Winter Hydrography and Plankton Distribution on the Southern British Columbia Continental Shelf

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Abstract
The early winter (November–December 1983) concentrations and spatial distributions of chlorophyll and zooplankton on the southern British Columbia continental shelf are shown to be closely related to patterns of hydrographic parameters. Concentrations of both are an order of magnitude less than published summer values for the same area. On the basis of hydrographic and planktonic characteristics, the continental shelf region can be divided into an area dominated by the Vancouver Island Coastal Current and one dominated by the northward flowing Davidson Current which can be isolated in the data and traced along the outer shelf edge. Highest chlorophyll and zooplankton concentrations (1.0 mg∙m−1 and 2900 counts∙m−3) were found in Coastal Current water and the frontal zone between this and the Davidson Current water. The warmer Davidson Current water was associated with extremely low chlorophyll and zooplankton concentrations (−3 and −3). The spatial distributions of both chlorophyll and zooplankton reflected variations in the cross-shelf position of the Davidson Current which appeared to be topographically controlled. Contours of sea surface temperature, inferred from hydrographic data, were similar to contours of chlorophyll and zooplankton concentration. Both in situ temperature and plankton distributions were spatially consistent with thermal patterns in concurrent high-resolution satellite infrared imagery. Areas of increased surface thermal gradient were consistent with in situ measured biological fronts.