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Ice-Shelf Underwater Morphology

Published online by Cambridge University Press:  30 January 2017

Olav Orheim
Olav Orheim*
Affiliation:
Norsk Polarinstitutt, Rolfstangveien 12, Postboks 158, 1330 Oslo Lufthavn, Norway
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Abstract

A side-scan sonar survey was conducted near the ice front of Riiser-Larsenisen during the 1976–77 Norwegian Antarctic Research Expedition to investigate the underwater ice-shelf morphology. The survey covered several shorter, widely-spaced sections, for a total of about 10 km along the ice front. Only a smaller part of the sections showed a smooth, straight ice front. Most of the observed ice fronts were very rough at the scale of decametres. Projections at around l00 m water depth commonly extended 50–200 m seaward of the above-water ice shelf, and had widths of similar dimensions.

Type
Abstracts of Papers Presented at the Symposium but not Published in Full in this volume
Information
Journal of Glaciology , Volume 24 , Issue 90 , 1979 , pp. 481 - 482
Copyright
Copyright © International Glaciological Society 1979

For each section the sonar was towed at one water depth only. Reflections are recorded from the nearest part of the ice shelf, which may occur at varying depths along the section. This complicates the interpretations. To solve this problem we plan to tow the sonar at several depths along ice-shelf fronts and icebergs during the 1978–79 expedition, for better three-dimensional information on the underwater morphology.

Discussion

G. de Q. ROBIN: I will be discussing the question of melting of the ice front on Wednesday—and will conclude that melting will be greater at greater depths. I am glad to see this information and to learn how irregular this melting can be. Did you find any cases where the ice shelf jutted out below sea-level? I expect this would worry the ship's Captain even more.

O. ORHEIM: It clearly would! I cannot remember any examples of the kind described from the Maudheim expedition, but they may have been present.

R. H. THOMAS: Did the ice front above sea-level show any distinctive features in the areas where these submarine rams were found?

ORHEIM: The recordings were done by an instrument trailing some hundreds of metres behind the ship, and by the time we were aware of them the area was far away, and we had no opportunity to re-examine the ice shelf, so I cannot answer your question adequately. Next season we shall do detailed under-water profiling of the ice shelf and will then also of course study the part above water.