Sensitivity of the Amundsen Sea Embayment to changes in external forcings using Automatic Differentiation
Abstract
Thwaites, Pine Island Glacier and other ice streams of the Amundsen Sea Embayment in West Antarctica have been changing dramatically over the past decades. There is broad agreement that the intrusion of warm Circumpolar Deep Water into sub-ice shelf cavities is the primary driver of these changes but it remains unclear where these ice shelves are most sensitive to melt, or whether other processes could cause further or more dramatic mass loss. Here, we analyze the sensitivity of two transient, high-resolution ice sheet models (STREAMICE and ISSM) to changes in boundary conditions and external forcing. We rely on automatic differentiation to derive the sensitivity of the volume above floatation after 3 years of simulation to changes in ocean-induced melt rates, in the ice rate-factor, in basal friction, and changes in surface mass balance. The sensitivity maps highlight the regions that are most at risk to changes in any of these forcings at the scale of the model mesh, i.e., a few hundred meters close to the grounding line to a few kilometers inland. We find that changes in basal melt close to the grounding lines, close to ice rises or along shear margins have a very large impact on the final volume above floatation, while other regions are insensitive to changes in melt rates. The sensitivity of the model to basal friction is large close to the grounding line of Pine Island glacier but limited in other regions. If the sensitivity to changes in the rate factor is large along the shear margins of Pine Island, it is close to zero over the margins of Thwaites glacier, which suggests that the glacier would not be sensitive to a weakening of its margins, which calls into question a hypothesis that is frequently invoked in the literature. The sensitivity to surface mass balance is remarkably uniform. This exercise highlights the regions that are most at risk to changes in external forcings, but also which process should be properly captured by numerical models in order to accurately project the future response of this sector.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMC057...06M
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHERE;
- 0762 Mass balance;
- CRYOSPHERE;
- 0774 Dynamics;
- CRYOSPHERE;
- 4207 Arctic and Antarctic oceanography;
- OCEANOGRAPHY: GENERAL