Collaborative Research: In Situ Borehole Measurements To Partition The Velocity Of The Greenland Ice Sheet Into Ice Deformation And Basal Sliding Components, 2014-2017

Sliding of an ice mass along its basal boundary is a fundamental component of motion where bed conditions are wet. Estimates of basal sliding generally result from an inverse analysis of observed surface motion using a model assuming Glen's generalized constitutive law for isotropic ice. Evidence suggests that this law does not adequately represent ice deformation, due to a variety of issues including ice thermal variations, preferred fabric, and chemical impurities in the ice. The PIs propose an innovative experimental design to improve our understanding of the ice deformation and sliding. A grid of 9 boreholes, each approximately 750 meters in depth and extending to the bed, will be drilled through the Greenland Ice Sheet and instrumented with more than 675 sensors to observe ice temperature, ice deformation, and basal sliding. Analysis of the resulting data set will yield the full three-dimensional velocity field and full stress and strain rate tensors for a 420x106 cubic meter block of ice. The results will be used to assess and improve the constitutive law and will provide a data set for testing inversion methodologies. The Greenland and Antarctic Ice Sheets contain enough water to cause massive inundation of heavily populated coastal regions and associated infrastructure, if they were to degrade significantly through melting or delivery of icebergs to the coastal ocean. Our ability to predict future sea level rise is hampered by an inability to accurately model glacier dynamics that connect these ice sheets to the ocean. This project will provide data sets and consequent insight into processes that will lead to improved models of glacier dynamics.

当冰床处于湿润状态时，冰体沿基底边界的滑动（basal sliding）是其运动的基本组成部分。基底滑动的估算通常基于采用各向同性冰的格伦广义本构定律（Glen's generalized constitutive law）的模型，通过对观测到的表面运动进行反演分析得到。现有研究表明，受冰体热变化、优选组构以及冰体中化学杂质等多重因素影响，该定律无法充分表征冰体变形。本项目的首席研究员（Principal Investigators，下称PIs）提出了一项创新性实验设计，以深化对冰体变形与滑动机制的认知。研究团队将在格陵兰冰盖（Greenland Ice Sheet）上钻取9个钻孔，每个钻孔深度约750米且直达冰床，并布设超过675个传感器（sensors），用于观测冰体温度、冰体变形与基底滑动。对所得数据集的分析将得到一块420×106立方米冰体块体的完整三维速度场（three-dimensional velocity field）、全应力张量与全应变率张量。该研究结果将用于评估并改进现有本构定律，同时将提供可用于测试反演方法的数据集。
格陵兰冰盖与南极冰盖（Antarctic Ice Sheets）所蕴含的水量，若二者因显著融化或向沿海海域输送冰山而发生大规模退化，足以引发人口稠密的沿海区域及相关基础设施的大规模淹没。当前我们对未来海平面上升的预测能力受限，根源在于无法精准构建连接冰盖与海洋的冰川动力学（glacier dynamics）模型。本项目将提供相关数据集与研究视角，助力改进冰川动力学模型的构建。