Oceanographic Characteristics of Inlets of Vancouver Island, British Columbia

Abstract

Observations of temperature, salinity and dissolved oxygen content in all but one of the inlets of ten or more miles in length along the west coast of Vancouver Island were made by the University of British Columbia in 1959 and some additional observations were made in 1960 and 1961. The data are summarized to provide a general picture of the oceanographic characteristics of fifteen inlets. Attention is drawn to various features, and comparisons are made with the previous data which are available for only five of the inlets here described. Comparisons are also made with inlets in the mainland coast of British Columbia previously described by Pickard in 1961 in the Journal of the Fisheries Research Board of Canada.Generally the Vancouver Island inlets are shorter and shallower than those of the mainland coast and have shallower sills. The river runoff into the inlets is considerably less than into the mainland ones and has a winter maximum in contrast to the summer maximum on the mainland.Surface salinities during the summer in 1959, 1960 and 1961 were in most cases between 12 and 28‰ at the inlet head increasing to 27–31‰ at the mouth, while surface temperatures were between 10 and 15 °C. The low-salinity surface layer had a thickness of 2 m or less in all but two cases. Secchi disc depths were usually from 4 to 8 m. The deep water characteristics were from 7.5 to 9.5 °C and 31 to 33.6‰ except in the Clayoquot Sound group where the water was warmer (to 15.4 °C) and less saline (to 24.8‰). Dissolved oxygen values were very variable even along individual inlets. At depths greater than 100 m the content was usually less than 4 ml/l and in many cases less than 1 ml/l. The effect of the shallow sills in limiting deep water circulation appeared to be significant.Even when all the available data are assembled there are no time series of observations sufficient to prepare a description of seasonal variations of water properties, but data for six years from 1939 to 1961 are available for Alberni Inlet and for three years for the Nootka Sound inlets and for Neroutsos Inlet. These data indicate that in the deep water changes of up to 0.4‰ in salinity, 1 °C in temperature and 2.5 ml/l in dissolved oxygen content may occur from year to year.An hypothesis is advanced that, on account of the relatively shallow sills of many of the inlets, the deep water in their basins forms a 'memory' of extreme (high density) conditions of the continental shelf waters outside the inlets, and that the consistency of the basin water characteristics in the inlets suggests that the water properties observed in the shelf waters in 1959–61 by the Pacific Oceanographic Group may be typical of shelf waters in this region over many years.