Seasonal circulation on the western and central Scotian Shelf

A realistic representation of 3D seasonal circulation and hydrography on th e western and central Scotian Shelf has been obtained from historical obser vations and a combination of diagnostic and prognostic numerical models wit h forcing by tides, wind stress, and baroclinic and barotropic pressure gra dients. The major current features-the southwestward Nova Scotian and shelf -edge currents, and partial gyres around Browns and Sable Island Banks-are found to persist year-round but with significant seasonal changes. Comparis on with current meter observations shows good agreement for the Browns Bank , southwest Nova Scotia, and inner-shelf regions, and poorer agreement in t he Sable Island Bank and shelf-edge regions where current and density obser vations are sparser and tidal influences weaker. There is significant spatial structure in the seasonal circulation and hydr ography, and in the underlying dynamical processes. On the shelf scale ther e are substantial changes in stratification, potential energy, and alongshe lf throughflow between the central and western areas, related to topography , different tidal regimes, and proximity to major water mass sources. The b aroclinic pressure field is the predominant shelf-scale forcing, but there are important cross-shelf meanders of the throughflows associated with topo graphy. The partial bank gyres are connected to the throughflows and have m ultiple, and in some cases, opposing forcings. Tidal rectification and baro clinic flow dominate on Browns Bank, with a relatively small wind influence on the climatology, while baroclinic flow and barotropic inflow from the s helf edge are important on Sable Island (including Western) Bank. The flows are generally clockwise (counterclockwise) over the shallow (deep) area, b ut have substantial vertical shear. The combination of spatial structure, m ultiple forcings, and other flow components provides the potential for stro ng sensitivity of drift to location and time.