Sequential Stagnation of Kamb Ice Stream Induced by Changes in Subglacial Hydrology

Abstract:

Ice stream dynamics remain an important unknown in quantifying the future mass flux from ice sheets. On the Siple Coast of West Antartica, ice streams lack distinct topographic control and have exhibited large-scale rearrangement on decadal to centennial time scales. The shutdown of Kamb Ice Stream and slowing of Whillans Ice Stream provide an opportunity to study the mechanisms governing ice-stream stability and assess their potential response to climatic perturbations. Here, we aim to evaluate possible mechanisms that lead to continuous and discontinuous margin migration within the context of the Siple Coast.

The variable behavior of Siple Coast ice streams depends strongly on the coupling between till rheology, ice rheology, and shear margin position. We capture these feedbacks through a time-dependent 2D thermo-mechanical model that resolves the self-consistent margin position. We assume a plastic till, where yield strength is strongly dependent on pore pressure. This coupling results in spatially variable basal strength that evolves in time based on the presence and development of subglacial water systems. Furthermore, we link melt production in the ice column to pore pressure in the till, to determine how englacial melt production may affect margin position and stability. The model can therefore provide constraints on basal strength distributions that facilitate continuous and discontinuous margin migration.

This study focuses on the Duckfoot region of Kamb Ice Stream, a section of ice near the grounding line that is thought to have experienced discontinuous margin migration. Retzlaff and Bentley [1993] suggest that a film to channel collapse may have initiated stagnation, while other studies suggest water piracy, variations in driving stress, and grounding of the ice shelf. We present model results for different migration and stagnation hypotheses and compare our results to radar data from Catania et al. [2006]. We demonstrate that changes in the efficiency of the subglacial drainage system are likely the explanation for sequential stagnation of Duckfoot and eventual shutdown of Kamb Ice Stream. We also discuss implications to the slowing of Whillans Ice Stream and investigate surface expressions of channelized drainage development.