians冰流（WIS）的井眼和地面地球物理监测期限延长了2年。来自WIS网络的数据表明，微震活动揭示的基本非均质性在100米尺度上表现出变化。延长的观察期将允许在与当地冰厚相当的关键长度尺度上详细描述冰盖床的地震特性。由于冰速度快（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，从而可以连续监测冰在粘点和床上其他特征（例如，农田或冰下水体斑块）上移动时的地震发射。在~1km长度尺度上的观测将有助于弥合目前对基础条件观测中极为局部的钻孔观测与从冰面速度数据反演推断的基底剪应力远程观测之间的关键差距。

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.