PHAST · A physics-based study of ice stream dynamics

Ice streams are river-like corridors of fast flowing ice that account for the vast majority of ice discharge to the ocean in continental ice sheets. Their most outstanding feature is that they can appear spontaneously within a slowly moving ice sheet, self-organize in evenly spaced patterns, and switch on and off over time. Yet, a full explanation of ice stream formation and evolution is one of the longest standing open problems in glaciology. This knowledge gap has precluded fundamental investigations on the role of ice streams in driving ice sheet change, and also casts doubt on the ability of state-of-the-art ice sheet simulation codes to project future sea levels. Recent work by the PI identified an entirely novel class of feedbacks related to the onset of basal sliding which could be the missing ingredient needed to fully explain observed ice stream dynamic behaviors. Drawing on a unique combination of novel glaciological observations, first-principle theoretical work, and ice-sheet-wide numerical simulations, PHAST builds on this insight to: 1. Develop a complete and coherent theory of ice stream spatial and temporal dynamics that clarifies under what environmental conditions these dynamics are to be expected.2. Test the hypothesis that sliding onset physics play a central role in ice stream dynamics through a targeted field experiment.3. Build a new ice sheet simulation code that resolves sliding onset and ice stream margin physics at low computational cost thanks to emerging domain partitioning methods.4. Assess for the first time the sensitivity of Antarctic and Greenland mass loss to ice stream dynamics. By developing new modeling tools and generating process-level understanding across scales ranging from few tens of meters to thousands of kilometers, PHAST will lead the way towards unraveling the complex interplay between internal ice sheet dynamics and climate over timescales ranging from decades to millennia.