Greenland Ice Sheet Dynamic Response to Inland Expansion of a Hydrologically-Active Ice-Sheet Bed

DESCRIPTION: 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.