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Ice composition evidence for the formation of basal ice from later water beneath a cold-based Antarctic glacier

R. D. Lorrain1, S. J. Fitzsimons2, M. J. Vandergoes2, and M. Stiévenard3

1 Département des Sciences de la Terre et de l'Environnement, Université Libre de Bruxelles, B-1050 Bruxelles, Blegium
2 Department of Geography, University of Otago, Dunedin, New Zealand
3 Laboratoire des Sciences du Climat et de l'Environnment, Laboratoire mixte CEA-CNRS-CE Saclay, F-91191 Gif-sur-Yvette Cedex, France

 
Abstract 

Entrainment of debris by cold-based glaciers having basal temperatures as low as -17°C can be observed in the Dry Valleys of south Victoria Land, Antarctica. The classical models developed to explain debris incorporation at the glacier base are inappropriate in such cases, since the basal temperature is well below the freezing point. An alternative model, based on the presence of ice-marginal lakes, has recently been proposed by one of the authors (S. F.). In this model, transient wet-based conditions can occur as ice flows onto the unfrozen sediments of the lake bottom, creating conditions favourable to the entrainment of sediments and to ice accretion by water freezing.
Here we describe a situation where this model is consistent with an ice-composition study of the basal part of Suess Glacier, Taylor Valley. The stable isotope composition indicates that water freezing, most probably lake water, plays a major role in the formation of the basal ice layers. Total gas content of this basal ice is considerably depleted when compared to meteoric glacier ice, in accordance with a rejection mechanism during freezing. Its gas composition, strongly enriched in CO2, is also indicative of the presence of a former liquid phase.

 
Reference
Lorrain, R.D., Fitzsimons, S. J., Vandergoes, M. J. and Stiévenard, M. 1999. Ice composition evidence for the formation of basal ice from lake water beneath a cold-based Antarctic glacier. Annals of Glaciology, 28, 277-281. [PDF 257kb]

 

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