Satellite analysis of the Juan de Fuca Eddy, a persistent oceanic feature in the Pacific Northwest

Results of the ECOHAB PNW project suggest that a persistent oceanic feature, the Juan de Fuca eddy, is a source for harmful algal blooms in Pacific Northwest coastal waters. Here we present the eddy's characteristics as observed by satellite data. In sea surface temperature (SST) and chlorophyll-a (chl), the eddy is a cold, high-chl feature that is present during the upwelling season (spring through fall). Compared to the adjacent coastal shelves, the eddy interior is weaker in seasonal variability and its maximum chl occurs earlier, in late spring rather than early fall. Over the upwelling season, the eddy grows cross-shore from ~50-100 km. As it grows, the eddy is bounded by a strong offshore front where local chl maxima are found, in contrast with low chl values in the eddy interior. During the strong El Niño of 1997–1998, the cross-shore contrast between eddy and offshore SST weakened and fewer realizations of the eddy were observed in the satellite data.