Seasonal Circulation on the Western and Central Scotian Shelf*

Abstract

A realistic representation of 3D seasonal circulation and hydrography on the western and central Scotian Shelf has been obtained from historical observations and a combination of diagnostic and prognostic numerical models with forcing by tides, wind stress, and baroclinic and barotropic pressure gradients. 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. Comparison with current meter observations shows good agreement for the Browns Bank, southwest Nova Scotia, and inner-shelf regions, and poorer agreement in the Sable Island Bank and shelf-edge regions where current and density observations are sparser and tidal influences weaker. There is significant spatial structure in the seasonal circulation and hydrography, and in the underlying dynamical processes. On the shelf scale there are substantial changes in stratification, potential energy, and alongshelf throughflow between the central and western areas, related to topography, different tidal regimes, and proximity to major water mass sources. The baroclinic pressure field is the predominant shelf-scale forcing, but there are important cross-shelf meanders of the throughflows associated with topography. The partial bank gyres are connected to the throughflows and have multiple, and in some cases, opposing forcings. Tidal rectification and baroclinic flow dominate on Browns Bank, with a relatively small wind influence on the climatology, while baroclinic flow and barotropic inflow from the shelf edge are important on Sable Island (including Western) Bank. The flows are generally clockwise (counterclockwise) over the shallow (deep) area, but have substantial vertical shear. The combination of spatial structure, multiple forcings, and other flow components provides the potential for strong sensitivity of drift to location and time.