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Chemical and isotopic composition of ice from Antarctic ice shelves: implications for global change
Souchez, R.; Tison, J.-L.; Lorrain, R. (1997). Chemical and isotopic composition of ice from Antarctic ice shelves: implications for global change, in: Caschetto, S. (Ed.) Belgian research programme on the Antarctic: scientific results of phase III (1992-1996): 3. Glaciology and climatology. pp. A3/11/002/1-48
In: Caschetto, S. (Ed.) (1997). Belgian research programme on the Antarctic: scientific results of phase III (1992-1996): 3. Glaciology and climatology. Belgian scientific research programme on Antarctica. Federal Office for Scientific, Technical and Cultural Affairs: Brussel. 149 pp., meer
In: Belgian scientific research programme on Antarctica. Belgian Science Policy Office: Brussel. , meer
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| Abstract |
In the context of global warming, the question of the stability of Antarctic ice shelves is critical for predicting any sea level rise. Small ice shelves are likely to react more rapidly than large ones to a change in atmospheric and oceanic temperatures. Therefore, understanding their behaviour is a priority in Antarctic glaciological research. The behaviour of ice shelves and floating ice tongues is dependent on their boundary conditions. At the ice-ocean interface, these boundary conditions can be appraised by studying the properties of marine ice forming accretions at the base . In this study, attention is drawn on two case studies, both in the Terra Nova Bay area, Victoria Land. A. In the first case, marine ice is formed near the grounding line here defined as the limit between grounded ice and floating ice, either if the glacier goes afloat or becomes again grounded. Two different types of marine ice have been found. Type 1 is bubble-and debris-free ice with properties which can be explained by intrusion of brackish water in open basal fissures. Closing of the fissures by progression of a freezing front from the sides is precluded and filling by frazil ice is favoured. Type 2 is made of thin clear ice and debris layers which are thought to have formed when a subglacial water-filled sediment enters into contact with sea water and is subjected to freezing under a double diffusion process. It is also stressed that, in a δD-δ18O diagram, the alignment of marine ice samples on a mixing line does not, necessarily, imply a mixture of continental water and sea water in varying proportions. B. In the second case, extensive frazil ice accumulation occurs under the ice shelf. Different frazil ice types can be identified which have different crystallographic, isotopic and chemical characteristics. Results from oceanic water sampling at various time periods clearly show the occurrence of ice shelf water (ISW) circulation mode 3. In this mode, tidal pumping allows seasonally warm waters of the coastal currents to make contact with the base of the ice shelf and to produce melting. The wide occurrence of orbicular frazil ice accreted at the bottom of the ice shelf is the result of circulation mode 1 i.e. deep thermohaline circulation. Banded frazil ice is probably generated by a double-diffusion process at the limit between ISW-mode 1 and ISW-mode 3, thus partially impeding the net melting loss due to circulation mode 3. |
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