A clean hot-water drill was used to gain access to Subglacial Lake Whillans (SLW) in lateJanuary 2013 as part of the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project.Over 3 days, we deployed an array of scientific tools through the SLW borehole: a downhole camera, aconductivity–temperature–depth (CTD) probe, a Niskin water sampler, an in situ filtration unit, threedifferent sediment corers, a geothermal probe and a geophysical sensor string. Our observations confirmthe existence of a subglacial water reservoir whose presence was previously inferred from satellitealtimetry and surface geophysics. Subglacial water is about two orders of magnitude less saline than seawater (0.37–0.41psu vs 35psu) and two orders of magnitude more saline than pure drill meltwater(<0.002psu). It reaches a minimum temperature of –0.558C, consistent with depression of the freezingpoint by 7.019MPa of water pressure. Subglacial water was turbid and remained turbid followingfiltration through 0.45mm filters. The recovered sediment cores, which sampled down to 0.8m belowthe lake bottom, contained a macroscopically structureless diamicton with shear strength between 2and 6kPa. Our main operational recommendation for future subglacial access through water-filledboreholes is to supply enough heat to the top of the borehole to keep it from freezing.
We use CryoSat-2 interferometric satellite radar altimetry over the Mercer and Whillans ice streams, West Antarctica, to derive surface elevation changes due to subglacial lake activity at monthly resolution for the period 2010 to 2013. We validate CryoSat-2 elevation measurements, trends, and spatial patterns of change using satellite image differencing and in situ vertical movement from Global Positioning System (GPS) data. Two subglacial lake discharge events occur in the same subglacial-hydrological catchment within a 9 month period. Using GPS measurements that are spanning the gap between the Ice, Cloud, and land Elevation Satellite and Cryosat-2 missions, we cross-calibrate the two missions to establish the efficacy of CryoSat-2 altimetry to measure dynamic changes on the ice sheets.
Interactions between subglacial hydrology and the ocean make the existence of estuaries at the grounding zones of ice sheets likely. Here we present geophysical observations of an estuary at the downstream end of the hydrologic system that links the active subglacial lakes beneath Whillans Ice Stream to the ocean beneath the Ross Ice Shelf, Antarctica. This subglacial estuary consists of a hydropotential low upstream of the grounding zone, which is linked to the ocean by a hydropotential trough and a large subglacial channel. This subglacial channel, which is imaged using active source seismic methods, has an apparent width of 1 km and a maximum depth of 7 m. The hydropotential trough continues upstream of the grounding zone and results from an along-flow depression in surface elevations. Pressure differences along the trough axis are within a range that can be overcome by tidally induced processes, making the interaction of subglacial and ocean water likely.