WISSARD at Subglacial Lake Whillans, West Antarctica: scientific operations and initial observations

Abstract

A clean hot-water drill was used to gain access to Subglacial Lake Whillans (SLW) in late January 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, a conductivity-temperature-depth (CTD) probe, a Niskin water sampler, an in situ filtration unit, three different sediment corers, a geothermal probe and a geophysical sensor string. Our observations confirm the existence of a subglacial water reservoir whose presence was previously inferred from satellite altimetry and surface geophysics. Subglacial water is about two orders of magnitude less saline than sea water (0.37-0.41 psu vs 35 psu) and two orders of magnitude more saline than pure drill meltwater (<0.002 psu). It reaches a minimum temperature of -0.558C, consistent with depression of the freezing point by 7.019 MPa of water pressure. Subglacial water was turbid and remained turbid following filtration through 0.45 mm filters. The recovered sediment cores, which sampled down to 0.8 m below the lake bottom, contained a macroscopically structureless diamicton with shear strength between 2 and 6 kPa. Our main operational recommendation for future subglacial access through water-filled boreholes is to supply enough heat to the top of the borehole to keep it from freezing.

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

“…The drill site was placed over the deepest portion of the lake as inferred by the area with the lowest hydropotential, largest surface elevation change and deepest measured surface depression [55]. At the time of drilling, the lake was in the process of refilling, following a low stand in 2010 [32]. Using a borehole camera and a conductivity, temperature and depth system (CTD; SBE 19plus V2 SeaCAT Profiler; Seabird Electronics), the thickness of the liquid water column at the time of sampling was estimated to be between 1.6 and 2.2 m [32].…”

“…(a) Water column structure SLW was penetrated after drilling through 802 m of glacier ice [32]. The drill site was placed over the deepest portion of the lake as inferred by the area with the lowest hydropotential, largest surface elevation change and deepest measured surface depression [55].…”

“…In January 2013, SLW became the first subglacial Antarctic lake to be drilled into and sampled directly, a major milestone of the WISSARD project [32]. Although refrozen lake water has recently been collected from Subglacial Lake Vostok [33], the extent of contamination due to mixing of lake water with the borehole drilling fluid was extensive, preventing an unequivocal analysis [34].…”

“…Borehole instrumentation and deployment are described in detail elsewhere [32] and are the focus of other articles in this issue [31]; we include a brief description of the tools used to collect samples for biological and geochemical analyses. Bulk water samples were collected using a 10 l Niskin sampler (General Oceanics, Inc.) from the approximate centre of the water column (approx.…”

“…The approach of the WISSARD project was to clean all instruments entering the lake with a 3% hydrogen peroxide solution, UV-irradiate all cables and hoses deployed down the borehole and reduce microorganisms in the drilling water using a combination of filtration and UV exposure [46]. To minimize the potential for water exchange, the borehole water level was lowered prior to penetration into the lake cavity, which allowed lake water to enter the borehole and prevented drilling water from entering the lake proper [32]. A hot water drill and water treatment unit were designed specifically for the WISSARD project [47,48].…”