Handbook of Physical, Chemical, Phytoplankton, and Zooplankton Data from Hecate Strait, Dixon Entrance, Goose Island Bank and Queen Charlotte Sound

Abstract

This report summarizes physical and lower trophic level data collected in Hecate Strait and Queen Charlotte Sound. The purpose is to: 1) organize those portions of the physical, water chemistry, phytoplankton, and zooplankton data base which will be required for the development of lower trophic level simulation models for Hecate Strait, 2) summarize appropriate lower trophic level data (physical, water chemistry, phytoplankton, and zooplankton) to produce best estimates of interannual and decadal seasonal patterns, and 3) quantify the extent of spatial variability that may exist within the Hecate Strait Region. The report is laid out in four sections: 1) physical climatic and oceanographic factors, 2) nutrients, 3) chlorophyll and primary production, and 4) zooplankton. There was considerable between-site variability in precipitation (wetter along the mainland coast); sunlight (more hours of bright sunlight in southern Queen Charlotte Sound and northwestern Hecate Strait); sea surface temperatures (cooler near Queen Charlotte Strait); and sea surface salinity (fresher near the mainland coast). There were also some striking long-term trends and low frequency oscillations in physical conditions. In general, the data suggest that global warming has significantly increased winter and spring temperatures, but not summer or fall temperatures in the region. There were no between-site (Dixon Entrance, Hecate Strait, and Queen Charlotte Sound) differences in nutrient concentrations. During the summer, the depth of the upper windmixed layer varied between 10 to 30 m, and summer concentrations of NO3 , PO4 and SiO2 were low between 0-5 m, about doubled between 5-15 m and then gradually increased with water depth. Winter concentrations were higher than in the summer. Chlorophyll a concentrations measured from surface waters (<10 m deep) at three locations (Dixon Entrance, Hecate Strait, and Queen Charlotte Sound) were similar between years and between sites. During the summer, surface (0-20 m) chlorophyll a concentrations averaged about 2 µg·L-1, increased significantly between 20-30 m and decreased below 30-40 m. During the winter, chlorophyll a concentrations were consistently much lower. Zooplankton biomasses from Hecate Strait and Queen Charlotte Sound were statistically similar and higher than from Dixon Entrance. Long-term time trends for the years 1957-2001 suggested that some of the variability in zooplankton biomass may have been related to the periodicity of ENSO events. Short-term time trends for the 11-year period 1991-2001, suggested that zooplankton biomasses were low during the early 1990s, then increased substantially during the mid- 1990s and declined during the late 1990s. These patterns were only weakly related to the ENSO events of 1992 and 1998. Biomass trends developed slowly and lasted longer than would be expected if it was driven by ENSO events alone. The implication is that trends in zooplankton biomass are driven by complex biologically and physically mediated events which may or may not be related to ENSO.