Drifting buoy data, surface pressure, and geostrophic wind analyses from the Arctic Ocean Buoy Program are used to examine seasonal features of the sea ice motion in the Canada Basin for 1979–1985. Although the 7‐year annual mean motion in this region is clockwise, the month‐to‐month motion is highly variable. In late summer to early autumn, the circulation can become net anticlockwise for periods lasting at least 30 days. Results from a linear model demonstrate that these “reversals” of ice motion in the Beaufort Gyre are a wind‐driven response to persistent cyclonic activity that contrasts sharply with the predominantly anticyclonic regimes of spring, late autumn, and winter. Model‐predicted ice divergences of 0.5% or more per day which can occur during periods of anticlockwise ice motion are in good agreement with values calculated from optimally interpolated velocity gradient fields. Visible band imagery and passive microwave data confirm associated large areal reductions in ice concentration of approximately 20%. Data from under‐ice submarine sonar transects and surface pressure records prior to the study period point to frequent recurrences of these late summer to early autumn ice conditions.

A data base of ice draft and roughness parameters has been constructed for selected portions of the Arctic Ocean based upon analysis of under‐ice draft distribution data acquired by inverted echo sounder systems on submarines. From the voyages of 12 submarines which traversed the Alaskan, Canadian, and central Arctic regions of the Arctic Ocean during the summer and winter seasons, a series of mean ice draft and deep‐draft keel statistics was calculated for 50‐km segments along each submarine track. Contour maps of the mean ice draft, its standard deviation, the mean keel draft, and the spatial frequency of ice keels were constructed. They show that the greatest ice drafts, the roughest ice, and the greatest number of deep‐draft keels are found off the north coasts of the Canadian Archipelago and Greenland due to ice convergence on these land barriers.

A submarine sonar profile obtained in Davis Strait by USS Queenfish in February 1967 has yielded the first quantitative data on ice thickness distribution in the region. Within 50–100 km of the ice edge there is a “marginal ice zone” (MIZ) where the mean draft is 0.25–0.51 m, most of the ice (93–100%) is undeformed, and there are many leads but few ridges, all of them less than 6.1 m in draft. The remainder of the region is an “interior zone” composed mainly of first‐year ice with a mean draft of 0.77–1.66 m, increasing slightly from NE to SW. Level ice is less common than in the MIZ (67–91% of the cover) as are leads. Ridging is more common, with a maximum observed keel draft of 19.56 m. The overall mean ice thickness distribution has a peak at a draft of 1.05 m (1.18 m thickness), identified as the preferred draft of undeformed first‐year ice at this time. Ice draft and keel draft distributions followed a negative exponential distribution at depths beyond 3–4 m, and the distribution of lead widths followed a power law with exponent −2.29.

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 profiles were recorded. In August 1970 USS Queenfish (SSN‐651) retraced Nautilus' route, yielding the only duplicate transect of under‐ice topography across the Arctic Basin. Comparisons of the statistical analysis of the under‐ice draft measurements obtained through use of wide‐beam and narrow‐beam and narrow‐beam only acoustic profilers by Nautilus and Queenfish, respectively, along the coincidental route are presented. Geographic areas found to have distinct under‐ice characteristics and ice composition are identified. The under‐ice statistics of both cruises are considered in relation to representative field observations and modeling results of other researchers. Principal findings are (1) Nautilus recorded generally more severe ice conditions within the Canada Basin than did Queenfish 12 years later; overall mean drafts were 3.08 and 2.39 m, respectively, (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 may contain the most moderate under‐ice topography and the greatest number of open water and refrozen polynyas and leads within the central Arctic Basin, (4) the Makarov and Amundsen basins and the Arctic mid‐ocean ridge may contain some of the most severe under‐ice topography within the Arctic Basin, and (5) the present study indicates an overall Arctic Basin mean of 3–4% open water/new ice (less than 30 cm) in summer.

Ice velocities and sea level pressure data from Arctic drifting buoys for 1979-85 are used to examine the seasonal variation of sea ice drift in the Canada Basin. A recurring reversal of the mean anticyclonic gyre is demonstrated in late summer, in response to changes in atmospheric forcing. The identification of this reversal of ice motion is significant for numerical modeling of Arctic atmosphere-ocean-ice interactions. Introduction The drift of sea ice in the Arctic Basin has been extensively investigated since Nansen's famous voyage in the "Fram", 1894-96. The main features of the mean pattern of ice circulation [Fel'zenbaum, 1958; Gordienko, 1958] are a large-scale drift away from the Siberian coastline and across the Pole in the Transpolar Drift Stream, with ice exiting the basin through the Fram Strait between Greenland and Svalbard. In the Canada Basin, the motion of the surface waters and ice is characterized by the clockwise Beaufort Gyre that corresponds roughly to the mean surface anticyclone in the atmosphere [Campbell, 1965; Newton, 1973; Carmack, 1986]. Mean velocities of ice drift in the gyre are about 5-6 km d -•. The AIDJEX program in the southern Beaufort Sea investigated ice behavior on a 100 km space scale and one day time scale [Pritchard, 1980]. Subsequently, basin scale data on ice motion have been provided by a network of Arctic drifting buoys [Thorndike and Colony, 1980]. Recent analysis of submarine sonar measurements of ice draft collected by the USS NAUTILUS in August 1958 and the coincident August 1970 transect of the USS QUEENFISH across the Canada Basin along 155 o W indicates that the ice in the central part of the Beaufort Gyre may be thinner and more open than elsewhere [McLaren, 1986] contrary to the earlier interpretation of the NAUTILUS data by Lyon [1961]. McLaren's analysis provided the impetus for a study of ice motion in the Canada Basin. The long-term mean ocean gyre accounts for up to half of the mean ice motion in the Canada Basin, away from coastal areas, but about 70 percent of the variance of the daily ice velocity is contributed by the geostrophic winds [Thorndike and Colony, 1982]. Felzenbaum [1958, cited in Campbell, 1965] notes that surface currents in the Arctic Basin vary little over intervals of Numerical simulation of northern hemisphere sea ice variability, 1951-1980. 90(C3), 4847-4865, 1985.