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52 Mellor and Sellman, 1976). The temperature of the ice (temperate or cold) is an additional constraint on the equipment and techniques that can be used. Ice core drills and techniques may be further classified by depth. For this purpose the depth interval 0-50 m is designated as shallow or manual core drilling, the interval 0-300 m (dry hole) as intermediate, and beyond 300 m and requiring a liquid-loaded hole as deep drilling. Shallow and intermediate coring capabilities exist today in several countries including Australia, Canada, Denmark, France, Japan, Soviet Union, Switzerland, United States and the Federal Republic of Germany (Table 1). Of these countries, the United States probably has the largest drill inventory, and virtually all of these drills are fabricated, maintained, and operated by the Polar Ice Coring Office (PICO) at the University of Nebraska-Lincoln (UN-L) under contract to the National Science Foundation's Division of Polar Programs (NSF-DPP) (Table 2). Ice core drilling in the United States has focused in recent years on dry hole drilling to shallow and intermediate depths. In the U.S. inventory there are three kinds of drills used to obtain cores to various depths depending on ice temperature and strain history. First, the manually-operated coring auger is capable of drilling to 50-m depth, which allows scientists to obtain core for preliminary evaluation without calling for a full-scale drilling operation. The SIPRE coring auger and the PICO lightweight auger (Koci, 1984) are also currently in use. Second, the electromechanical drill employs the principles of the hand auger but extends the capability to the 300 m range where core quality generally deteriorates because of stresses within the ice. The drill is raised and lowered by means of an electromechanical cable, which also transmits power to drive the drill. In the U.S. inventory, the PICO 4-inch drill and 200-m winch provide the intermediate-depth drilling capability. In principle, this type of drill has unlimited capability if adapted to drill in a fluid-loaded hole. Third, thermal core drilling has been done successfully in ice over the temperature range of 0° to -55°C to depths of over 2000 m in a fluid-filled hole and to 990 m in an open hole. The current PICO thermal drill was designed for use in ice warmer than -10°C.

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53 TABLE 1. Current International Ice Core Drilling Capabilities Drill Type Country Electro- mechanical Electro- Max. Depth Diameter thermal (m) (mm) Australia X 385 118 Canada X 270 98 Denmark X X 2038 200 102 75 France X ? 115 Japan X 143 X 148 105 105 Soviet Union X 2000+ 110 Switzerland X 300 75? West Germany X 100 75

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54 TABLE 2 Current U.S. Ice Drill Capabilities of Equipment Maintained by PICO for the National Science Foundation A. Downhole Components Drill Title Depth Core Otv. Tvpe Capability (m) Diameter (cm) PICO Lightweight Auger 20-m System A 2 50-m System B 5 Manual Coring Auger 50 7.6 10.0 15.0 NSF-Swiss Drill 1 Electromechanical 115 7.6 PICO 4-Inch Drill 6 Electromechanical 353 10.0 500 l PICO Thermal Drill 1 Electrothermal 312 40002 8.7 PICO Hot Water Drill 1 Hot H2O 220 30.0 Hole 5002 Temperature Logger 1 Logging Instrument Dry Hole Any Size 300 Borehole Borehole Instrumen- 1 Logging Instrument No 20.0 Maximum tation Package Limit Borehole Diameter B. Winches Winch Title Otv. Drills Applicable to Winch Depth Capability PICO 100-m Winch 1 NSF-Swiss 100-m Winch 2 PICO 200-m Winch 7 PICO 500-m Winch 1 NSF-Swiss Drill 200 PICO 4-Inch Drill NSF-Swiss Drill 100 PICO 4-Inch Drill 300 NSF-Swiss Drill PICO Thermal Drill PICO Hot Water Drill 500 Depth capability is dependent on ice temperature and strain history: usual limit is core quality or hole closure. Untested to specified depth

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55 The PICO thermal drill was used to collect cores to bedrock (168 m and 154 m) on the tropical Quelccaya Ice Cap, Peru, in 1982 (Koci, 1983). Any of these U.S. shallow and intermediate drills currently in the PICO inventory can be used in remote areas of the world and are capable of being backpacked, if required. In the development and use of deep ice core drill technology, the United States was the undisputed leader in the mid-1960s with the success of the Electrodrill in obtaining a deep core to 1390 m through ice and into sub-ice material at Camp Century (Ueda and Garfield, 1968) and to 2164 m at Byrd Station (Ueda and Garfield, 1969). After the loss of the Electrodrill in 1968-69, there was no decision made to replace the drill. A unique wireline core-drilling system was designed and contructed at CRREL to drill ice core and access holes for the Ross Ice Shelf Project (Hansen, 1976; Rand, 1977). The wireline system, utilizing components and techniques from the diamond core drilling and rotary drilling industries, provides the capabilities of directional drilling and sampling sub-ice material. Test of the wireline system conducted in Greenland during 1975 and on the Ross Ice Shelf during 1976-77 and 1977-78 demonstrated the effectiveness of lightweight composite drill pipe and both air and fluid circulation systems to remove cuttings. Today, deep drills exist or are under development in Australia, Denmark, France, and the Soviet Union. The Danish deep drill (Gundestrup and others, 1984), which penetrated to a depth of 2037 m at Dye 3, has proven its ability to drill deep in ice; however, it appears that cutter design, motor torque, and drill torque restraint are not adequate for drilling in sub-ice material. There is also some question as to whether the electronics component will continue to function in deeper and colder ice. Further development and testing would be required to determine its capabilities. The Australian deep drill, currently under development, is fashioned after the Danish drill. The French electromechanical drill is still being developed. Their major problem with this drill has been excessive power consumption in the fluid-circulation/ chip-collection system. It is doubtful that the French will have the ability to recover deep sub-ice cores in the near future. Their present and future deep coring efforts concentrate mainly on thermal techniques. The French thermal drill which was used to collect core to

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56 905 m at Dome C, Antarctica, in 1977-78 was used in an open hole. They are now modifying this to penetrate to 4000 m. The Soviet Union has also concentrated mainly on developing deep thermal coring devices. Their thermal drills operating at Vostok Station, Antarctica, are approaching the deep ice coring record set by the United States in 1968 at Byrd Station. The Electrodrill is the only deep drill capable of coring, and which did core, into sub-ice material. The Soviets are reportedly developing an electromechanical drill that may eventually have this capability. TECHNOLOGICAL CHALLENGES Recent technological development and core drilling successes in the U.S. program of shallow and intermediate coring have led to the call for quality ice core from greater depths in both temperate and cold ice in polar, mid- and low-latitude regions. The next logical step in U.S. drill development would be to enhance core quality and to extend the depth capability beyond the 200 m range. Both of these goals can be accomplished by adapting existing intermediate-depth coring drills to work in a fluid-loaded hole. The ultimate long-range goal would be the development of a deep drill capable of operating in ice at -55°C to 4000 m depth with added capability of coring into sub-ice material. Many of the technological challenges associated with development of a U.S. deep drill are already being addressed. Materials that will work in ice at -55° have been tested at the South Pole with favorable results. Several alloys are available that meet the hardness and toughness requirements for cutters and core catchers. Cutter geometry is being defined, which will allow the generation of coarse chips that can be easily pumped and filtered within the drill. Techniques for pumping and filtering slurries are being investigated. Laboratory tests of these components using a modified PICO 4-inch drill will be useful in determining the final configuration of a deep drill. Investigators involved in analysis of the physical and chemical properties of ice have as a primary concern the collection of good quality, unfractured core. Fluid contamination of the core surface is not a major concern

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57 for most investigators except for those working on trace metals and for all others in instances where the core is severely fractured. Increasing the core diameter from the current 10 cm to 15 cm will provide more robust core and larger samples, while making the design task easier. A parallel program emphasizing lightweight drill components and alternate energy sources is also justified. The value of collecting core from high altitude remote locations on a worldwide basis was demonstrated in 1983 with the collection and analysis of two ice cores to bedrock on the Quelccaya Ice Cap, Peru. A PICO 200 m winch, thermal drill, and 2-kW solar array were used to collect the cores. Additional lightening measures are in order, but the downhole and winch components of the drill remain intact. Significantly lighter and less expensive solar panels will be available in the near future. Additionally, hot water drills and instrumentation for gaining access to the glacier bottom are currently available with a practical depth limit of 1000 m based solely on system size. This system could be designed to take core at intervals if necessary. A STEPPED PROGRAM FOR DRILL DEVELOPMENT We recommend an integrated approach to ice core drilling and drill development in the United States The equipment and techniques for reliably drilling shallow and intermediate depth cores already exists in the U.S. inventory. These drills should continue to be used while efforts are being made to meet the larger objectives of deep core drilling. Many opportunities exist in the worldwide glaciology program in the polar regions, tropics, and temperate glaciers of North America and Eurasia that could take full advantage of the existing capabilities while awaiting the development of a deep drill. The first phase in the development of a U.S. deep drill system would be to expand the capability of the existing intermediate drill to enable it to work in a fluid-loaded hole to depths in the 1000 m range. This could be accomplished by using existing surface components (winch, cable, generator), and modifying and instrumenting the downhole components of the PICO intermediate drill. The capability should be sufficient to ensure the collection of core samples that predate the

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58 Wisconsin-Holocene boundary at the South Pole, the Little Ice Age at Siple Station and on the Antarctic Peninsula, and reach to 2000-3000 years B.P. in central Greenland. The second phase would be to extend the depth capability to the 4000 m range, develop the capability of coring into sub-ice material, and improve the borehole logging instrumentation package. Cooperation among core users and drilling engineers on a national and international basis is essential to ensure the successful and timely development of deep ice core drilling capability in the United States and the provision of core samples and other data that best benefit the scientific community. REFERENCES Gundestrup, N. S., S. J. Johnsen, and N. Reeh. 1984. ISTUK: a deep ice core drill system. Pp. 7-19 in ^ Ice drilling technology, G. Holdsworth and others, eds. U.S. Army CRREL Special Report 84-34. Hansen, B. L., 1976. Deep core drilling in the East Antarctic Ice Sheet: a prospectus. In Ice-Core ^ Drilling, J. Splettstoesser, ed., Univ. of Nebraska Press, pp 29-36. Hansen, B. L. 1984. An overview of ice drill technology. Pp. 1-6 in Ice Drilling Technology, G. Holdsworth and others, eds. U.S. Army CRREL Special Report 84-34:1-6. Holdsworth, G., K. C. Kuivinen, and J.H. Rand, eds. 1984. Ice drilling technology. U.S. Army CRREL Special Report 84-34. Koci, B. R. and K. C. Kuivinen 1984. Instruments and methods: the PICO lightweight coring auger. Glaciol. 30(105):244-245. Koci, B. R. 1984. Instruments and Methods: Ice core drilling at 5700 mpowered by a solar voltaic array. J. Glaciol. 30(105):244-245.

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59 Mellor, M., and P. V. Sellmann. 1976. General considerations for drill system design. Pp. 77-111 in Ice-Core Drilling, J. Splettstoesser, ed. Lincoln, Nebraska: University of Nebraska Press. Rand, J. 1977. Ross Ice Shelf Project drilling, October-December 1976. Antarct. J. U.S. XII(4):150-152. Splettstoesser, J. F., ed. 1976. Ice-Core Drilling. Lincoln.Nebraska: University of Nebraska Press. Ueda, H. T., and D. E. Garfield. 1968. Drilling through the Greenland Ice Sheet. U.S. Army CRREL Special Report 126. Ueda, H. T., and D. E. Garfield. 1969. Core drilling through the Antarctic Ice Sheet. U.S. Army CRREL Special Report 231.