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.

了解冰川和冰盖的冰损失以及由此造成的海平面上升至关重要。格陵兰和南极冰盖，以及山地冰川，主要通过冰河排放;因此，了解是什么控制了这些冰河中发生的流动类型，对于了解和预测海平面上升至关重要。人们认为影响冰流的重要因素之一是流动冰川两侧冰的内部强度。反过来，这种粘性强度可能会受到冰川中冰晶微观结构的影响。研究人员建议在阿拉斯加山脉东部的贾维斯冰川上详细研究这些关系，最终目标是能够在冰川流动的数值模型中代表微观结构的影响。为此，研究人员将首先使用表面速度测量，从地面穿透雷达获得的冰川几何形状知识，以及数值建模来确定钻探地点。然后，他们将收集横向和垂直流动梯度的表面到床芯。从钻孔中获得的速度和温度测量值将补充表面测量值，并使调查人员能够制作更复杂的三维数值模型，以测试研究区域内流动模式对机械结构的敏感性。他们将比较微观结构（例如，粒度分布，晶体结构）在冰芯的原位和模拟的速度和温度。虽然实验表明，晶体结构的强度和方向的变化可能导致流动强度的差异高达10倍，但对流动冰的微观结构结构的原位观测研究很少;大多数对冰微观结构的研究来自冰分裂，那里的流速最慢。在该项目结束时，研究人员的目标是确定（1）在研究区域形成的结构在多大程度上是基于冰运动学可预测的，以及（2）通过数值模型计算的测量的晶体取向结构强度，粒度，温度和冰粘度之间的关系。结构和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确定冰的流变结构的更有力的方法。或者，粘性强度和织物之间缺乏强有力的联系，表明其他因素对流变性能有重要的控制作用。因此，无论微观结构和粘性强度之间的相关性如何，拟议项目的结果都应提高对流冰物理规律的定量理解，并改善未来冰质量平衡的预测。该项目将支持和参与研究生和本科生。该项目的数值模型将被开发成一个公开的基于网络的图形用户界面，供其他研究人员和课堂使用。