Stark Physical and Biogeochemical Differences and Implications for Ecosystem Stressors in the Northeast Pacific Coastal Ocean

Abstract

AbstractRegional differences in water properties and responses to stressors are key to understanding ecosystem vulnerabilities in coastal regions globally. Our study focuses on Canada's British Columbia coastal waters, from Queen Charlotte Strait to the Strait of Georgia. This area is bisected by shallow, narrow, tidally mixed channels with some of the strongest tidal currents in the world. We examine differences between regions on either side of this constriction, focusing on physical water properties and responses to three potential physical and biogeochemical stressors: nutrient levels, marine heatwaves, and ocean acidification. Our results quantify a spatially abrupt and temporally persistent lateral gradient in temperature, salinity, and density co‐located with a previously documented strong mixing zone. The distributions of density on either side of this front remain largely distinct throughout the tidal cycle, for all seasons, and for over 70 individual years for which data are available. Additionally, nutrient concentrations and molar ratios north of the front are statistically distinct from those to the south, and regions north of the front responded more strongly to the arrival of the marine heatwave known as “The Blob”. Lastly, regional differences in sensitivity to ocean acidification are identified, with high values at the surface in the Discovery Islands making that area very sensitive to ocean acidification. These results demonstrate the degree to which dramatic water property differences in adjacent coastal regions can persist over a wide range of time scales, with important connections to their responses to environmental stressors and implications for present and future ecosystem vulnerability.