Numerical simulations of the ice flow dynamics of the Brunt Ice Shelf – Stancomb Wills Ice Tongue System

Ice shelves play an important role in determining regional ocean properties and in modulating ice flux from land to sea. Their dynamics are complex, however, and localised rifts and zones of weakness can have a significant but poorly understood effect on flow and ultimately on the integrity of the shelf. The Brunt Ice Shelf (BIS)- Stancomb Wills Ice Tongue (SWIT) System, situated on the Caird Coast, Oates Land, Antarctica, is characterised as a thin, unbounded ice shelf with a highly heterogeneous structure. In contrast to most ice shelves, icebergs calve along much of the grounding line but are trapped and subsequently bound together by sea ice. This calf-ice / sea-ice aggregate makes up a large part of the Brunt Ice Shelf in particular, and this heterogeneity makes the BIS-SWIT a good test case for investigating the importance of weak zones in shelf dynamics. We applied a diagnostic, dynamic/thermodynamic ice-shelf model to simulate the present flow of the ice shelf that results from the ice-thickness distribution, the influx at the grounding line and the surface and bottom temperature. We then compared the model results with flow velocities measured by Synthetic Aperture Radar feature tracking. We found that our simulations were clearly improved by the use of a high- resolution ice thickness distribution on the heterogeneous ice shelf calculated from ICESat surface elevation data using an assumption of hydrostatic equilibrium. We then assessed the model’s sensitivity to ice thickness, inflow velocities and a flow enhancement factor that parameterises the role of sea ice, whose mechanical properties are known to be significantly different from those of meteoric ice. We found that the numerical simulations were improved by incorporating the detailed variations in shelf structure. Simulated flow velocities on either side of rifts in the ice shelf became decoupled as we softened the sea ice within the rifts. On a larger scale, we found that soft sea ice can lead to a decoupling of the movement of the Stancomb-Wills Ice Tongue and the Brunt Ice Shelf. When we simulated a regime where sea ice was absent, ice shelf flow speeds increased along the western edge of the SWIT ice front, in general agreement with observations made in just such a sea- ice-free dynamic regime that occurred in

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