Circulation, Variability, and Dynamics of the Scotian Shelf and Slope

Abstract

A brief summary of historical data relating to the mean circulation on the Scotian Shelf and Slope reveals the distribution of various water masses and certain general characteristics of the current field, supported by geostrophic calculations and observations of surface drift. However, extreme variability resulting from wind and tidal forces is evident in all measurements made on the shelf and slope. Various measurements and models of the first-order variable flows, including wind-driven circulation, diurnal and semidiurnal tides, and inertial waves, are also reviewed. Results from a new model for inertial motions in a variable-depth mixed layer are found to closely reproduce the transient behavior of inertial energy at the 50-m depth on the shelf, but certain aspects of the model are inconsistent with the observations. With results from a mooring program on the shelf in September–December 1968, the dynamics of the mean circulation are examined in the context of a vertically integrated, two-dimensional model. Reynolds stresses associated with the first-order flows are found to be insignificant in the inshore zone (within 90 km of the coast) where the balances are between mean wind and bottom stresses, surface pressure gradients, and Coriolis forces. Over the outer shelf, however, the geostrophic onshore balance breaks down and Reynolds stress divergences in the inertial and tidal bands become important. At the shelf break, generation of the baroclinic semidiurnal tide produces internal Reynolds stress forces comparable to the barotropic terms on the shelf. Key words: mean circulation, semidiurnal barotropic and internal tides, inertial waves, mixed layer, wind-driven circulation, Reynolds stress, geostrophic, Scotian Shelf