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Gas Diffusion and Fractionation in Clathrated Ice-Core Samples (Abstract)

Published online by Cambridge University Press:  20 January 2017

J. Ocampo
J. Ocampo*
Affiliation:
Laboratoire de Glaciologie et de Géophysique de l’Environnement, B.P. 96, 38402 St Martin d’Hères Cédex, France
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Abstract

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The evolution of gas content from clathrated ice is very sensitive to pressure and to storage temperature. As such substances are likely to be found in deep Antarctic ice and the Greenland ice sheet (Miller 1969, Shoji and Langway 1982), the influence of clathrate formation and incomplete back-diffusion on the measured air composition was investigated.

We have undertaken laboratory studies on the kinetics of formation and decomposition of clathrate hydrates of air and carbon dioxide. The kinetics were found to be controlled mainly by the self-diffusion of water molecules. The clathrate structure being of type II (Davidson and others 1984), the diffusion of guest molecules and the role of auxiliary gases was studied.

A bubble-relaxation model is presented for air-hydrate inclusions in fresh ice cores. It takes into account the diffusion constant for desorption of clathrates and the mechanical relaxation of the bulk ice. The increasing pressure and the initially low bubble surface are factors which limit the rate of decomposition. The rate of decomposition was compared with the natural bubble relaxation measured in deep ice cores (Gow and Williamson 1975).

Fractionation was also observed through the formation and decomposition of mixed hydrates. The diffusion control of the recrystallization process affects this fractionation.

On the basis of this study we make some recommendations for the analysis of deep ice-core samples.

Type
Abstract
Information
Annals of Glaciology , Volume 10 , 1988 , pp. 214
Copyright
Copyright © International Glaciological Society 1988

References

Davidson, D W, Handa, Y P, Ratcliffe, C I, Tse, J S, Powell, B M 1984 The ability of small molecules to form clathrate hydrates of structure II. Nature 311(5982):142–143 Google Scholar
Gow, A J, Williamson, T 1975 Gas inclusions in the Antarctic ice sheet and their glaciological significance. Journal of Geophysical Research 80(36): 5101–5108 Google Scholar
Miller, S L, 1969 Clathrate hydrates of air in Antarctic ice. Science 165(3892): 489–490 Google Scholar
Shoji, H, Langway, C C Jr 1982 Air hydrate inclusions in fresh ice core. Nature 298(5874): 548–550 CrossRefGoogle Scholar