The inlets of the British Columbia mainland coast are morphologically fjords but few possess sills of depth less than 15 m.The most significant influence in them is the fresh water runoff, chiefly from rivers. It is large in many of the inlets fed by rivers from glaciers, is seasonal in flow, and determines the estuarine character and circulation of the inlets and thereby the distribution of water characteristics.In the large-runoff inlets the surface salinity increases from zero at the head to coastal sea values at the mouth. In winter the surface temperature is low and uniform but in summer it increases from the head, reaches a maximum where the salinity is about 8‰ and then diminishes toward the mouth. The water is highly stratified, particularly from the surface to about 20 m depth where the salinity rises to 90% or more of the deep water value. The marked halocline in the upper layer is accompanied by a marked thermocline. Below 50 m the salinity and temperature do not change much along the length of an individual inlet.There is a pronounced geographical change of deep water characteristics from 30.7‰ and 8.3 °C in the southern to 33.2‰, and 6.3 °C in the northern inlets. In general, seasonal changes of temperature can be detected to 100 m but of salinity to only 30 m, suggesting a difference in the rates of eddy diffusion. Changes of deep water characteristics occur irregularly.In many of the inlets a temperature minimum at 20 to 100 m depth is common in the inner reaches in the spring and diminishes in intensity later in the year.In the inlets with medium or small runoff the surface salinity is generally higher and changes less along an inlet, and the halocline and thermocline are less marked. The homogeneous surface layer characteristic of the large-runoff inlets is usually absent.Generally the large-runoff inlets show less variable dissolved oxygen values along an inlet at any depth than do the small-runoff inlets. Supersaturation of the upper layers is common, and there is often an oxygen maximum just below the halocline of the larger-runoff inlets. A few small-runoff inlets have a mid-depth oxygen minimum in which the lowest values are at the inlet head. Dissolved oxygen values of less than 2 ml/l are not common in any mainland inlets and zero values have not been definitely recorded.The optical turbidity in large-runoff inlets is high in the surface layer, lower in the main body of water, and often increases in the bottom 50 to 100 m. At the heads of the large-runoff inlets Secchi-disc depths of 0.1 to 0.3 m are common in the summer. In the inlets with smaller runoff the turbidity is less. In both types the turbidity is at a maximum in the summer and a minimum in the winter, and the particulate material in the water is largely minerogenic.Internal waves of period 1 to 4 minutes and amplitude up to 5 m occur in the upper layers. At mid-depth (20 to 150 m), vertical oscillations of the isotherms with semidiurnal tidal period are common, the amplitude being from 5 to 75 m.A waxy substance sometimes found floating or washed ashore in Bute Inlet during cold winters appears to be peculiar to that inlet as no reference has been found to any similar substance being observed elsewhere in the world.
Mapping sensitive benthic habitats in the Strait of Georgia, coastal British Columbia: deep-water sponge and coral reefs