Seasonal Variations and Driving Factors of the Eastern Maine Coastal Current

Abstract

AbstractTo investigate the coastal current in the Gulf of Maine (GoME) and its relation to forcing from outside of the gulf, a high‐resolution circulation model was developed and validated. Our model shows that the Eastern Maine Coastal Current (EMCC) possesses two cores, an offshore and a nearshore core that peak in summer and spring, respectively. The two cores can be traced back to outflows from the Bay of Fundy from opposite sides of Grand Manan Island, and both cores are deeper and slightly more onshore in summer and fall in response to tidal mixing, surface thermal stratification and wind. The two cores merge south of Pleasant Bay, then split into two branches again east of Mount Desert Rock, where the nearshore branch flows along the coast, while the offshore branch turns southward to recirculate in the eastern GoME. Subject to variations of Scotian Shelf Water and Slope Water (SW) inflows, the offshore veering occurs further upstream (northeastward) in late winter and summer, but gradually shifts downstream (southwestward) from summer to winter. Diagnosis of momentum balance demonstrates that the EMCC is primarily driven by the pressure gradient force (PG), of which the barotropic PG is dominant and offshore, while the baroclinic PG is onshore and increases with depth. The large baroclinic PG at depths, modulated by SW, that is, blended by tidal mixing, offsets the barotropic PG. Near the surface, the barotropic PG is nearly balanced by the Coriolis force, forming the geostrophic EMCC.