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The microstructure of meteoric ice from Vostok, Antarctica
The 3623 m long, 5G core collected at Vostok station, Antarctica, contains alternating layers of meteoric ice with two distinctly different microstructures. In this paper, we present the microstructure and impurity content of a number of specimens ranging in depth from 97 to 3416m, describe in detail the characteristics of the different layers and propose a mechanism for their microstructural development. Digital image analysis, ion chromatography, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to measure texture and the location and type of impurities; electron backscatter diffraction was used to determine crystal orientation. The ice associated with interglacial periods is characterized by relatively coarse grains and a strong preferred orientation of the caxes in a plane encompassing the coring direction, producing a vertical-girdle fabric. In contrast, ice from glacial periods is characterized by a much smaller grain size and a strong single-maximum fabric, where the c axes are clustered around the vertical. Calcium is uniquely present in the grain boundaries of the fine-grained glacial layers, and its effect on grain-boundary mobility and the misorientation dependence of mobility can explain the development of the discontinuous microstructure seen in glacial ice at Vostok station.
International Glaciological Society
ISSN : 0022-1430 CODEN : JOGLAO
Journal of Glaciology A. 2007, vol. 53, n° 180, pp. 41-62 [22 pages] [bibl. : 1 p.1/4]
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