Mixing and circulation in the northwestern Gulf of St. Lawrence: A study of a buoyancy‐driven current system

Abstract

Mixing and circulation near the entrance to the St. Lawrence estuary are studied by using the hydrographic and current meter data obtained in the summer of 1978. It is found that the currents in the upper 40 m are mainly buoyancy driven. As the low‐salinity water from the estuary flows eastward and encounters the more saline Gulf of St. Lawrence water, a wedge‐shaped layer of low‐salinity water and a density front are formed. Intense vertical mixing takes place along the boundary of the layer. The geostrophic current associated with the front flows southward and, upon reaching the shore, turns east. From there on it flows parallel to the coast and is reinforced by a basin‐wide cyclonic gyre forming a strong coastal jet, the Gaspe current. The salinity front divides the deep water into the two flow regimes. Eastward (westward) of the front the currents in the 40‐ to 100‐m depth are cyclonic (anticyclonic). The variability of the temperature and salinity fields is examined. The effect of the variability on the interpretation of the data is discussed.