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The Subglacial Antarctic Lakes Scientific Access (SALSA) Project accessed Mercer Subglacial Lake using environmentally clean hot-water drilling to examine interactions among ice, water, sediment, rock, microbes and carbon reservoirs within the lake water column and underlying sediments. A ~0.4 m diameter borehole was melted through 1087 m of ice and maintained over ~10 days, allowing observation of ice properties and collection of water and sediment with various tools. Over this period, SALSA collected: 60 L of lake water and 10 L of deep borehole water; microbes >0.2 μm in diameter from in situ filtration of ~100 L of lake water; 10 multicores 0.32–0.49 m long; 1.0 and 1.76 m long gravity cores; three conductivity–temperature–depth profiles of borehole and lake water; five discrete depth current meter measurements in the lake and images of ice, the lake water–ice interface and lake sediments. Temperature and conductivity data showed the hydrodynamic character of water mixing between the borehole and lake after entry. Models simulating melting of the ~6 m thick basal accreted ice layer imply that debris fall-out through the ~15 m water column to the lake sediments from borehole melting had little effect on the stratigraphy of surficial sediment cores.
The WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) traversable hot-water drill system was designed to create various-diameter ice boreholes to a depth of >800 m, with most major components being controllable from a single user interface. The drill control system operates four low-pressure pumps for water generation and circulation, two hot-water generation units containing a total of six diesel burner modules with integrated high-pressure pumps, three winches (one with independent level-wind motor), a four-motor linear traction drive, and a large number of analog and digital sensors to monitor system performance and cleanliness. Due to development time constraints the control system design focused on utilizing commercial off-the-shelf components, while being highly modular, easily expandable and rapidly deployable. Additional emphasis was placed on providing redundant manual operator controls and maintaining a low degree of system automation to avoid dependence on software control loops for first-season deployment. The result of this design paradigm was a control system that was taken from concept to full operation in <6 months, successfully performing in the field without insurmountable problems.
A new, clean, hot-water drill system (HWDS) was developed by the Science Management Office, University of Nebraska-Lincoln, for use in the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project to gain access to Subglacial Lake Whillans beneath ∼800 m of ice in West Antarctica. One primary borehole was drilled into the basal ice environment of Subglacial Lake Whillans during the initial field season in 2012/13. This paper describes the process of designing, fabricating, assembling, shipping, testing, commissioning and traversing the WISSARD HWDS leading up to the first scientific use of the system.
Successful hot-water drilling in the Antarctic is predicated on utilization of the abundant water supply available in the form of the Antarctic ice sheet. For WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) field operations, a snowmelting system was developed that could adequately provide water for a 1000 kW hot-water drill. The system employs ∼100 kW of waste heat from a 225 kW generator to melt snow for initial water (known as seed water) to prime the drill’s high-pressure pumps and water heaters; once the water heaters can be engaged in snowmelting, enough water can be supplied directly to the WISSARD drill to successfully melt a 40 cm diameter hole through 800 m of ice.
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