Stick-slip motion of an Antarctic Ice Stream: the effects of viscoelasticity

Stick-slip behavior is a distinguishing characteristic of the flow of Whillans Ice Stream. Distinct from stick-slip on northern hemisphere glaciers, which is generally attributed to supraglacial melt, the behavior is thought be be controlled by fast processes at the bed and by tidally-induced stress. However, the connection between stick-slip behavior and flow on longer time scales, if any, is not clear. To address this question we develop a new ice flow model capable of reproducing stick-slip cycles similar to ones observed on the Whillans Ice Plain. The model treats ice as a viscoelastic material and emulates the weakening and healing that are suggested to take place at the ice-till interface. The experiments suggest the long-term ice-stream flow that controls ice discharge to surrounding oceans is sensitive to some aspects of the subglacial environment, such as the bed strength in its strong and weak states, but less so to others, such as ice velocities during the slip phase and factors that regulate it (such as elastic modulus). Additionally we show that viscous ice deformation, traditionally disregarded in analysis of stick-slip behavior, has a strong effect on the timing of slip events, and therefore should not be ignored in efforts to deduce bed properties from stick-slip observations.