Local wind and open-ocean forcing of circulations on the Northwest Atlantic shelves

Previous studies have emphasized the importance of buoyancy forcing, particularly the freshwater flux from major rivers in the region, in maintaining the mean equatorward flow on the Northwest Atlantic shelves from the Greenland coast to Cape Hatteras. The contributions from wind-stress forcing and deep-ocean processes is less studied. In this study, we use a basin-wide two-layer model with realistic topography and wind stress forcing to examine how circulation and its seasonal variability between Cape Hatteras and Baffin Bay shelf respond to local and remote wind-stress forcing and how and where ageostrophic processes facilitate cross-shelf influences from open-ocean processes. With wind-stress forcing alone the model simulates a mean shelf circulation system that resembles remarkably well with observed and OGCM-simulated features. The along-shelf transport from Baffin Bay to Cape Hatteras is well within the range of previous data-based estimates. In addition, the seasonal variability of the wind-driven transport along the shelf is consistent with what has been described in previous studies. It was found that the wind stress on shelves is the leading forcing mechanism for both the mean transport and its seasonal variability. The wind stress not only affects local transport but also influences circulation downstream in the direction of topographic waves. Our study also indicates that the open-ocean processes play an important secondary role. A regional high-resolution OGCM is used to examine the robustness of mechanisms that are identified in the two-layer model and to examine the how buoyancy forcing may affect such mechanisms/processes.