Biological and Hydrographical Evidence for Pacific Equatorial Water on the Continental Shelf North of Vancouver Island, British Columbia

Abstract

Data from two cruises in April and November 1977 indicate the presence of Pacific equatorial water on the continental shelf north of Vancouver Island. Water with the general temperature/salinity characteristics of the California Undercurrent was found on the shelf at both times. Equatorial water formed ~30% of this deep-water mass, with Pacific subarctic water making up the remainder. Evidence for the presence of equatorial water was supported by the occurrence in the study area of six normally subtropical zooplankton species: Mesocalanus tenuicornis, Lophothrix frontalis, Candacia bipinnata, Lucicutia flavicornis, Heterostylites longicornis, and Pleuromamma xiphias. An increase in the proportion of equatorial water on the shelf, and a concomitant extension of the limits of distribution of oceanic zooplankters in the study area, both infer an intrustion of deep water onto the shelf during the period between the two cruises. This intrusion is probably a regular event with important ramifications for the zooplankton and fish communities of the area.Key words: continental shelf, British Columbia, hydrography, California Undercurrent, zooplankton