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的流动，但这种影响是复杂的，人们对其知之甚少。随着气候变暖，经历表面融化的冰面向内陆扩张，一些重要的问题包括：是否会有更大面积的冰盖床接受融水的注入，以及这是否会导致更快的融水流动。这个为期三年的项目将测量格陵兰冰盖上冰面上湖泊和冰穴的速度和变形，这些湖泊和冰穴提供了从地表到河床的融水通道。这些冰上测量将使我们更好地了解在新的冰上湖形成地区控制水进入冰盖床的过程，重点是水力压裂过程（水驱动裂缝）。该项目将支持Lamont-Doherty地球观测站科学家与纽约市教育部之间的教育伙伴关系，以开发和实施一系列侧重于应用于格陵兰冰盖和纽约市环境的地球物理学课堂课程。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。目前的地表融水向内陆迁移是有观测以来前所未有的。预测冰盖对地表融水注入的动态流动响应的一个基本挑战是量化冰盖中上层消融带新生冰上湖形成区域的应力。在该项目中，全球定位系统（GPS）和自主相敏雷达单元将在16个月的时间内部署，以测量冰盖表面速度、地表和冰川应变，以及冰川上湖泊和冰碛周围的应力瞬变。这些实地数据将与地球物理逆建模技术结合使用，以计算地表和冰川应力和变形模式，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一些基本问题，这些问题将使我们能够在格陵兰冰盖和南极冰盖的预测冰盖模型中描述地表到床融水传输的动态影响。在一定的冰层厚度和黏性应变率范围内，量化引发水力破裂或冰穴形成所需的应力，可以将这些发现扩展到这些冰盖地面上数千个现有和即将形成的湖泊。此外，结合冰川应变和地表变形的观测有可能改变我们对冰盖变形的理解，因为我们可以对弹性模型适用于在短时间尺度上反演冰川表面变形观测的假设进行经验检验。回答格陵兰冰盖内部是否以及何时会对地表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、博士和博士后学员的参与将扩大对地球科学的参与，并有助于培养下一代跨学科的地球科学家。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.