. "4 Drilling and Sampling Technologies and the Potential for Contamination." Exploration of Antarctic Subglacial Aquatic Environments: Environmental and Scientific Stewardship. Washington, DC: The National Academies Press, 2007.
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Exploration of Antarctic Subglacial Aquatic Environments: Environmental and Scientific Stewardship
be used for sample retrieval from a subglacial lake if certain precautions are taken to ensure that the drilling fluids do not enter the subglacial aquatic environments.1
Using hot water to melt holes into the ice is a well-established technique that has been used by several countries such as the United States (AMANDA, ICECUBE, Caltech), Australia, Germany, and the United Kingdom. Hot-water drills operate by pumping hot water from a heater through a hose under high pressure to a drill head, which melts the ice. This technique generates a hole filled with water, which is pumped to the ice surface where it is reheated and pumped back into the hole. The drawbacks of this technique are that holes are open for only a few hours because the water refreezes, the hole closes, and no cores are recovered.
Keeping holes open for more than a few hours necessitates constant reaming and input of heat, which requires significant amounts of fuel. Ideally, such holes could be considered clean because the water used to melt the holes comes from the melted ice itself and is constantly recirculated through the heaters and high-pressure pumps. However, this circuit through machinery is also a possible source of contamination. Soot or materials dissolved from the walls of the high-pressure hose may contaminate the waters that are pumped back into the hole.2 These potential contaminants could be removed by introducing nanotechnology filters in the steam path and through the high-pressure (e.g., 8-10 MPa) steam itself. It is even conceivable to introduce a full autoclave system into the water circuit. Although this technique has been used to quickly drill several kilometers of ice and may be able to access some subglacial aquatic environments, more method development will be needed for this technique to achieve the ice depths that are required to reach many subglacial aquatic environments located beneath thicker ice.
Melt or thermo-probes represent another technology that shows promise to access subglacial aquatic environments. It should be noted however, that to date, the melt probe concept has not yet achieved this. Originally designed by Philbert & Philbert as a system to remotely measure temperature within the Greenland ice sheet, melt probes have so far reached a maximum depth of about 1600 m. The probes have a heated element at the tip, which melts ice as it descends. The water refreezes behind the probe, which is tethered to the surface via cable. Such melt probes could conceivably reach subglacial aquatic environments in a sterile fashion. Once in position, these probes could collect remote measurements and provide data communication with the surface.
Despite precautions, drilling fluids may enter the subglacial aquatic environments, but these fluids will most likely not adversely affect the environment. For example, if one takes the diameter of the Vostok core hole as 15 cm and 4000 m as its length, the hole volume is roughly 70 m3. Based on geophysical surveys, the volume of Lake Vostok has been estimated as 5.4 × 1012 m3 (Studinger et al. 2004). Thus, if the full fluid content of such a core hole was injected into a well-mixed lake of this volume, the dilution factor would be 1 × 10−11.
Dissolution of the high-pressure hose may result from interaction with the high-pressure, high-temperature steam generated from the heaters and pumps.