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

了解冰川和冰盖的冰流失以及由此导致的海平面上升至关重要。格陵兰和南极冰盖以及山脉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，对于理解和预测海平面上升至关重要。在最不为人所知的因素中，被认为是影响冰流的重要因素之一，是流动的冰川两侧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观结构的影响。研究人员建议在阿拉斯加东部山脉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表现微结构的影响。为此，研究人员将首先使用表面速度测量、从探地雷达获得的冰川几何知识和数值建模来确定钻探地点。然后，他们将在横向和垂直流动梯度上收集地表到海底的岩心。从钻孔得到的速度和温度测量将补充地面测量，并使调查人员能够产生更复杂的三维数值模型，以测试流型对研究区域内机械结构的敏感性。他们将把冰芯中的微结构(例如，颗粒大小分布、晶体组构)与现场模拟的速度和温度进行比较。尽管实验表明，结晶组构的强度和取向的变化可以导致流动强度的十倍之差，但对流动冰的微结构结构的现场观测研究很少；大多数对冰微结构的研究来自流动速度最慢的冰隔层。在这个项目的最后，研究人员的目标是确定(1)基于冰运动学在研究区域形成的织物的可预测性程度，以及(2)通过数值模型计算的测量的结晶取向织物强度、颗粒大小、温度和冰粘度之间的关系。组构和粘性强度之间的相关性将表明，雷达和地震各向异性等遥感技术可能成为识别冰流变结构的更强大的方法。另一方面，粘性强度和织物之间缺乏很强的联系，这表明其他因素对流变性起着重要的控制作用。因此，无论微结构和粘性强度之间的相关性如何，拟议项目的结果都应该提高对流动冰物理规律的定量理解，并改善对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，供其他研究人员使用和在课堂上使用。

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.