Search

The Japanese second deep ice coring project was carried out at Dome Fuji, Antarctica. Following the drilling of the pilot hole in 2001, deep ice core drilling led by the Japanese Antarctic Research Expedition (JARE) was conducted over four austral summer seasons, beginning with the 2003/04 season and reached a depth of 3035.22 m near the bedrock in January 2007. The new drill was designed and developed with the goals of (1) solving the problems encountered during the first JARE deep coring drill and (2) achieving more efficient drilling. In particular, the maximum core length that can be drilled at one time was increased from 2.30 m to 3.84 m and the chip storage efficiency was enhanced by a special pipe with many small holes. This paper gives an outline of the improved drilling system, the progress of drilling and various drilling data.

The second deep ice coring project was carried out at Dome Fuji, Antarctica. Following the pilot hole drilling in 2001, deep ice core drilling was conducted for four years from the 2003/2004 austral summer season, reaching a depth of 3035.22 m in January 2007. The drilling was performed only in the summer season. Therefore, many improvements were made to the problems of the first deep ice core drilling system to enable efficient drilling. In particular, the core length that can be obtained at one time was increased from 2.3m to 3.84 m, and the chip storage efficiency was enhanced. In this report, the outline of the drilling system, the method of drilling, the progress of drilling operation, and various troubles were reported. Also, future issues are indicated.

We investigated the effects of microparticles and grain size on the microstructural evolutions and mechanical properties of polycrystalline ice. Uniaxial compression tests were conducted using fine-grained pure ice and silica-dispersed ice under various conditions. Deformation behavior of fine-grained ice was found to be characterized by stress exponent n ≈ 2 and activation energy Q ≈ 60 kJ mol−1. The derived strain rates of fine-grained ice were ≈ 1 order of magnitude larger than those of coarse-grained ice obtained in previous studies, and they were found to be independent of particle dispersion and dependent on the mean grain size of ice, with grain size exponent p ≈ 1.4. Work hardening was observed in dislocation creep, while the strain rate continued to decrease. These results indicate that the deformation mechanism of fine-grained ice is different from typical dislocation creep, often associated with n = 3. Although microparticles restricted grain growth, there was little direct effect on the deformation of fine-grained ice. Microstructural observations of the ice samples indicated that the grain boundaries were straight and that the subgrain boundary densities increased after deformation. Our experiments suggest that grain size and boundaries play important roles in the deformation processes of polycrystalline ice.

Deep ice coring to bedrock (3028m in depth) at Dome Fuji Station is planned during three successive summer seasons starting from 2003/2004. An improved JARE deep ice core drill (12.2m in length and 3.8m in maximum core length) was developed in December 2001 for the ice coring at Dome Fuji. In January/February of 2002,we performed experiments on drill performance using artificial ice blocks in Rikubetsu, Hokkaido. In this paper, we outline the experiment and report the results. It was found through the experiment that an ice core of 3.8m length was smoothly obtained by the improved drill with three screws in the chip chamber and cutting pitch of 5mm/cycle. About 45000 small holes 1.2mm in diameter were made on the surface of the chip chamber. These small holes enabled liquid to circulate between cutters and outside of the drill through the chip chamber in the drill. The dry density of the chips was 440 to 500kg/m^3 and the chip recovery rate during ice coring was 65 to 91%. A check valve installed at the bottom of the chip chamber to prevent outflow of chips from the drill was not tested enough, but more durability is needed for the valve. The newly developed motor system and core catchers of the drill worked perfectly. The average coring speed was 24.5cm/min with cutting pitch of 5mm/cycle. The average power consumption during ice coring was 171W.

Deep ice coring was carried out at Dome Fuji Station, Antarctica in 1995 and 1996 following a pilot borehole drilled and cased with FRP pipes in 1993,and reached 2503.52m in December 1996. Total numbers of ice coring runs below the pilot borehole and chip collection were 1369 and 837 respectively. The mean coring depths per run and per day were 1.75m and 8.21m respectively. We report the outline of the coring operation, the system, coring method, and troubles encountered during the coring work.

In the area west of Mizuho Plateau, outflow of the ice sheet is hindered by a chain of mountains (Sor Rondane, Belgica and Yamato Mountains etc.) lying along the coast of the continent and ice shelves are developing at the margin of the ice sheet. Therefore the ice sheet geomorphology and dynamical behavior in this area are quite different from those on the Mizuho Plateau. In order to describe the response of the East Antarctic ice sheet to climatic change, we need to know the influence of the presence of mountains on stability of the ice sheet. This glaciological study aims to investigate whether the ice sheet and the ice shelf in this area are now increasing or decreasing in size possibly, in response to atmospheric warming, how far this part of the ice sheet departs from a steady state, and how the influence of climatic change is left inside the ice sheet and the ice shelf. For this purpose the following studies were performed in 1988 and 1989. 1) A series of shallow drillings along a selected flow line upstream of the Sor Rondane Mountains to Breid Bay. 2) Surface flow velocity, strain and mass balance measurements on the flow line. 3) Monitoring of a valley glacier in the Sor Rondane Mountains.

A deep ice coring system for Dome Fuji project has been developed under a project coordinated by the National Institute of Polar Research. Three reports have been issued already, mainly about the development of the drill system. We report here on the drilling site and equipment such as winch, drilling cable, mast, control panels, chip caching tools (filter) and so on as well as the drill. This paper includes an outline of drilling site and work, progress of machine design and final specifications of the above equipment.

A deep ice coring system, which is to be used at Dome Fuji Station located at the summit of the Queen Maud Land ice sheet in 1995 and 1996,has been under development since 1988. The mechanical system was designed to reduce power consumption and weight. Many experiments were carried out on parts of the system in a cold laboratory. Simultaneously, field experiments of the drill system were done at Dome GRIP, Greenland ice sheet and at Rikubetsu, Hokkaido. As a result, a electro-mechanical drill which is simple both in shape and mechanism can be designed and produced incorporating many new ideas introduced through the experiments.

Recent observations show that the ice sheet in the Shirase Glacier drainage basin, East Antarctica, is thinning. If the observed thinning is assumed to be a transitional process in which the ice sheet is adjusting to the present climate, an equilibrium ice sheet profile which adjusts to the present climate would provide us with information for understanding the present behavior of the ice sheet. The equilibrium ice sheet profile was estimated by using a three-dimensional non-steady state ice sheet model. Estimations were carried out with data based on observations of bedrock topography, surface elevation, accumulation rate and surface temperatures, and their extrapolation for areas where there is no field data. And the equilibrium ice sheet profile against various parameters, e.g. surface temperatures, accumulation rate and geothermal heat flux, was investigated. Results of the calculation showed that an almost stationary state of the ice sheet was achieved after (10)^4 model years when started from the present profile of the ice sheet. The equilibrium ice sheet profile depended on bedrock topography and tested parameters sensitively, but the calculations indicated that ice-thickness tend to decrease in the middle-stream region in general. It was also revealed that the ice sheet in the vicinity of the Yamato Mountains was relatively stable even if the parameters were changed.

A deep ice coring system, which is to be used a top the Queen Maud Land ice sheet in 1994-1995 with a plan named "Dome Project", has been developed since 1988. A mechanical system was adopted because of its less power consumption and smaller size compared with a thermal system. Experiments were done for mechanisms of ice cutting, chip transportation, chip storage, antitorque, monitoring sensors, and winch control with a 20-m drill experiment tower. Experiments were also done in Antarctica. This is an interim report of the development of the JARE deep ice coring system.

Summer party of the 31st Japanese Antarctic Research Expedition (JARE-31) carried out maintenance of automatic meteorological stations, glaciological observation, and drilling test for "Antarctic Climate Research (ACR)" Project from late December 1989 to January 1990 around the Sφr Rondane Mountains region. This party is constituted by four glaciologists including two Belgian observers and one JARE-30 member. Three prototypes of electromechanical ice drill for deep core sampling using untifreezing liquid were successfully tested on a bare glacier at Jenningsbreen (Jennings glacier). On the same glacier, dynamics of glacier movement were studied by Belgian observers. Mass balance measurement was conducted on Goosen-breen (Goosen glacier) of Brattnipene. Two helicopters were employed for geological and topographical survey in the Sφr Rondane region, so that we were able to fly to Nansenisen, south of Sφr Rondane, and to obtain surface bare ice within dust band (volcanic ash?).