Ice-dynamic conditions across the grounding zone, Ekströmisen, East Antarctica

Abstract

AbstractA detailed investigation was performed of ice-dynamic conditions across the southern grounding zone of Ekströmisen, at the mouth of a regular East Antarctic outlet glacier not characterized by ice-streaming. Accurate field measurements along a profile 20 km long served as input in a two-dimensional numerical ice-flow model in order to calculate the variation of stress, strain rate and velocity with depth. The model results point to a sharp transition between the mechanics of grounded and floating ice, with a transition zone of only a few km between the two. Vertical shear, most of it near the base, was found to be the dominant flow mechanism in grounded ice. This part is also characterized by a distinct succession of surface undulations which are in turn controlled by variations in resistive stresses at the bottom. The associated phase shift between driving stress and basal drag was found to be accommodated by differential longitudinal pushes and pulls at the base. The flow in the upper half of the profile, on the other hand, is extensive everywhere. The adjacent ice shelf is characterized by small stress and velocity gradients in both the vertical and horizontal directions of the vertical section, and therefore has little deformation. A derived longitudinal deviatoric normal stress of only one-tenth of the value required for freely floating ice shelves reflects a large back-stress originating from friction along the side-walls of the narrow embayment.