Ice-sheet radar layering and the development of preferred crystal orientation fabrics between Lake Vostok and Ridge B, central East Antarctica

Airborne radar data at 60 MHz are analysed to examine the flow of ice between the Ridge B ice divide and the Vostok Station subglacial lake in central East Antarctica. Interferometric SAR ice surface velocities show how three radar transects are aligned along the general direction of ice flow. Internal layering within the ice sheet is used to determine changes in the vertical component of ice flow along the transects. These data indicate ice sheet flow is related strongly to subglacial topography. In one transect, ice flows in a conventional base-parallel manner down a relatively uniform subglacial slope in the direction of ice flow. In the other two transects, internal layers show the flow of ice over a large subglacial hill upstream of Lake Vostok. Across the stoss face of this subglacial hill, analysis of the radar reflections from internal layers show that layers of ice with a preferred crystal orientation are likely to develop. This process results in layers of ice with a preferred crystal fabric across Lake Vostok at ice depths greater than ~2.8 km. Evidence to support our analysis comes from the Vostok ice core where layers of ice with noticeable crystal alignment are abundant at ice depths greater than 2.7 km.