AIR-HYDRATE CRYSTALS IN DEEP ICE-CORE SAMPLES FROM VOSTOK STATION, ANTARCTICA

Microscopic observation of air-hydrate crystals was carried out using 34 deep ice-core samples retrieved at Vostok Station, Antarctica. Samp les were obtained from depths between 1050 and 2542 m, which correspon d to Wisconsin/Sangamon/Illinoian ice. It was found that the volume an d number of air-hydrate varied with the climatic changes. The volume c oncentration of air-hydrate in the interglacial ice was about 30% larg er than that in the glacial ice. In the interglacial ice, the number c oncentration of air-hydrate was about a half and the mean volume of ai r-hydrate was nearly three times larger than that in the glacial-age i ce. The air-hydrate crystals were found to grow in the ice sheet, abou t 6.7 x 10(-12) cm3 year-1, in compensation for the disappearance of s maller ones. The volume concentration of air-hydrate was related to th e total gas content by a geometrical equation with a proportional para meter alpha. The mean value of alpha below 1250 m, where no air bubble s were found, was about 0.79. This coincided with an experimentally de termined value of the crystalline site occupancy of the air-hydrate in a 1500 m core obtained at Dye 3, Greenland (Hondoh and others, 1990). In the depth profile of calculated alpha for many samples, alpha in t he interglacial ice was about 30% smaller than that in the glacial-age ice.