Research Document - 2001/113

Physical oceanography of Southern Gulf of St. Lawrence and Sydney Bight Areas of Coastal Cape Breton

By Joël Chassé

Abstract

This document describes some aspects of the physical oceanography of the Southern Gulf of St. Lawrence and Sydney Bight areas of coastal Cape Breton (Fig. 1.). The description is based on previously published information complemented with results from a three-dimensional numerical model of the ocean developed at Bedford Institute of Oceanography. The water column in the Cape Breton Trough is strongly stratified in summer, which isolates cold water (0 - 3 ?C) at the bottom. Surface water temperature in summer is between 16-18 ?C and the thermocline is sharply defined between 20-40m depth. In Sydney Bight, the maximum stratification is deeper in the water column (30-50 m). The semi-enclosed shape of the Gulf of St. Lawrence favors the formation of a northeastward coastal current, along the west coast of Cape Breton, that is modulated and can be reversed by the action of tide and wind. There are indications that this flow, combined with the morphology of the Cape Breton Channel and the tidal action, generates a pumping mechanism that brings deeper water closer to the surface layer. On a smaller scale, the Cape Breton Trough and Sydney Bight influence the current patterns creating gyres and upwelling. Wind can be an important determinant of the direction and speed of surface water movement. There is a surface outflow within Cabot Strait along the Cape Breton coast that is partly counterbalanced by an inflow in the deep Laurentian Channel. The presence of a clockwise gyre in Sydney Bight could be linked with the outflow at Cabot Strait and the morphology of the Bight itself. Sydney Bight and the west coast of Cape Breton have ice present for 60 to 100 days per year on average, from January to the beginning of April.

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