Subglacial Lake Whillans - Seismic observations of a shallow active reservoir beneath a West Antarctic ice stream

Active subglacial lakes concentrate the distribution of water beneath ice sheets in both space and time. Seismic and surface observations from Subglacial Lake Whillans (SLW), West Antarctica, reveal that this active lake forms a persistent, albeit fluctuating, reservoir beneath Whillans Ice Stream. Imaging and phase observations using active-source seismic data show that SLW is a perpetually shallow feature. When surveyed near its low-stand, a water column was resolvable by seismic techniques along only 5. km of the 45. km profiled, with a maximum depth of less than 8. m. Satellite altimetry shows that the high-stand adds no more than 3-4. m to this. This water column presents a suitable drill site at S 84.240 ° W 153.694 ° Elsewhere, the majority of the bed appears wet with soft sediment or water thicknesses of less than the imaging resolution of our data of approximately 2. m. The surface expression of the active lake, previously revealed by ICESat elevation data and image differencing, generally corresponds to the seismic estimate of soft sediment or water, with notable exceptions occurring at the upstream and downstream ends of the lake. These exceptions indicate that SLW's water column is very shallow or absent in places at low-stands, or has disconnected or transiently active and inactive portions.