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Laboratory experiments were done to better understand the electrical conduction mechanisms of impure, polycrystalline ice as represented by the 2503 m Dome Fuji (Antarctica) ice core. Also, two electrical measurement techniques for ice cores were compared and their usefulness for determining the acidity of ice cores was studied. We measured the electrical conductivity and complex permittivity of 167 slab-ice samples at frequencies from 20 Hz to 1 MHz. Measurements were performed at –21˚C for all samples, and at –110˚ to –20˚C for several samples, to examine the effects of temperature. We found linear relations between the AC loss factor and the molarity of sulfuric acid, and between the high-frequency-limit conductivity and the AC loss factor. Thus, the acidity levels can be determined from the AC loss factor. In contrast, the electrical conductivity measurement (ECM) current correlated weakly with the other parameters; furthermore, the correlation worsens at larger signal. In several samples containing high acidity, the dielectric properties had distinct changes near –81˚C. We argue that these changes were caused by a change from a liquid-vein-mediated conduction mechanism above the eutectic point of the solute/water/ ice system to a solid-phase conduction mechanism at lower temperatures.

The 320 kyr climatic record from the 2503 m Dome Fuji (Antarctica) ice core was analyzed using two electrical methods: AC-ECM and ECM (electrical conductivity measurements). AC-ECM is a method to detect the complex admittance between electrodes dragged on the ice surface with mm-scale resolution and uses 1V and 1 MHz. the ratio of the real to imaginary part of the admittance is the AC loss factor, which responds linearly to the amount of sulfuric acid and hydrogen ions. Both the AC loss factor and the ECM current respond to acid, but the ECM signal tends to saturate at high acidities. Dome Fuji ice was measured to be highly acidic, with background values of 2–7 μM, and had 4500 major peaks with acidities of up to 90 μM. This ice-core evidence and earlier snow-chemistry survey around the dome region indicates that Dome F may have a better connection to the stratosphere than have sites at lower altitude, which allows more stratospheric aerosol and gases to reach the snow surface. Acidity tends to be high in interglacial periods, but correlation between acidity and δ18O is not straightforward. Electrical signals decreased and smoothed out with increasing depth; the diffusion coefficients deduced from this smoothing were 10–102 times greater than in solid ice. the ice core exhibited electromechanical effects and expelling effects from sulfate peaks.

Air bubbles trapped near the surface of an ice sheet are transformed into air hydrates below a certain depth Their volume and number varies partly with environment and climate. Air bubbles and hydrates at 120-2200 m depth in the Dome Fuji (Dome F) ice core were examined with a microscope. This depth range covers the Holocene/Last Glacial/Last Interglacial/Previous Glacial periods. No air bubbles were seen below about 1100 m depth, and air hydrates began to appear from about 600 m. The observed number of air bubbles and hydrates was similar to that found in the Vostok ice core. For the ice covering the Last Glacial Maximum period, however the hydrate concentration in the Dome F core is about half that of the Vostok core. Reference to snow metamorphism and packing does not explain this finding.

Uniaxial compression tests were performed on samples of the Greenland Ice Gore Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate (type A) and constant load (type B). Fifty-four uniaxial-compression test specimens from 1327-2922 m were selected. Each test specimen (25 mm x 25 mm x 90 mm) was prepared with its uniaxial stress axis inclined 45° from the core axis in order to examine the flow behavior of strong single-maximum ice-core samples with basal planes parallel to the horizontal plane of the ice sheet. The ice-flow enhancement factors show a gradual increase with depth down to approximately 2000 m. These results can be interpreted in terms of an increase in the fourth-order Schmid factor. Below 2000 m depth, the flow-enhancement factor increases to about 20-30 with a relatively high variability When the Schmid factor was > 0.46, the enhancement factor obtained was higher than expected from the .-axis concentrations measured. The higher values of flow-enhancement factor were obtained from specimens with a cloudy band structure. It was revealed that cloudy bands affect ice-deformation processes, but the details remain unclear.

An X-ray transmission method has been developed to obtain a continuous profile of bulk densities of ice cores. Intensities of X-rays transmitted through an ice-core sample were continuously measured by an X-ray detector during translation of the sample across the X-ray beam. A thick section of an ice core with a constant thickness was prepared by band-sawing followed by microtome planing. The X-ray intensity profile obtained was converted to a density profile using a calibration curve for X-ray absorption vs ice thickness. Using this method, spatial resolution of the density profile was down to 1 mm. X-ray radiographs were also taken on a two-dimensional detector imaging plate, in order to observe layer structures of the ice cores.The method was applied to Dome Fuji (Antarctica) ice cores from the surface to 110 m depth. From the density profile obtained we calculated the power spectrum of the density variation by the discrete Fourier transform, and obtained several peaks at different frequencies. The center period in the spectrum was close to the annual accumulation thickness at the drill site.

A comprehensive study of ice-crystal fabrics and textures was conducted on the Dome F (Antarctica) ice core. Crystal ,-axis orientations, crystal sizes and crystal shape were measured on thin sections with an automatic ice-fabric analyzer. The general feature of textural and fabric development through a 2500 m long core was obtained by a 20 m interval study. Crystal size steadily increases with depth except for depths of about 500,1800, 2000, 2200 and 2300 m, at which depths crystal size decreases suddenly. There is a clear correlation between crystal-size and ´18O values. Crystals tend to elongate horizontally with depth, and the aspect ratio (long axis vs short axis of a grain) increases twofold at 1600 m depth and fluctuates below that depth. The .-axis orientation fabrics gradually change with depth from a random orientation pattern near the surface to a strong vertical single maximum at 2500 m. These are very similar to those from the GRIP (Greenland) core The observations of crystal shape and the fabric measurements indicate that nucleation-recrystallization does not take place at Dome F.

An ice core to 2503.52 m depth was drilled during 1995 and 1996 at 77°19′01″S, 39°42′12″ E (3810 m a.s.l.), at the summit of Dome Fuji, East Antarctica. Climatic and environmental conditions were observed at the coring site throughout the 2 years of wintering operation. Meteorological and glaciological observations made clear the present surface processes of mass balance. The chemistry of the surface snow layers was observed for investigation of the atmospheric environment reflected in snow deposits. Core analyses have been carried out in Japan. Permeability and density measurements show that air bubbles are completely closed off by densification processes at about 98 m depth. The vertical profile of δ 18O suggests that the core covers two warm stages and one cold stage from the surface down to 1800 m depth. The transition from the cold to the warm period affects the vertical distribution of ice-crystal size. The chemical constituents in the ice core show large differences between warm and cold periods. A depth–age relationship is presented and a study made of palaeoclimatic and core signals.

Horizontal and vertical distributions of melt features (ice layers) were examined using two ice cores (206.6 and 101.5 m deep, 1 m apart) from Site J (66°51.9′ N, 46°15.9′W, 2030 m a.s.l.). The temperature at 10 m was −16.3°C. We observed 2804 melt features, with a total thickness of 30.32 m, in the 206.6 m core, corresponding to 16.4% by volume of the ice-equivalent core length. Horizontal distribution of melt features was examined by correlating melt-feature thicknesses in the two cores. The correlation coefficient was 0.71 (n = 514) for each melt feature in the two cores. It was maximum for data passed through 5 and 40 year low-pass filters. A significant relationship (P = 0.005, n = 36) was obtained for the vertical distribution of melt features and the June temperature on the west coast of Greenland (Jakobshavn). Using this, June temperatures at Jakobshavn since 1550 were estimated. There are three periods (1685-1705, 1835-70 and 1933-45) during which mean June temperatures clearly decreased, when they were estimated to he 0.1°, 0.4° and 0.2°C lower than the average for the whole period (1550-1989). The first two “cold” periods have been identified in melt features of the Dye 3 and Devon Island ice cores and in a tree-ring profile from Yukon Territory, Canada. Melt-feature percentages in the Site J ice core have increased since about 1945, probably reflecting summer-temperature warming on the ice sheet.

Snow blocks were slid down natural snow slopes and filmed with a video camera. Friction coefficients were calculated from time-distance curves and the equation of motion. Dry-friction coefficients ranged from 0.57 to 0.84, and could be separated into Coulomb friction and a friction component proportional to the contact area of the blocks (adhesion). These values are greater than the values usually used in avalanche dynamics, but are consistent with previous coefficients obtained for snow blocks sliding over snow. When uniform ploughing occurred and a shear layer developed along the track the apparent friction coefficients increased with velocity, and could be modelled by considering the kinematic viscosity of the snow. The values of kinematic viscosity ranged from 10−3 to 10−4 m2/s and agreed well with those values obtained by other researchers.

Observations and measurements were made of high-speed avalanches at Shiai-dani, the Kurobe canyon, to reveal their real features and properties, using strain-gauge-type load cells in measuring impact force and speed. A maximum impact pressure of 140 × 104 N m-2 was obtained, as well as data indicating the existence of a number of wave fronts, ranging in speed from 9 to 60 m s -1 inside an avalanche. Violent changes in atmospheric pressure ranging from -21 to +5 mbar were observed near its path when a high-speed avalanche passed by.

Preliminary results of the analyses on 700 m ice cores retrieved from Mizuho Station, Antarctica, in 1983 and 1984 are presented. The majority of the physical properties, density, grain-size and shape, and total gas content, were measured at the drilling site. Fabrics, microparticle concentration, electrical conductivity, and stable-isotope concentration δ18O were measured in laboratories after the cores had been taken to Japan. In spite of inaccuracy in measuring both density and total gas content in the ice, due to interlocking cracks in cores, several attempts were made to correct the data. The coincidence between the incremental peaks in the depth profile of the microparticle concentration, as well as in the electrical conductivity and the warm trend indicated by the δ18O profile is discussed. The shape of the δ18O profile is characterized by two inflection points and is compared with results obtained from the Byrd Station, Dome C and Vostok cores. From this comparison, it is tentatively concluded that the bottom of the Mizuho core may be an age of the order of 10 ka B.P.

The internal structure of powder-snow avalanches was investigated at Kurobe Canyon in the Shiai-dani area of Japan in 1988. Internal velocity was derived for avalanches of this kind by frequency analysis of impact-force data, and was found to undergo a remarkable change with time. The shear of the avalanche flow was estimated to range from 1 to 7 s−1. The front region of the avalanche wind was observed to precede the front of the avalanche by a distance of 17.3 m. The maximum wind velocity was comparable with the internal velocity of the front region of the avalanche.

Between May 1983 and July 1984 glaciological parties of the 24th and 25th Japanese Antarctic Research Expeditions (JARE–24 and 25) carried out ice-core drilling using a thermal drill, down to 700.5 m depth at Mizuho Station (70°41'53"S, 44°19'54"E), as a part of the Glaciological Research Program in east Dronning Maud Land, Antarctica. The thermal drill, 3.9 m long and capable of taking a core 1.5 m long and 130 mm in diameter, is an improved version of a drill used by JARE–15 in 1975. The most important improvement was the monitoring system during drilling, for which a micro-computer was fitted in the drill. By using this system, such accidents as heater burn-out, tank overflow and failure of water suction would immediately be brought to our attention. The drilling speed was about 1.6 m/h, when the optimum output was 3.6 kW. The core recovery rate was above 99%. The core quality was good down to a depth of 80 m. Between 80 and 120 m, cracks were found at intervals of 0.15–0.5 m, and horizontal cracks were found continuously at intervals of 0.01 m or less. Immediately after the core was pulled, the stratigraphy was observed and bulk density was measured. A dust band, presumably volcanic particles, was seen at only 500.2 m depth during stratigraphic observation. The following analyses were carried out at Mizuho Station within a month of recovery: (1) Density determination by the hydrostatic method. (2) Measurement of total gas content. (3) Thin-section analyses, including observation of cracking around air bubbles and the crystalline texture, and ice-fabric studies. The 700.5 m core has been brought to Japan, and the following analyses are now under way: (1) Oxygen-isotope ratio. (2) Concentration of microparticles. (3) Electric conductivity. (4) Chemistry of soluble impurities.