PHYSICAL OCEANOGRAPHY OF THE WESTERN CANADIAN CONTINENTAL-SHELF

All regions of the Canadian west coast feel the influence of strong southeast storm winds in autumn and winter, Maximum wind speeds, currents and wave heights occur in late autumn and winter, with an abrupt transition in October/November marking the change from summer to winter regimes. In summer, surface circulation in all shelf regions is strongly influenced by buoyancy flux and by topographically controlled eddies, but in winter the flow. is generally down wind. The cycle of southeast winds in winter and northwest winds in summer creates interesting annual signals. In Hecate Strait, bottom water in the central gully is warmest in winter, due to downwelling and mixing of surface waters by southeast winds. On the southern Vancouver Island shelf, lowest oxygen concentrations in bottom water are found in summer due to upwelling through Juan de Fuca Canyon and along the shelf break. Concentrations of nutrients in this upwelled water are high. Local tidal mixing does not appear to be sufficiently strong to bring these nutrients to the surface on the shelf, but instead, tidal currents in the Juan de Fuca-Strait of Georgia system and coastal upwelling on the shelf mix these nutrients to the surface, and local currents carry the nutrients to mid-shelf. Upwelling persists along the entire coast of Vancouver Island in summer, with a strong shelf break current flowing to the southeast, counter to the poleward, buoyancy-driven Vancouver Island Coastal Current over the inner shelf. All exposed coasts are subjected to extreme waves in winter, but Dixon Entrance and Hecate Strait are protected to some extent by the Queen Charlotte Islands. Nevertheless, the waves and currents in winter in northwestern Hecate Strait and southeastern Dixon Entrance move the sediments to the northeast, building up Rose Spit and eroding the northeastern shore of the Queen Charlotte Islands.