ABSTRACT. Biaxial compression tests on glacier ice with bubbles revealed that elongated air bubbles were d eveloped with long axes in the direction of free expansion. The elongated bubbles were not only derived from spherical bubbles but also created by the h ealing of cracks that were developed during compression. Formation of elongated bubbles and foliations in natural glacier ice are discussed h ere in the light of results obtained experimentally. RESUME. Experiences preliminaires sur la formation tU bulles de l' air allongees dalls la glace de glacier sous contrainte. Des essais de compression biaxiale sur la glace de glacier contenant des bulles m ontrent que des bulles de l'air a llongees se developpent avec l'axe long dans le sens de l'expansion libre. Les bulles allongees ne se forment pas seulement a partir de bulles spheriques, mais aussi par l'inclusion de fissures form ees au cours de la compression. L es auteurs discute de la formati on des bulles allongees et de la foliation da ns la glace de glacier naturelle a la lumiere des resultats obtenus experimentalement. ZUSAMMENFASSUNG. Vorliiufige Versuche zur Bildung ver/angerter Luftblasen in Gletschereis durch
Measurements of density, total gas content, δ18O, and electrical conductivity were carried out along a core 100 m long. A profile of in-situ bubble pressure was obtained from the data on density and total gas content, taking into account the volume relaxation of the core in the period between core recovery and density determination. The bubble pressure was appreciably higher than the overburden pressure at corresponding depths. It was considered that the pressure difference was caused by the continuous lifting of the ice, since ice flow was obstructed in the blue-ice area. From the profile of the pressure difference, the vertical distribution of the upward velocity was calculated, which provided a time-scale for the core. It was found that the 100 m long core represented a record of about 104–105a. Since the surface ice was considered to represent a few tens of thousand years B.P., the data obtained on total gas content, δ18O, and electrical conductivity would describe the variations in the climate as well as in the ice sheet during the last glacial period.
The Japanese Antarctic Research Expedition (JARE) has conducted glaciological studies on Mizuho Plateau since 1981. We have already reported that the ice sheet flowing from Mizuho Plateau into Shirase Glacier is thinning at a rate of about 70 cm/year and that the profile of the distribution of basal shear stress is similar to that of surging glaciers.A 5 year glaciological programme on Mizuho Plateau and in east Queen Maud Land is now being carried out and we have obtained the following new results:(1) The ice sheet in the down-stream region (where ice elevation is lower than about 2400 m) is thinning, based on measurements of horizontal and vertical flow velocity, strain-rate, the slope of the ice surface, the accumulation rate and densification of snow.(2) δ18O analysis of deep ice cores obtained at Mizuho Station (2240 m a.s.l.) and point G2 (1730 m a.s.l.) shows that δ18O increased about 200 years ago at Mizuho Station and about 400 years ago at point G2. If we can assume that the increase in δ18O is caused by the thinning of the ice sheet, then this result means that this thinning propagates to up-stream areas.(3) Radio-echo-sounding measurements on Mizuho Plateau show that the ice base in the down-stream region is wet. This supports the result described in (1), since the basal sliding due to a wet base causes ice-sheet thinning, as proposed in our previous studies.In summary, a possible explanation of ice-sheet variation on Mizuho Plateau is as follows: the thinning of the ice sheet, caused by the basal sliding due to basal ice melting, started at Shirase Glacier and has been propagating up-stream to reach its present position. A simple calculation, using flow velocities, shows that the thinning started at Shirase Glacier about 1500–2000 years ago.
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 6 18 0 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 6 18 0 profile is discussed. The shape of the 6 18 0 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 .
Air-hydrate inclusions have been found in deep ice cores from Dye 3, Greenland, which were taken in August 1981 . Although the concentration of the air-hydrate crystals decreased with time, when the core was stored at a temperature of -50°C, they still existed to an appreciable extent in 1985.An ice specimen was cut out from the Dye 3 core at a depth of 1500 m, where the volume fraction of the hydrate crystals was about 10-3 by volume. Its dielectric ?10
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