Analysis of the Under-Ice Topography in the Arctic Basin as Recorded by the USS Nautilus during August 1958

The USS Nautilus (SSN-571) was the first vessel to cross the Arctic Basin via the North Pole in early August 1958. During this expedition almost continuous acoustic under-ice thickness distribution profiles were recorded. This article presents an overall statistical analysis of the under-ice draft measurements obtained during this historic cruise. Geographic areas found to have distinct under-ice-characteristics and ice compositions are identified. Principal findings are: (1) Nautilus recorded an overall mean under-ice draft of 3.68 m across the Arctic Basin; (2) the under-ice topography becomes progressively more severe when proceeding from the Canadian to the Eurasian side of the Arctic Basin; (3) the Canada Basin was observed to contain the most moderate under-ice topography and the greatest number of open water and referent polynyas and leads along the transpolar route taken by Nautilus; (4) Nautilus encountered the most severe under-ice topography of the voyage over the Arctic Mid-Ocean Ridge; and (5) an overall Arctic Basin mean of 2.6% open water/new ice (<30 cm) was encountered during her voyage beneath the sea ice cover of the Arctic Ocean.Key words: sea ice, under-ice thickness distribution, sonar, Canada Basin, Central Arctic, Eurasian Basin, arctic submarineMots clés: glace de mer, distribution de l’épaisseur de la glace mesurée par dessous, sonar, bassin canadien, centre de l’Arctique, bassin eurasien, sous-marin arctiqu

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

Submarine profiles of the ice underside in M'Clure Strait were obtained by USS Sargo in February 1960 and by USS Seadragon 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 SoundMots clés: glace de la mer, crêtes de pression, sonar, le détroit M'Clure, le détroit Viscount Melvill