Oceanography of Saanich Inlet in Vancouver Island, British Columbia

Abstract

Saanich Inlet is a fjord (24 km long) having a submerged (75-m) sill at the entrance, behind which there is a deep (234-m) basin. The properties of the water have been observed from time to time from 1927 through 1960. The resulting data are reviewed to provide representative values and structures of temperature, salinity, density (σt), dissolved oxygen content and sound velocity for each month throughout the year. Above the sill depth the properties of the water are normal and continuous with those in the approaches which connect with the Strait of Georgia. The waters below the sill depth are isolated, oxygen-deficient, and usually contain hydrogen sulphide. There is considerable ambient variation in the structures because the currents are too weak to disperse or mix the locally generated concentrations.The runoff into the head of the inlet is negligible. The major source of fresh water is in the approaches. It intrudes the inlet and provides a weak estuarine flushing mechanism above the sill depth. The waters below the sill are flushed only when the water in the approaches becomes sufficiently dense to cascade over the sill into the deep basin.The sound-ranging conditions are far from ideal. From March through July there is a major sound channel at mid-depths above the sill. This vanishes in August and a sound divergence zone develops and persists until December. In addition, the ambient variations provide anomalous transmission conditions.During the autumn (September through November) high concentrations of fish have been observed at the sill depth, associated with the oxycline. Probably the fish are attracted to the area by very large concentrations of zooplankton (Euphausids) that have been observed there at the same time.