Structure and seasonal characteristics of the Gaspe Current

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Abstract
CTD and current meter data from the northwestern Gulf of St. Lawrence were analyzed to study the structure and variability of the Gaspé Current. Since the current is buoyancy driven, its properties are strongly influenced by the seasonal variation of the freshwater discharge from the St. Lawrence estuary. From June to November, maximum speed decreases from 110 cm s−1 to 60 cm s−1. High vertical shears exist in the upper 40 m of the water column. During the same period, the width of the current decreases, and the position of the current maximum shifts from near the shore to about 14 km from the shore. These changes in the structure can be understood in terms of geostrophy and baroclinic deformation radius. In the temperature/salinity field the most prominent change from June to November is the continuing increase of surface salinity. Temperature change occurs mainly in the September‐November period, when atmospheric cooling accelerates. The effect of atmospheric cooling is also reflected in the density distribution, with the result that in November currents in the upper 30 m are seaward in the entire section (from Sept‐Iles to Marthe de Gaspé), while in the summer months the currents are seaward in the southern part and westward in the northern part of the section. Momentum balance of the current system is also investigated. It was found that east of Pointe‐des‐Monts, geostrophic balance is maintained, while west of Pointe‐des‐Monts the observations do not seem to be consistent with the assumption of geostrophy.