At present, there is no technology available for retrieval of such melt probes, which precludes using this equipment for sample recovery. The major disadvantage of using melt probes is that they cannot effectively penetrate ice with particulates and may stop or be diverted from the preferred course. As the borehole deepens, these impurities are concentrated within the borehole because there is no way to circulate the fluids away from the probe (SCAR SALE 2006).

Fast Access Drilling

There are options, as yet untried, for rapid access drilling to the bed using technology from oil drilling industries, such as coiled-tube drilling or even wire-line drilling using conventional drill rigs. These technologies, however, are not presently capable of penetrating ice sheets to greater depths and are not suitable for the conditions likely to be encountered during drilling subglacial aquatic environments. These technologies need to be adapted before they can successfully be used to access subglacial aquatic environments. Development of a new ice sheet drilling platform that will provide access to deep samples of ice and subglacial materials and enable fast completion of arrays of boreholes distributed over large areas (tens and hundreds of kilometers in one season) was the focus of a workshop sponsored by the National Science Foundation.3 The FASTDRILL workshop identified four potential drilling platforms, which may be adapted for the purpose of fast ice sheet drilling.

Wire-Line Drilling

Wire-line drilling is a standard mining and oil industry technology already widely used in cold climates with many relatively inexpensive and standard accessories available for deployment in support of polar research. This technique is currently being used in Antarctica in the Antarctic Geological Drilling (ANDRILL) project. Although this system is limited to ~2.5 km in its current configuration, it may be useful for relatively shallow subglacial aquatic environments. To reach deeper environments, such as Lake Vostok, the maximum drilling depth would have to be increased. In addition, further analysis is necessary to evaluate whether the weight and size of such drills will preclude their deployment with aircraft (LC-130) and prevent moving this system in the field.

Hot-Water Drilling

Hot-water core drilling is another fast drilling technique that can also recover cores. In the past it has been the primary fast access technology in ice-sheet environments mainly to depths <1.5 km (Engelhardt et al., 2000) and is the most established technology for making access boreholes to the bottom of ice sheets. The drill system consists of small hot-water jets contained in an annulus that melts the ice around a core and can be used in conjunction with coreless hot-water drilling. This system has minimal infrastructure and would be quite mobile, which may permit several sites to be sampled in a season. However, in its current configuration, this technique has

3

FASTDRILL: Interdisciplinary Polar Research Based on Fast Ice-Sheet Drilling. Report of an NSF-Sponsored Workshop Held at University of California, Santa Cruz, October 23-25, 2002. A PDF version of the report can be found at http://es.ucsc.edu/%7Etulaczyk/Report_I_V.pdf.



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