Collaborative Research: Influence of natural ice microstructure on rheology in general shear: in-situ studies in the Alaska Range

合作研究：天然冰微观结构对一般剪切流变学的影响：阿拉斯加山脉的现场研究

• 批准号: 1503653
• 负责人: Robert Hawley
• 金额: $ 21.89万
• 依托单位: Dartmouth College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1503653&HistoricalAwards=false
• 关键词: Collaborative; Research; Influence; natural; ice

Understanding the loss of ice from glaciers and ice sheets, and the resulting sea-level rise, is of critical importance. Both the Greenland and Antarctic Ice Sheets, as well as mountain glaciers, discharge primarily though rivers of ice; understanding what controls the type of flow that occurs in these rivers of ice is therefore central to understanding and predicting sea-level rise. Among the least-understood factors that are thought to be important in affecting ice flow is internal strength of the ice near the sides of a flowing glacier. This viscous strength, in turn, may be affected by the micro-scale structure of the ice crystals in the glacier. The investigators propose to examine these relationships in detail on Jarvis Glacier, in the eastern Alaska Range, with the ultimate goal of being able to represent the effects of microstructure in numerical models of glacial flow.To do this, the investigators will first use surface velocity measurements, knowledge of the glacier geometry derived from ground penetrating radar, and numerical modeling to identify a site for drilling. They will then collect surface-to-bed cores across lateral and vertical flow gradients. Velocity and temperature measurements derived from the boreholes will complement the surface measurements and allow the investigators to produce a more sophisticated three-dimensional numerical model to test the sensitivity of flow patterns to the mechanical structure within the study area. They will compare the microstructure (e.g., grain size distribution, crystallographic fabric) in the ice cores to the in-situ and modeled velocities and temperatures. Although experiments suggest that variations in the intensity and orientation of the crystallographic fabric can result in up to a ten-fold difference in flow strength, there are very few in-situ observational studies of the microstructural architecture of streaming ice; most studies of ice microstructure come from ice divides, where flow rates are slowest. At the end of this project, the investigators aim to have determined (1) the degree to which fabrics formed in the study area are predictable based on ice kinematics, and (2) the relationship among measured crystallographic orientation fabric intensity, grain size, temperature, and ice viscosity as calculated through numerical models. A correlation between fabric and viscous strength would suggest that remote sensing techniques such as radar and seismic anisotropy could become an even more powerful method for identifying the rheological structure of ice. Alternatively, the lack of a strong link between viscous strength and fabric indicates that other factors exert significant control on the rheological properties. Therefore, the results of the proposed project, whatever the correlation between microstructure and viscous strength, should improve quantitative understanding of the physical laws governing streaming ice and improve future predictions of ice mass balance. The project would support and involve both graduate and undergraduate students. The project's numerical models will be developed into a publicly available web-based graphical user interface for use by other researchers and in the classroom.

了解冰川和冰盖因冰的损失以及由此产生的海平面上升至关重要。格陵兰和南极冰盖以及山地冰川都主要散发出冰河。因此，了解什么控制了这些冰河中发生的流动类型对于理解和预测海平面上升至关重要。在影响冰流的最不受欢迎的因素中，在流动冰川侧面附近的冰的内部强度。反过来，这种粘性强度可能会受到冰川中冰晶的微尺度结构的影响。调查人员建议在阿拉斯加东部范围内详细研究这些关系，其最终目的是能够在冰川流量的数值模型中表示微观结构的影响。为此，研究人员将首先使用表面速度测量，了解从地面穿透雷达得出的冰川几何形状的知识以及用于识别钻井位点的数值建模。然后，他们将在横向和垂直流动梯度上收集地表到床的核心。从钻孔得出的速度和温度测量值将补充表面测量值，并允许研究人员产生更复杂的三维数值模型，以测试流动模式对研究区域内机械结构的敏感性。他们将比较冰芯中的微观结构（例如晶粒尺寸分布，晶体学织物）与原位和建模速度和温度。尽管实验表明，晶体学织物强度和方向的变化可能导致流动强度差异十倍，但对流冰的微结构结构的原位观察性研究很少。大多数冰微观结构的研究都来自流速最慢的冰层。在该项目的结尾，研究人员的目的是确定（1）根据冰运动学的研究区域中形成的织物的程度，以及（2）测量的晶体学方向织物强度，粒度，温度，温度的关系之间的关系和通过数值模型计算的冰粘度。织物与粘性强度之间的相关性表明，雷达和地震各向异性等遥感技术可能成为识别冰的流变结构的更强大方法。另外，粘性强度和织物之间缺乏牢固的联系表明其他因素对流变特性产生了重大控制。因此，所提出的项目的结果，无论微观结构与粘性强度之间的相关性如何，都应提高对控制冰的物理定律的定量理解，并改善对冰质量平衡的未来预测。该项目将支持并参与研究生和本科生。该项目的数值模型将被开发为公开可用的基于Web的图形用户界面，以供其他研究人员和课堂使用。