Five years (1997–2002) of northern California Current SeaWiFS ocean color data place cold, low salinity hydrographic anomalies observed in summer 2002 into a larger spatial/temporal context and present their biological ramifications. Monthly mean chlorophyll concentrations were >1.0 mg m⁻³ larger than the previous 3 year average over the entire shelf from British Columbia (BC) to northern California (CA) in 2001–2002, spatially most extensive over the BC and Washington (WA) shelves but strongest (>2.0 mg m⁻³) on the southern Oregon shelf. Positive anomalies develop in August 2001 off BC and October 2001 off WA. By October 2002, shelf anomalies are reduced. Offshore, spatially extensive anomalies develop off CA (36°–42°N) in fall 2002, disappearing by December. Concurrent altimeter data show over 1000km of equatorward displacement. The positive chlorophyll anomalies, their spatial patterns and displacement are consistent with advection of subarctic, nutrient-enriched water into the California Current.