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Chemical signatures of clear basal ice facies at the margins of dry-based glaciers, South Victoria Land, Antarctica

Bronwyn L. Hooker
Department of Geography, University of Otago, Dunedin, New Zealand

 
Abstract

Few studies have been undertaken into the basal ice chemistry of dry-based glaciers such as those in the Dry Valleys of Antarctica. Holdsworth (1974) proposed solid-state diffusion as a mechanism for solute enrichment in dry-based glaciers, and recent stratigraphic, isotopic, and gas content studies suggest that the refreezing of liquid water at the base of some glaciers may occur, perhaps by accretion as ice contacts proglacial lakes. This thesis reports the results of a reconnaissance study of the base cation and chloride concentrations of clear basal ice facies, glacier ice and proglacial lake waters. The ice facies and lake waters of seven glaciers in the Dry Valleys, six of which were dry-based, were sampled, melted and filtered in the field. The results of atomic absorption spectrophotometer, and flow injection analyses show that base cation and chloride concentrations of clear basal ice in most glaciers adjacent to proglacial lakes were higher than in glacier ice formed by the metamorphism of snow. Samples of clear basal ice also had a considerably lower solute content than in adjacent lake water, although the clear basal ice varied considerably. Four models that may explain the observed patterns were examined. Firstly, regelation is unlikely unless peculiar conditions of basal melting occur beneath dry-based glaciers Secondly, solid-state diffusion may be responsible for the enrichment of some sites, but not those that are highly elevated, because of the long period required for diffusion. Thirdly, apron incorporation is inappropriate for solute-enriched basal ice but may be responsible for basal layers with no enrichment, since aprons have the same chemical composition as glacier ice. Finally, proglacial lake ice/debris accretion may result if a closed system occurs at the glacier/lake interface of some glaciers. The solute data indicate that lake water accretion could result in a higher chemical concentration of basal ice than lake ice, however the chemistry alone is not a reliable indicator of the origin of basal ice.

 
Reference

Hooker, B.L. 1998. Chemical signatures of clear basal ice facies at the margins of dry-based glaciers, South Victoria Land, Antarctica. Unpublished MSc thesis, in Geography, at the University of Otago, Dunedin, New Zealand. 96 pp.

© 2009 Department of Geography, University of Otago, Dunedin, New Zealand