Continental microseismic intensity delineates oceanic upwelling timing along the west coast of North America

Abstract

AbstractThe biological productivity of coastal upwelling regions undergoes marked interannual variability as marine ecosystems respond to changes in the prevailing winds. Determination of the principal metrics that define the upwelling cycle—the spring transition, when ocean conditions switch from downwelling‐ to upwelling‐favorable, and the Fall Transition, when conditions return to downwelling‐favorable—is essential for understanding changes in coastal productivity. Here we demonstrate that upwelling in the northern California Current System may be delineated by changes in microseismic activity recorded at a broadband seismological station in southwestern British Columbia. Observed high correlation between microseismic intensity and offshore bottom pressure fluctuations at ~0.2 Hz confirms a direct link to regional wind‐wave generation. Comparison of transition times derived from coincident 20 year records of microseismic intensity and alongshore wind stress for the British Columbia‐Oregon coast suggests that seismically derived times may be more representative of coastal upwelling than times derived using traditional methods.