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

这个项目评估了快速移动的冰川或冰流底部的水和岩石/冰的性质在控制其运动方面所起的作用。在表面融化有限的南极洲，冰流经接地带(陆地上的冰在那里分离并开始漂浮在海水上)的速度控制着冰川导致海平面上升的速度。冰流的速度强烈地依赖于来自床面的阻力，因此了解控制流动阻力的过程对于预测冰盖质量平衡是至关重要的。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力学，其中包括对快速冰移的基本控制。钻探以获得对大量区域的基本性质的直接观察是昂贵得令人望而却步的。该项目使用被动震源地震学来“听”和分析水在冰/床界面产生的声音和/或粘性点，以评估基础切应力在冰流动力学中所起的作用。由于极地科学对科学家和公众都很有吸引力，它是一个极好的话题，可以让各级学生接触到重要的科学概念和过程。与这项研究相结合，将开发极地科学教材，供从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大学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。这门课程将与梅萨学校计划(Mesa School Program)共享，该计划是圣克鲁斯和蒙特利县的一个组织，经营着课后科学俱乐部，由当地几所以少数民族和贫困人口为主的初中和高中的教师领导。这项提议将根据先前的合同建立的惠利安冰川(WIS)的钻孔和地面地球物理监测期再延长两年。来自WIS台网的数据表明，微震活动揭示的基本非均质性在100‘S米的尺度上表现出变化。延长的观察期将允许在与当地冰层厚度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。由于冰的速度很快(300米/年)，在延长的3年运行期内，单个测量位置将移动约1公里，从而能够在冰通过粘性地点和河床中的其他特征(例如，冰川补丁或冰川下水体)时持续监测地震排放。超过1公里长的观测将有助于弥合目前对基本条件的观测中的一个关键差距，即在钻孔中进行的极端局部观测与从冰面速度数据的反演推断的基本剪应力的远程观测之间的一个关键差距。

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.