A Review of the Temperature and Salinity Structures in the Approaches to Vancouver Island, British Columbia

Abstract

Oceanographic data gathered along the west coast of Vancouver Island since 1933 have been examined in an effort to derive an appreciation of oceanographic processes in this region.One area, which was the source of most data, was chosen as representative for the study, principally to satisfy continuity and partly to offset the tendency to use isolated sets of data as examples of "typical" coastal structure under rather general circumstances.The temperature and salinity structures and distributions are revealed as basically being functions of fresh water input, insolation, wind, and the ocean influence. The local climate is outlined, and some pertinent physical processes are reviewed, prior to a generalized description of the coastal oceanographic system.Predominant northwest winds and local runoff result in a shallow (20 to 40 m) springtime halocline in coastal waters. Summer insolation and the resulting stability of the thermocline, coincident with the halocline, limit the depth of mixing so that the summer runoff from mainland sources is mainly preserved in the shallow (10 to 20 m) upper zone of the salinity structure.Intermittent wind-induced divergence and an entrainment demand is offered as reason for the occurrence of cold, saline bottom water in this region during the summer.Autumnal cooling and southeasterly winds destroy the vertical structures and result in a near-shore accumulation of dilute surface water in winter. Relatively warm bottom temperatures offer evidence of a winter convergence, or relaxation of the divergence mechanism.Coastal oceanographic structures are often dominated by short-term variabilities. The significance of these is demonstrated by the ranges of variation obtained during time-series observations.