Channelised Subglacial Hydrology Modulates West Antarctic Ice Stream Basal Conditions and Flow

Abstract:

Ice-sheet models show a coincidence between ice flux and basal water-flow maxima, as water at the bed of an ice sheets acts generally to lubricate the basal interface. Hydrological flow paths support this view with ice and basal-water drainage basins being well-aligned. At the scale of an individual ice stream, however, we reveal a significant offset of this alignment. Airborne geophysical data across the trunk of the Institute Ice Stream reveal how subglacial hydrology acts to subdue ice flow in two ways: first, by removing basal sediment, which decreases opportunity for the deformation of basal material and increases basal roughness; and, second, by reducing basal water pressures. The macro flow of basal water beneath the ice stream is known well from high-resolution bed elevation data and satellite imagery, which reveal well-organised water flow along the Robin Subglacial Basin, terminating at the grounding line as a channel carving upwards into the adjacent ice shelf. The highest ice flow is offset from this channelized zone, however. Maximum velocities are located where the bed is very smooth and radio-echo returns are strong; consistent with a dilated weak sedimentary material at the ice stream bed. The geophysical evidence is consistent with the removal of basal sediment from the deepest regions of the Robin Subglacial Basin by the action of water and illustrates how accumulation of sedimentary material from ice streams is not necessary a precise locator for maximum ice-flow velocities at the scale of individual ice streams.

The figure shows a radar section across the Institute Ice Stream, West Antarctica, revealing two modes of basal environment. One is flat and smooth, indicative of a soft wet bed. The other is rougher, as a consequence of the removal of basal material and water channelisation. This latter region is located in the deepest regions of the Robin Subglacial Basin. The former region is located beneath the highest ice flow speeds.