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Chemical and isotopic distribution in ice due to water freezing in Antarctica
Souchez, R.; Tison, J.-L. (1993). Chemical and isotopic distribution in ice due to water freezing in Antarctica, in: Caschetto, S. (Ed.) Belgian scientific research programme on Antarctica: scientific results of phase II (10/1988-05/1992): 3. Glaciology and climatology. pp. II/01/1-42
In: Caschetto, S. (Ed.) (1993). Belgian scientific research programme on Antarctica: scientific results of phase II (10/1988-05/1992): 3. Glaciology and climatology. Belgian scientific research programme on Antarctica. Belgian Science Policy Office: Brussel. 259 pp., meer
In: Belgian scientific research programme on Antarctica. Belgian Science Policy Office: Brussel. , meer
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| Abstract |
The isotopic and chemical properties of glacier ice in the Antarctic mostly reflect the climatic and environmental conditions under which snow was formed and transformed into ice. By constrast, ice due to water freezing has properties resulting from the action of completely different processes which characterize ice-ocean and ice-bedrock interfaces. The two main factors which influence the isotopic and chemical signals in ice during a water/ice phase change are the freezing rate and the characteristics of the parent water . When sea ice formation is governed by thermodynamical rather than dynamical processes, chemical and isotopic profiles fluctuating in opposite ways are the signatures of the dominant role played by a freezing rate effect. However, such situations are not always present. The isotopic and chemical characteristics of multi-year sea ice sampled in a rift of George VI Ice Shelf can only be understood if changes in parent water properties during the sea ice cover formation are taken into account. The dominating role of parent water effects over freezing rate effects result in sympathetic fluctuations between the two profiles: when ice is enriched in heavy isotopes, it is also enriched in salts and the reverse is equally true even at a small scale. In the case of the rift of George VI Ice Shelf, variable mixing of sea water with melt water from basal shelf ice plays the major role in explaining the distributions. In some circumstances. liquid water is present only in small amounts such as at the base of the ice sheet. Basal ice was encountered in Terre Adelie in a core drilled through the ice sheet margin and in a ramp at proximity of the sea. An isotopic and chemical study of this ice reveals the presence of liquid water at crystal boundaries at subfreezing temperatures and the role of small scale freezing events which explain the main characteristics of basal ice. A new mechanism of basal ice formation is proposed. |
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