Greenland Ice Sheet dynamic response to inland expansion of a hydrologically-active ice-sheet bed

格陵兰冰盖对海平面上升的贡献正在加速，部分原因是冰盖流动的加速。冰盖表面的融化可以到达冰的底部并改变冰流，但这种影响是复杂的，人们对此知之甚少。随着气候变暖，经历表面融化的冰面面积向内陆扩张，重要的问题包括更大面积的冰盖是否会被注入融化的水，以及这是否会导致更快的流动。这个为期三年的项目将测量格陵兰冰盖上冰盖上湖泊和山丘的横断面上的冰盖速度和变形，这些湖泊和山丘提供了地表到海床的融水通道。这些冰上测量将使人们能够更好地了解控制水进入新的冰上湖泊形成区域的冰盖床的过程，重点是水力破裂(水驱动的破裂)过程。该项目将支持Lamont-Doherty地球观测站科学家和纽约市教育部之间的教育伙伴关系，以开发和实施一系列课堂课程，重点是应用于格陵兰冰盖和纽约市环境的地球物理学。该项目将培养一名研究生，并支持一名博士后科学家和一名早期职业科学家。目前地表熔体的内陆迁移在观测时代是前所未有的。预测冰盖对冰盖床表面融化水注入的动态流动响应的一个根本挑战是量化冰盖中上部消融带中新生的冰上湖泊形成区域的应力。在该项目中，将在16个月内部署全球定位系统(GPS)和自主相敏雷达单元，以测量冰盖表面速度、表面和冰川应变以及中上消融区冰上湖泊和冰山周围的应力瞬变。这些现场数据将与地球物理反向建模技术结合使用，以计算地表和冰盖应力和变形模式，并量化控制水进入冰盖床的过程。这项研究的一个主要目标是解决基本问题，这些问题将推动我们能够描述格陵兰冰盖和南极冰盖的预报冰盖模式中地表到海床融水输送的动态影响。量化在一定范围的冰层厚度和粘性应变率上引发水力破裂或冰川形成所需的应力，可以将这些发现扩展到这些冰盖地面区域的数千个现有和即将到来的湖泊。此外，将冰川应变和表面变形的观测结合起来，有可能改变我们对冰盖变形的理解，因为它允许对弹性模型适合于在短时间尺度上反演冰川表面变形观测这一假设进行经验检验。回答格陵兰冰盖内部是否以及何时会对表面融化做出动态反应的问题，对于预测海平面上升至关重要。学校学生、博士和博士后实习生的参与将扩大对地球科学的参与，并帮助培训下一代跨学科的地球科学家。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Greenland Ice Sheet’s contribution to sea-level rise is accelerating, partly due to the acceleration of ice-sheet flow. Melt from the ice-sheet surface can reach the base of the ice and change ice flow, but this effect is complex and poorly understood. As the climate warms and the area of the ice surface undergoing surface melting expands inland, important questions include whether a larger area of the ice-sheet bed will receive injections of meltwater, and whether this will lead to faster flow. This 3-year project will make measurements of ice-sheet velocity and deformation along a transect of supraglacial lakes and moulins, which provide surface-to-bed meltwater pathways, on the Greenland Ice Sheet. These on-ice measurements will allow improved understanding of the processes controlling water access to the ice-sheet bed in regions of new supraglacial lake formation, with a focus on the process of hydro-fracture (water-driven fracture). The project will support an educational partnership between Lamont-Doherty Earth Observatory scientists and the New York City Department of Education to develop and implement a series of classroom sessions focused on geophysics applied to the Greenland Ice Sheet and New York City environments. This project will train one graduate student and support a postdoctoral scientist and an early career scientist.The current inland migration of surface melt is unprecedented in the observational era. A fundamental challenge in predicting the ice sheet’s dynamic flow response to the injection of surface meltwater at the ice-sheet bed is quantifying stresses in areas of nascent supraglacial lake formation in the mid- to upper-ablation zone of the ice sheet. In this project, Global Positioning System (GPS) and autonomous phase-sensitive radar units will be deployed over a 16-month period to measure ice-sheet surface velocity, surface and englacial strain, and stress transients around supraglacial lakes and moulins in the mid- to upper-ablation zone. These field data will be used in conjunction with geophysical inverse modeling techniques to compute surface and englacial stress and deformation patterns and to quantify the processes controlling water access to the ice-sheet bed. A major goal of the research is to address fundamental questions that will move us towards being able to describe the dynamic impact of surface-to-bed meltwater transit in prognostic ice-sheet models for both the Greenland Ice Sheet and Antarctic Ice Sheet. Quantifying the stresses necessary to initiate hydro-fracture or moulin formation over a range of ice thicknesses and viscous strain rates allows for the extension of these findings to thousands of existing and forthcoming lakes on grounded regions of these ice sheets. Moreover, combining observations of englacial strain and surface deformation has the potential to transform our understanding of ice-sheet deformation, by allowing an empirical test of the assumption that an elastic model is appropriate for inverting observations of surface deformation of glacial ice on short timescales. Answering the question of whether, and when, the Greenland Ice Sheet interior will respond dynamically to surface melt is vital for predicting sea-level rise. The engagement of school students and doctoral and postdoctoral trainees will broaden participation in the Earth Sciences and help train the next generation of interdisciplinary geoscientists.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.