What drives the mean along-shelf flow in the Northwest Atlantic coastal ocean?
Chen, K., & Yang, J. (2024). What Drives the Mean Along-Shelf Flow in the Northwest Atlantic Coastal Ocean? Journal of Geophysical Research: Oceans, 129(7), e2024JC021079. https://doi.org/10.1029/2024JC021079
Upper panel: along-shelf transport at the four cross-shelf sections: Middle Labrador Shelf, Southern Labrador Shelf, Scotian Shelf, and Middle Atlantic Bight. Results from three scenarios are shown: control experiment (ctrl, black circle), no wind stress experiment (noWind, red square), and no continental runoff experiment (noRiver, blue diamond). Transport is integrated from surface to bottom, from the coast to 200 m isobath. Lower panel: the influence of wind (ctrl-noWind) and buoyancy (ctrl-noRiv) on the along-shelf transport. Image provided by Ke Chen.
A long-standing hypothesis is that the steady along-shelf circulation in the Northwest Atlantic (NWA) coastal ocean is driven by buoyancy input from continental freshwater runoff. However, the influence of freshwater runoff has not been adequately evaluated or compared with other potential driving mechanisms. This study investigates the roles of both wind stress and freshwater runoff in driving the mean along-shelf flow in the NWA coastal ocean and examines other potential drivers using a newly developed high-resolution regional model with realistic forcing conditions. The results reveal that wind stress has a greater impact than freshwater runoff on the overall mean circulation and along-shelf sea-level gradient on the NWA shelf. While continental freshwater consistently contributes to equatorward along-shelf flow and a higher sea level along the coast, wind stress is more effective in setting up the broad-scale circulation pattern, driving the along-shelf flow on the Labrador Shelf and opposing it in the Mid-Atlantic Bight and the Scotian Shelf. In addition to local wind and freshwater runoff, sub-Arctic inflow from higher latitudes is an essential component of the NWA shelf circulation system. This remote driver directly influences the along-shelf flow and helps insulate the shelf flow from the Gulf Stream on the southern shelves.