Spatial and temporal variation in hydrography, chlorophyll, and oxygen of San Juan Channel: effects of local and external factors

Abstract

Situated between the Strait of Juan de Fuca and the Strait of Georgia, the San Juan Channel exists as a complex, dynamic, highly productive estuarine ecosystem—receiving oceanic input from the south and freshwater input from the north, respectively. Phytoplankton are highly important to marine ecosystems and studying the interactions between these organisms and the changing physical oceanographic environment is becoming increasingly important—especially in regions of high biological productivity such as the San Juan Channel. Stemming from the decided importance of these interactions, the purpose of this study was to build on our understanding of patterns and drivers of variation in the physical oceanography of the region—with a specific focus on oxygen and chlorophyll. We utilized measurements of temperature, salinity, density, chlorophyll fluorescence, and dissolved oxygen over the water column to assess variation both within fall 2012 and among fall data from 2004 to 2012. Correlations between density, chlorophyll, and oxygen were observed during fall 2012 and oceanic intrusions were seen as far as the north station—prior to the fall transition such intrusions were hypoxic and, presumably, had high CO2 concentrations as well. An observed correlation proposed in 2011 and verified with these data between pycnocline variation and tidal height allows for the quantification of such intrusions. Comparison of the interannual data displayed unprecedentedly high levels of chlorophyll and dissolved oxygen, found during fall 2012. Analysis of the full data set revealed covariance of some variables, such as deep oxygen and temperature, as well as the influence of potential driving factors, such as tides, oceanic input, and Fraser River flow, on the pattern of interannual variation.