Ice Sheet System Model (ISSM) studies of controls on stability of Thwaites and Pine Island Glaciers, West Antarctica

Targeted modeling of West Antarctica's Thwaites Glacier (TG) and Pine Island Glacier (PIG) using the open-source JPL-UCI Ice Sheet System Model (ISSM) shows that future behavior of these glaciers is sensitive to the geographic pattern as well as total amount of ice-shelf loss caused by changes in oceanic conditions, and that this sensitivity depends on the flow law of the glacier beds. Using ISSM's novel moving-front capability, simulated responses of PIG and TG to initial loss of targeted regions of their floating ice shelves highlight areas of particular importance to each glacier's stability. Prognostic runs show sensitivity to regrowth or continued absence of ice shelves following removal, highlighting the need for realistic oceanic forcing. We report progress in developing and integrating a parameterization for sub-ice-shelf melt to better prescribe sustained oceanic forcing in decadal simulations while maintaining computational efficiency. We also confirm and extend earlier work that response to ice-shelf loss depends strongly on the basal rheology of grounded ice. On short timescales, nearly plastic beds tend to stabilize by limiting near-coastal thinning that would allow grounding-line retreat from its stabilizing bedrock ridge into deep interior basins, whereas nearly viscous beds localize thinning near the coast, triggering instability and grounding-line retreat. However, while the initial stability provided by a more-nearly plastic bed limits retreat, rapid transfer of these stresses upstream results in loss of more volume of grounded ice on multi-decadal timescales than in simulations based on more-nearly viscous beds. These results indicate a tradeoff between initial and sustained stability as a function of bed character.