Sir,
There is a growing need for a revision and extension of the definitions of ice features met with in Antarctica. The suggestion made below is just one of those which must inevitably arise as detailed work proceeds in Antarctic regions. It would be valuable if some sort of international agreement could be reached before publication of I.G.Y. and later work proceeds too far, and the recent S.C.A.R. move to adopt uniform cartographic symbols for ice features is welcomed. The “Illustrated ice glossary” (Armstrong and Roberts)Reference Armstrong and Roberts 1 provides the basis for an agreement of this sort, but further work is required, as the example given below will illustrate.
There are, in Antarctic waters, three main types of islands. First is the ordinary rocky island, which in summer is bare or incompletely covered with ice. Secondly, there is the ice-capped island, whose rocky base rises above sea level and is visible around the edge, but which is covered by a layer of permanent ice, nourished by snowfall and by frozen sea spray. (Such islands are generally small.) Finally, there is the “Ice Island,” which is generally dome-shaped and which displays no rock at all. In some cases its rocky base does not rise above sea-level, but nevertheless forms the anchorage for the permanent ice cap. In other cases the rocky base may rise above sea-level somewhere beneath the ice; but it is nowhere visible and, from the sea, all that can be seen are ice cliffs. These latter two could only be distinguished by seismic ice depth measurements. (Such islands are generally large.) Diagrams 1 to 4 (p. 1166) show these three types.
To permit uniformity of description of these features in the literature I would like to propose the following nomenclature:
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Diagram (1) Island
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Diagram (2) Island (descriptively it could be referred to as an ice-capped island)
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Diagrams (3) and (4) Ice islands
Typical ice islands are Drygalski Island in the Davis Sea (near Mirnyy) and White Island near Amundsen Bay (Enderby Land).
I realize that the term “ice island” is already in use in Arctic regions for the large floating icebergs broken from the ice shelf off Ellesmere Island. However, these floating, drifting features cannot in any sense be regarded as islands and I see no point in perpetuating such a misnomer at the expense of correct terminology in Antarctica. The Arctic features could be re-defined as “Ellesmere icebergs,” island icebergs “iceberg islands,” or some other term.
The term “ice rise” (Armstrong and Roberts) I consider less suitable geomorphologically for the Antarctic feature.
To be more specific I would suggest the following definition:
Ice island
An elevation of the sea bed, not within the confines of an ice shelf, permanently capped with ice projecting above sea-level but with no rock visible above sea-level.
The term “ice-capped island” would be largely a descriptive term because, cartographically, this feature would be regarded as an ordinary island.
Following the S.C.A.R. decision to use the prefix “sub-glacial” before ordinary generic terms to designate features which are beneath Antarctic ice, it should be pointed out the Diagram (4) illustrates a “sub-glacial island.” However, until seismic ice-depth determinations are carried out, such a fact will not be known. One would expect, therefore, that as exploration proceeds some “ice islands” will be reclassified as “sub-glacial islands” for cartographic purposes, although for descriptive purposes the name “ice islands” would probably be retained.
