Ocean Circulation and Shelf-basin Exchanges in the Canada Basin from a High Resolution Model

Results from a high-resolution coupled Arctic Ocean and sea ice model are analyzed to describe the water circulation and exchanges in the Canada Basin and the adjacent shelves. Seasonal and interannual variability is modeled with 1979-1998 forcing derived from the European Centre of Medium-range Weather Forecasts (ECMWF) reanalyzed and operational atmospheric data. Results from the 18-km model show complex hydrographic and dynamic structures with high spatial and temporal variability in water properties, currents, and volume transports. A schematic time-averaged flow of water masses in the Canada Basin can be described by a three-layer circulation driven by the atmospheric and thermohaline forces. The bottom topography is shown to considerably influence current patterns and structures. The deep layer is mostly thermohaline driven with a slow cyclonic flow. The hydrographic fields and current structure within the intermediate layer show an anticyclonic, geostrophically-balanced circulation. The rising of isohaline surfaces near the continental margins represents a relatively strong (of order 5 cm/s) anticyclonic boundary current along the slope. Over the longer time periods the atmospheric forcing is transmitted into the deeper water column and contributes to the dynamics of intermediate and deep waters. The surface layer circulation over the shelves is mostly wind-driven. In the basin, this flow is also affected by the thermohaline circulation of the deeper layers. The large-scale currents change significantly during the time of simulation. The cyclonic and anticyclonic modes of circulation are identified. The cyclonic mode promotes shelf-basin exchanges between the Chukchi/Beaufort Seas and the Canada Basin. The deep basin circulation and exchanges between northern and southern part of the Canada Basin intensify during the anticyclonic mode. In the early 1990s an increased advection of Atlantic Water (AW) over the Mendeleyev Ridge occurs. AW flows along the East Siberian shelf slope, circulates to the north over the Arlis Plateau and Mendeleyev Ridge. In 1993 it crosses the Mendeleyev Ridge and a tongue of AW at depths of 200-1000 m continues eastward with a core mean velocity of ~0.5 km/day. By 1996 AW reaches the northern end of the Chukchi Cap and enters the central Canada Basin. Results from the 18-km model will be also compared with output from the new 9-km coupled ice-ocean model.