Air bubbles and air-hydrate crystals in the Vostok ice core

Source: OAI

ABSTRACT International Symposium on Physics of Ice Core Records. Shikotsukohan, Hokkaido, Japan, September 14-17, 1998. The geometrical properties of air-bubble and air-hydrate ensembles in the 3310-m deep Vostok core and in other ice cores were studied. The principle results are the following: 1) the size and abundance of air bubbles in polar ice depend on the temperature and accumulation rate prevailing over the time of the snow-ice transformation, 2) the climate signal imposed on the bubble properties at pore close-off is only slightly modified in the course of the bubble-hydrate transition (500–1250 m at present time at Vostok) and in the first, transient, phase of air-hydrate crystal growth (1150–1500 m); as a consequence, the last four glacial-interglacial cycles are resolved in variations of the number and size of air inclusions along the Vostok ice core, and 3) the air-bubble and air-hydrate records from polar ice cores can provide an independent experimental constraint on the temperature-accumulation relations in the past.

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    ABSTRACT: This work presents a method of mapping deformation-related sublimation patterns, formed on the surface of ice specimens, at microscopic resolution (3–4 mm pixel –1). The method is based on the systematic sublimation of a microtomed piece of ice, prepared either as a thick or a thin section. The mapping system consists of an optical microscope, a CCD video camera and a computer-controlled xy-stage. About 1500 images are needed to build a high-resolution mosaic map of a 4.5 Â 9 cm section. Mosaics and single images are used to derive a variety of statistical data about air inclusions (air bubbles and air clathrate hydrates), texture (grain size, shape and orientation) and deformation-related features (subgrain boundaries, slip bands, subgrain islands and loops, pinned and bulged grain boundaries). The most common sublimation patterns are described, and their relevance for the deformation of polar ice is briefly discussed.
    Journal of Glaciology 01/2006; 52(178). · 2.88 Impact Factor
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    Journal of Geophysical Research 01/2006; 111. · 3.17 Impact Factor
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    ABSTRACT: Ancient atmospheric gases are trapped in polar ice sheets. The gas molecules are stored in air bubbles at shallow depth and are incorporated into clathrate hydrates below a depth at which the hydrostatic pressure becomes greater than the formation pressure of the air clathrate hydrate. Significant gas fractionation has been found from measurements of the depth profile of the N2/O2 composition ratios in clathrate hydrates and air bubbles of Vostok antarctic ice. To investigate the effect of the ice condition on the fractionation process, we measured the N2/O2 ratios in clathrate hydrates and air bubbles from Dome Fuji antarctic ice using Raman spectroscopy. The results showed that the N2/O2 ratios in the clathrate hydrates of the Dome Fuji ice are slightly lower than those of the Vostok ice, although the tendency of the variation of the N2/O2 ratio with depth is similar. The difference in the N2/O2 ratio between the Dome Fuji ice and the Vostok ice for the transition zone is attributed to the difference of the ice temperature and the snow accumulation rate. On the other hand, it is concluded that the difference in the bubble-free ice zone was caused by gas loss from the ice core after coring. The N2/O2 ratio of clathrate hydrate increases after coring because of higher diffusion rate and lower dissociation pressure of O2 than of N2. Our data suggest that the effect of gas loss in the Dome Fuji ice is relatively small, and so the gas composition in the Dome Fuji ice can be a precise paleoenvironmental indicator.
    Journal of Geophysical Research 01/2001; 106:17799-17810. · 3.17 Impact Factor


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