Seasonal and tidal effects on water density gradients in the San Juan Channel

Abstract

The San Juan Channel is one passageway linking the Strait of Georgia and the Strait of Juan de Fuca. Thus, the physical oceanography of this region is complex and has both estuarine and oceanic influences. We sampled a 5-station transect along the San Juan Channel during fall 2011 as part of a multi-annual study started in 2004 and a monthly study started in early 2011. We deployed a CTD to gather information on temperature, salinity, and density structure in the water column. Temperature followed an annual cycle with cooling in the winter and warming in the summer, while haloclines were more tidally modulated. Short-term along-channel density structure was controlled by both tides and wind. Density stratification increased at the south end increased during flood tides, and at the north end and mid-channel during ebb tides. The depth and width of the pycnocline at the southern end of the channel were correlated to tidal height. These findings enhance our understanding of both short-term and long-term patterns in density gradients of the San Juan Channel pelagic environment.