Deep and intermediate water replacement in the Strait of Georgia

Abstract

We have studied deep‐water replacement processes in the Strait of Georgia using data from two different observational programs. From the monthly hydrographic data of Crean and Ages (1971) we have recognized the propagation of cold, brackish and well oxygenated waters northwards from Boundary Passage at depths between 75 and 200 m. We found a significant correlation over the years 1967–78 between surface cooling and temperature drops at those depths some months later. Measurements at an array of moorings in the central Strait of Georgia (Stacey et al., 1987) revealed the presence during summer months of currents concentrated near the bottom and varying with fortnightly and monthly periods. We have interpreted this phenomenon in terms of gravity currents originating from Boundary Passage during periods of neap tides and introducing at depth salty waters from the Strait of Juan de Fuca. Our analysis confirms in part the validity of the deep‐water replacement mechanisms advanced by Waldichuk; however, we find that wintertime replacement does not usually reach bottom while summertime penetration of waters from the Strait of Juan de Fuca clearly does. Because of the important role played by tidal mixing, monthly sampling is inadequate to resolve and understand the deep‐water replacement processes.