The Sea Ice Topography of M'Clure Strait in Winter and Summer of 1960 from Submarine Profiles

Abstract

ABSTRACT. Submarine profiles of the ice underside in M'Clure Strait were obtained by USS Sorgo in February 1960 and by USS Seadmgon in August 1960. They gave the first quantitative measurements of the ice draft distribution in the strait and in the nearby Beaufort Sea shelf zone, as well as providing a seasonal comparison of ice conditions within a single year. Analysis of the profiles reveals a region of very high mean ice draft (7.8 m) and heavy ridging off the southwest tip of Prince Patrick Island in winter. Within M'Clure Strait itself the mean ice draft lay in the 4-5 m range and the draft distribution showed that the ice was mainly first-year, as opposed to the mixture of first-and multi-year ice that exists out in the Beaufort Sea. This suggests a local origin for the ice in the strait. Pressure ridges were much more frequent in summer than in winter, as were polynyas. Both the pressure ridge draft distribution (in summer) and the ice draft distribution at great depths (in summer and winter) fitted a negative exponential distribution, in common with other ice profiles which have been analysed. Key words: sea ice, pressure ridges, sonar, M'Clure Strait, Viscount Melville Sound RfiSUMk. Des profils sous-marins de la surface infkrieure de la glace dans le dktroit M'Clure furent obtenus par 1'U.S.S. Sorgo en fCvrier, 1960 et par 1'U.S.S. Seadragon en aoOt, 1960. Ceux-ci ont pksentCs les premibres mesures quantitatives sur la distribution du tirant de la glace dans le detroit et dans la zone du plateau de la mer de Beaufort voisine, et ont aussi fourni une. comparaison saisonnibre des conditions glaciales pendant une ann&. L'analyse des profiles a kvClC une region au large de I'extkmitC sud-ouest de l'île Prince Patrick bu, durant l'hiver, le tirant moyen de la glace Ctait trbs important (7.8 m) et où d'tpaisses &tes Ctaient formt?es. Dans la ddtroit &me, le tirant moyen de la glace variait entre 4 et 5 met la distribution indiquait que la glace &it surtout de premiere ann&, par opposition au mClange de glace plus Ag& celle de premibre ande que l'on trouve dans la mer de Beaufort. Cette composition suggbre une origine locale pour la glace du dttroit. Les cdtes de pression Ctaient beaucoup plus frQuentes et Ct C qu'en automne, et tel Ctait aussi le cas pour les polynies. La distribution du tirant des cr&tes de pression (durant l'kt6 et l'hiver) suivaient une distribution exponentielle nCgative telle que celle d'autres profils de glace dCjh analyds.

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