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 Unpublished MSc thesis, in Geography, at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.
