Exploration of Antarctic Subglacial Aquatic Environments Environmental and Scientific Stewardship (2007) / Chapter Skim
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4 Drilling and Sampling Technologies and the Potential for Contamination
4 Drilling and Sampling Technologies and the Potential for Contamination
Pages 81-103
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From page 81... ...
Fast access ice sheet drilling generally proceeds without the recovery of a continuous ice core, and, in most cases, is used to reach scientific targets deep within or below the ice surface. This approach may be useful for the exploration of subglacial aquatic environments if drilling platforms such as (1)
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From page 82... ...
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.
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From page 83... ...
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.
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From page 84... ...
Hybrid Systems It appears that at the present time no single technology exists that provides a means to access subglacial aquatic environments in a clean manner. It may be possible, however, to combine different drilling technologies to reach this goal.
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From page 85... ...
Another approach to reach subglacial aquatic environments is to use conventional electromechanical ice core drilling techniques to reach an environmentally safe depth above the top of a lake. This safe distance would preclude the possibility that microfractures in the ice would allow the borehole fluid to migrate along an intergranular vein network and enter the lake.
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From page 86... ...
It is conceivable that at least some of the subglacial aquatic environments may be substantially overpressure. Further technological developments, such as introducing pressure-tight locks in the bottom parts of a borehole may eventually be advisable to deal with this possibility as well as to sample subglacial lake bottom sediments.
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From page 87... ...
encouraged the subglacial research community (through NSF) to draw on the expertise in the ocean science community to overcome these challenges and said that NSF should encourage the development of new and creative approaches to the exploration of subglacial aquatic environments.
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From page 88... ...
Are there new techniques to assemble a sensing system within the ice or within the lake? The future technology workshop participants found that another impediment to the planning and design of technologies for subglacial exploration is the lack of knowledge about the aquatic environments (e.g., how corrosive is the water?
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From page 89... ...
. Other drilling fluids include n-butyl acetate, as used at the Dome Fuji site in Antarctica and on the Greenland ice sheet at the GISP2 borehole (Table 4.2)
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From page 90... ...
Talos Dome, Antarctica PNRA 2005 - WAIS Divide NSF OPP NOTES: AARI = Arctic and Antarctic Research Institute; AWI = Alfred Wegener Institute; BAS = British Antarctic Survey; CRREL = Cold Regions Research and Engineering Laboratory; GRIP = Greenland Ice Core Project; IPEV = French Polar Institute; NIPR = National Institute of Polar Research; OPP = Office of Polar Programs; PNRA = National Research Program in Antarctica.
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From page 91... ...
DRILLING AND SAMPLING TECHNOLOGIES AND POTENTIAL CONTAMINATION Depth (m) Fluid Notes 1391 Aqueous ethylene glycol solution; Fuel DF-A + trichlorethylene 2164 Aqueous ethylene glycol solution; Drill was stuck in the year during Fuel DF-A + trichlorethylene resumption of the drilling 812 Aqueous ethanol solution Hole was plugged by ice chips 2037 Fuel Jet A-1 + perchlorethylene Drill was stuck 2202 Fuel TS-1 + CFC 11 Drill was stuck 2546 Fuel TS-1 + CFC 11 Drill was stuck 3029 Solvent D60 + CFC 113 3053 n-butyl acetate Kevlar cable was damaged 1196 Fuel Jet A-1 + perchlorethylene 554 n-butyl acetate 1371 Solvent D60 + HCFC 123 The drill was stuck, not recovered Shell Exxol D60 + HCFC 141b 3086 Shell Exxol D60 + HCFC 141b Subglacial water rose in borehole at Small amounts of aqueous ethanol completion solution in deepest 100 m 2500 n-butyl acetate The drill was stuck, not recovered 3623 Fuel TS-1 + CFC 11; Fuel TS-1 + HCFC 141b 1003 n-butyl acetate 723 Fuel TS-1 + HCFC 141b 3270 Shell Exxol D60 + HCFC 141b First drill stuck in 781 m, not recovered Insignificant amount of aqueous ethanol water solution 2774 Shell Exxol D40 + HCFC 141b Subglacial water rose in borehole at Insignificant amount of aqueous ethanol completion approx.
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From page 92... ...
C., 2005a, Glacial 4.01 ice cores: a model system for developing extraterrestrial decontamination protocols, Icarus 174:572-584. Copyright (2005)
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From page 93... ...
Since many of the subglacial aquatic environments are likely to contain a low biomass of microbes it is of critical importance to minimize the introduction of exogenous microbes, whether living or dead, and even of exogenous nucleic acids to (1) prevent changes in the native microbial composition and (2)
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From page 94... ...
Spores that might be either introduced to or removed from subglacial aquatic environments represent a potentially different situation because they are able to survive under many extreme conditions over very long time frames (millions of years) (Vreeland et al.
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From page 95... ...
liquid-water conditions of a subglacial lake could result in a short-term phase of increased metabolism and growth. A variety of hydrodynamic circulation processes are likely to operate in Lake Vostok and other subglacial waters, and localized inputs of contamination could be widely dispersed, including between lakes via subglacial hydrological networks.
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From page 96... ...
In terrestrial settings, rotary drilling is a common method when drilling to depths >100 m, although cable tool drilling has also been used to obtain high-quality samples for microbial analysis from unconsolidated sediments from at least 200 m and has the advantage that no recirculating drill fluids are necessary. Push-type core barrels such as split-spoon core barrel devices are the most common samplers used in cable drilling to obtain core samples of formation materials for microbiological
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From page 97... ...
, operating from 2003 to the present (built from the successful legacy programs, the Deep Sea Drilling Program [DSDP] and the Ocean Drilling Program [ODP]
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From page 98... ...
Intrusion of fluorescent microspheres into the core interior was not detected in the APC-cored unconsolidated sediments or RBC-cored consolidated sediment or rock. However, microspheres were detected in thin sections tested from the igneous rock samples, leading researchers to conclude that processing of the rock after sample extraction was the likely source of contamination (Smith et al.
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From page 99... ...
DRILLING AND SAMPLING TECHNOLOGIES AND POTENTIAL CONTAMINATION include Class 100K (International Organization for Standarization [ISO] Class 8)
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From page 100... ...
. These methods use epifluorescence microscopy or flow cytometry to quantify the fluorescent-stained cells, and they are appropriate to the ongoing analysis of Antarctic glacial ice and drilling fluids for environmental monitoring and management.
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From page 101... ...
Current drilling technologies are not sterile and it is not possible to guarantee that subglacial aquatic environments will not be contaminated during drilling, sampling, and monitoring. Drilling approaches that result in freezing subglacial water inside the borehole have worked well to keep the drilling fluids in the borehole (Byrd and EPICA DML boreholes in Antarctica and the NGRIP borehole in Greenland)
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From page 102... ...
could be introduced into subglacial aquatic environments from microorganisms native to the surface environment or from humans or equipment brought to the sampling area. Microbes could be transferred deeper into the system through sampling and could potentially grow (e.g., in meltwaters produced during hot-water drilling)
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From page 103... ...
Drilling and sampling equipment can be cleaned prior to entering the ice, but the extreme depths achieved during drilling and the fact that the drilling hardware is inaccessible for subsequent cleaning make stringent bacterial cleanliness requirements such as those implemented in space research unrealistic. The hydrodynamic nature of subglacial aquatic environments facilitates cell transfer from any object that may find its way into liquid water.
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