The Effect of Stratification on the Tidal Circulation over the Scotian Shelf and the Gulf of St. Lawrence: A Numerical Study

A three-dimensional numerical shelf circulation model is used to examine the effect of the seasonal variation in water column stratification on the tidal circulation over the Scotian Shelf and the Gulf of St. Lawrence. The model is driven at its lateral open boundaries by tidal forcing expressed in terms of sea surface elevations and depth-averaged currents for five tidal constituents (M₂, N₂, S₂, K₁, and O₁). Three numerical experiments are conducted: the control run (including the full suite of forcings and dynamics), a barotropic run, and one that is similar to the control run but without the baroclinic pressure gradients. Each model run lasts one year and is preceded by a spin-up period of four months that is initialized with climatological hydrographic states. The focus of this study is on the semi-diurnal tide M₂, which is one of the dominant tidal constituents in this region. Comparison of model results in the three experiments suggests that the seasonal variation in stratification affects the M₂ tidal circulation along the shelf break and over the deep waters off the Scotian Shelf through its influence on the baroclinic pressure gradient, and affects the M₂ tidal circulation in Northumberland Strait (in the Gulf of St. Lawrence) through its influence on vertical mixing and bottom stress.