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3. State of Current Effort ORGANIZATION Arctic and antarctic field research is funded primarily through the Division of Polar Programs (DPP) of the National Science Foundation (NSF). Proposals from research institutions are evaluated through peer review, and must be compatible with logistical operations organized by DPP. The Polar Ice Coring Office (PICO), located at the University of Nebraska-Lincoln, operates under contract from DPP. It conducts shallow and intermediate depth ice core drilling in Antarctica, Greenland and other high-alpine locations. It is also responsible for providing U.S. logistical support to NSF-sponsored research projects in Greenland. The DPP also supports under contract an ice core storage facility at SUNY, Buffalo, and supports under a research grant a facility for oxygen isotope ratio measurements at the University of Washington, Seattle. Although the main part of NSF support comes through DPP, additional support for ice core research is possible from other NSF sources when specific goals are directed toward the research of these other NSF programs (for instance, Climate Dynamics in the Division of Atmospheric Sciences). Cold regions research is supported by the U.S. Army Corps of Engineers through the Cold Regions Research and Engineering Laboratory (CRREL) at Hanover, New Hampshire. The CRREL was instrumental in the drilling of earlier cores (Camp Century, Greenland, and Byrd Station, Antarctica) but is currently not involved in ice sheet drilling operations. The National Aeronautics and Space Administration supports a limited number of activities related to remote sensing. Polar research is also supported by the Office of Naval Research (ONR), but no ONR funds have been directed toward ice coring. 14
15 Advisory input to DPP/NSF and other agencies may come, upon request, from internal advisory committees and from the National Academy of Sciences/National Research Council (NAS/NRC), through its Polar Research Board (PRB) and Committee on Glaciology. These sources have also provided oversight of specific projects, such as the Greenland Ice Sheet Program (GISP I) and the Ross Ice Shelf Project (RISP). Scientific input also is received from ad hoc panels set up by DPP, such as the Greenland Ice Sheet Program (GISP-II) panel. However, no standing national body of scientists is responsible for planning and executing an integrated long-term ice coring program. International organizations, including the Scientific Committee on Antarctic Research (SCAR), the International Council of Scientific Unions (ICSU), and the International Commission on Snow and Ice (ICSI), are charged with identifying scientific programs of circumpolar scope and significance. International guidance and advice in areas of drilling and core studies in Antarctica was provided to the United States by SCAR and associated groups, particularly by the International Antarctic Glaciology Program (IAGP) for operations in East Antarctica and through a SCAR subcommittee on Ice Core Drilling. The IAGP, composed of scientific and logistic experts from seven countries, has developed a series of international glaciological research programs in Antarctica. An international program for Glaciology of the Antarctic Peninsula (GAP) has also been encouraged (Swithinbank, 1974). All of these bodies have been concerned with ice coring, but no standing international group advises on the scientific and logistical aspects of ice core drilling. ICE CORE DRILLING Ice core drilling began primarily as a U.S. initiative during the International Geophysical Year (IGY). These efforts culminated in the successful penetration to the bed beneath Camp Century, Greenland (1390 m), in 1966 and Byrd Station, West Antarctica (2164 m), in 1968. These successes initiated the growth of research programs in other countries and the modern era of ice core analysis. The early drills were developed at CRREL (a brief history is given in Appendix A). The deep drill used in the 1960s was irretrievably jammed near the base of the West Antarctic Ice Sheet. In the early 1970s, there was an
16 attempt to replace the lost deep drilling capability with a unique wire-line core drill system. However, this was not successful. Subsequent development in the United States of coring technology and hardware for drilling to shallow (less than 50 m) and intermediate depths (less than 300 m) has continued with emphasis on light weight and efficiency. These systems have been used advantageously to expand geographical coverage. Unfortunately, the equipment for reaching greater depths has not been replaced in the United States. The current inventory of U.S. ice drills is detailed in Table 2 of Appendix B. These drills are designed, contructed and operated by PICO at the University of Nebraska. In the last decade, ice drills for all depth ranges have been built in other countries (Holdsworth and others, 1984). At present, drills capable of penetrating ice to depths corresponding to pre-Holocene ice in the interior of big ice sheets exist only in Denmark, France, and the USSR. These drills have been used successfully in Greenland at Dye 3 (Langway and others, 1985b) and in Antarctica at Dome C (Lorius and others, 1979) and Vostok (Lorius and others, 1985). Australia and France are assembling equipment to reach 4000 m depth. These drills include both electrothermal and electromechanical drills, with a variety of design features incorporated in response to the unique requirements of ice drilling. Table 1 of Appendix B details the current international inventory of ice coring systems as it is presently known to the ad hoc panel. Ice drilling is an engineering art confronted by conditions not encountered by the rock drilling technology used in hydrocarbon exploration and extraction (Appendixes A and B). Of principal importance is the close proximity of the ice to its melting point with consequences for ice melt, adhesion and creep. This condition makes it possible to use rather simple thermal corers that penetrate by melting the ice. The meltwater must be removed or mixed with a freezing inhibiting fluid. Accumulated experiences, nevertheless, indicate that mechanical techniques of ice drilling are faster and lighter, require less power, and produce higher quality core. The main problem is efficient removal of ice cuttings, which tend to adhere to each other and drill parts. An important component of ice coring is introduction of fluid into a hole as it is drilled. This provides a
17 pressure balance with the weight of the ice. One purpose is to increase core quality by suppressing fracturing, which is a serious problem in dry hole coring below a few hundred meters depth. Fracturing is fatal for some studies, especially gas measurements. A second purpose is to oppose creep closure of the hole walls. Depending on ice temperature, penetration of a dry hole beyond depths of a few hundred to a maximum of about one-thousand meters is impractical because of rapid closure. The U.S. CRREL developed the first fluid-filled hole drilling technique in 1958-59 at Little America V. Yet, ice core drills in the current U.S. inventory can be used only in dry holes. Although the intermediate-depth drills could easily penetrate deeper, their useful depth range is limited to about 300 m because of the poor quality of cores from below this depth. Similarly, the restriction to dry-hole coring is a barrier to a stepped development of capability for deep coring below 1000 m depth. The advances in other countries have depended on adopting techniques for fluid-filled holes. Although there is a variety of core drills fitting into the shallow, intermediate, and deep descriptions, the proven international inventory does not currently meet all the drilling requirements in Greenland and Antarctica. Without modification, existing core drills cannot penetrate to the greatest depths of the ice sheets (e.g., 3000 m or more) or operate at the coldest temperatures (e.g., - 60Â°C). Also, existing drills and those under construction cannot penetrate sub-ice material effectively. It is probable that all requirements cannot be met in a single drill system. ICE CORE ANALYSIS TECHNIQUES The principal geochemical constituents providing proxy climate information include isotopic composition of the ice (18O/16O and 2H/JH), microparticles (insoluble dust) and soluble impurities (sulfates and other ionic components), heavy metals (Pb, Hg) and enclosed gases (isotopic composition of Â©2, concentrations of CO2, methane, and others), and the isotopic; composition of trace elements ( C, 3C, 10Be, 26A1, 36C1). These constituents also provide means for age dating the ice through identification of annual layering in ice isotopes and impurities, distinct
18 stratigraphic features caused by events dated external to the ice, and the isotopic composition of combinations of trace elements, which change by radioactive decay (Hammer and others, 1978; Herron, 1982a; Oeschger, 1982). Physical and structural measurements on ice cores, including ice texture, rheology, and electrical properties are also important. These are crucial for understanding the flow of the ice sheet and are also related to the geochemistry (Koerner and Fisher, 1979; Herron and others, 1981; Herron and Langway, 1982; Shoji and Langway, 1985). It is particularly important that ice deformation studies be carried out on samples from the crucial region close to the base of the ice. Capabilities for measuring most of these ice core properties exist in the United States. The major activities are microparticle analysis (Ohio State University), ice chemistry, and mechanical and physical property analysis (SUNY, Buffalo), and oxygen isotope analysis (University of Washington). A listing of U.S. institutions with active or strongly interested researchers is given in Appendix C. The principal missing technique in the United States is dry gas extraction needed for measurement of concentrations of trace gases such as CC^. Efficiency and capacity are of major importance. A large number of measurements, exceeding the output of the combined laboratories, may be required for certain parameters. The University of Washington has a capacity of 7000 samples per year for oxygen isotopes. Capacities for hydrogen isotopes are much more limited. The microparticle facility at Ohio State University could measure approximately 15,000 samples per year under full-time active operation. SUNY, Buffalo can do multiple ion analysis at about 8000 samples per year. For comparison, the number of samples needing measurement for a thorough examination of a single deep core is in the range 10,000 to 100,000. Accelerator mass spectrometry (AMS) must play an important role in future ice core research. It is essential for measurement of isotopic composition of the minute amount of trace elements, which are at the forefront of current techniques in ice dating. Measurements can be made at 5 U.S. universities (Appendix C). However, the sample throughput is far below what is required, because four of these facilities only perform part-time AMS research. Laboratory facilities for ice core analysis are more
19 highly developed in Europe. A major organizational difference is that the research efforts are concentrated into a few research institutes, the foremost ones being in Copenhagen, Bern, and Grenoble. The capabilities of these institutes involve all levels of ice core research including drill development, field work including coring and sample preparation, as well as diverse laboratory measurements on the ice, and imaginative interpretation of the results. This coordinated concentration of effort and the positive feedback between capable and committed personnel has resulted in very productive ice core research programs, and the principal innovative techniques in the last decade. With the exceptions of total gas content and CO2 concentration (including C and C isotopes), these European labs do not have a broader spectrum of in-lab measurements than that which is available in the United States. However, the Europeans have been able to achieve a high sample analysis rate (including the new AMS techniques) and sharper focus on interpretations. They have been particularly successful in the development of in-field measurements on cores such as solid conductivity (Hammer, 1980) and bulk particulate concentrations (Hammer, 1977). These are important for optimizing field sampling by providing a tentative time scale and quickly isolating the most interesting sections of core. The United States is behind in this area, although there are some notable successes in field analysis of ion chemistry and mechanical properties (Shoji and Langway, 1985; Herron and Langway, 1985). ICE CORE STORAGE The principal ice core repository in the United States is the Ice Core Storage Facility and Information Exchange of the Department of Geological Sciences at SUNY, Buffalo. Information on this ice core respository is contained in Appendix D. This facility is supported by DPP. The Buffalo ice core storage facility is responsible for the storage, cataloging, and redistribution of ice cores obtained under NSF projects in Greenland, Antarctica, and other regions. Eighty percent of the ice cores in this facility are stored in a commercial freezer facility in the Buffalo area with the remainder stored in SUNY, Buffalo facilities. The NSF/DPP contract under which the facility operates
20 specifies the use and distribution of the ice cores. The Buffalo ice core storage facility is an independent unit that is formally separate from the glaciological research programs at SUNY, Buffalo, although there is an overlap of personnel. Small amounts of core are stored temporarily at other U.S. laboratories where ice core measurements are made. LOGISTICS Ice core drilling in the polar regions requires a strong logistical base for transporting field personnel and supplies, scientific and drilling equipment, fuel and fluid for filling core holes, and the ice core. For deep drilling, the major weights are hole fluid transport to the site and ice core transport from the site. Major deep drilling operations have relied almost entirely on the logistical base provided by the United States and organized through DPP directly in its Polar Operations Section or indirectly under contract to PICO. One exception is the successful coring at Vostok by Soviet research teams. In this case important measurements on Vostok ice in European labs were made possible, in part, by transportation of personnel to the Vostok site by U.S. aircraft. Shallow and intermediate coring does not require so much transport capacity. Some programs of this scale have been conducted with little reliance on U.S. logistics, as for example by the Australians in Wilkes Land. Additional programs independent of U.S. logistics are probable in the future. The general perception at both the national and international levels is that major ice core programs in the future can only be carried out with a major logistical contribution from the United States similar to that provided in the past.