INSIGT: Investigating Shear-margin Interactions with Grounding-line Transitions

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Antarctica is losing most of its mass through rapid and localized ice flow in outlet glaciers and ice streams. While the position and width of outlet glaciers are often largely controlled by the underlying landscape (e.g., ice flow through gaps in mountains), ice streams flow mostly over sedimentary basins with little or no topographic control on their lateral boundaries. Despite these differences, both ice streams and outlet glaciers are potentially prone to unstable retreat. One of the key mechanisms responsible for this rapid ice loss is the marine ice-sheet instability, in which continued retreat may be induced in areas where the bathymetry slopes inland. This instability has been primarily studied for outlet glaciers with lateral topographic bounds on ice flow. Consequently, this project explores the effect and applicability of the marine ice-sheet instability to ice streams without those topographic bounds on their margins.The goal of this project is to understand whether and how the mechanism of the marine ice-sheet instability applies to ice streams. To achieve this goal, the team will study how ice streams respond to the retreat of the grounding line, where ice loses contact with the bed and starts floating in the ocean. The team will focus on understanding the coupling between grounding-line retreat and ice-stream lateral boundaries rather than initiation of grounding-line retreat. It is hypothesized that both the width and flow speed of ice streams would be affected by retreat, because ice-stream dynamics are extremely sensitive to the force-balance between the bed, margins, and driving stress. More specifically, the team hypothesizes that the bed slope is less relevant in the case of ice streams than it is for outlet glaciers, because ice streams have the potential to widen in response to retreat, exacerbating ice loss even in the absence of a landward sloping bed. This mechanism, however, depends on the resistance to both widening and flow acceleration, which is sensitively dependent on the subglacial hydrology between ice and the sedimentary layer underneath. The team will test its hypothesis through a customized numerical modeling approach developed for this purpose and will compare model predictions to observational constraints from past ice flow in the Siple Coast region of West Antarctica.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.