A 5-year time series of coastal zone color scanner imagery (1980--1983, 1986) is used to examine changes in the large-scale pattern of chlorophyll pigment concentration conincident with the spring transition in winds and currents along the west coast of North America. The data show strong interannual variability in the timing and spatial patterns of pigment concentration at the time of the transition event. In both 1980 and 1981 a large increase in pigment concentration occurs (from 0.5 mg m-3 to <3.0 mg m-3 in 1980 and from 0.3 mg m-3 to <1.5 mg m-3 in 1981). In these years, as well as in 1982, the increase takes place between ≈33¿N and ≈41¿N, but it occurs in a region centered 300 km offshore in 1980 and within 300 km of the coast in 1981 and 1982. These changes are in contrast to 1983 and 1986, when virtually no change in pattern or concentration is associated with the transition. Calculations of light availability and in situ data suggest this region is nutrient limited even in the mid to late winter. Time series of pigment concentration and wind forcing for extended periods before and after the transition date show that increases in concentration are associated with strong wind mixing events prior to the transition and with the onset of southward wind stress (upwelling) at the time of the transition. Interannual variability in the response of pigment concentration to the spring transition appears to be a function of spatial and temporal variability in vertical nutrient flux induced by wind mixing and/or the upwelling initiated at the time of the tranistion. Interannual differences in the mixing regime are illustrated with a one-dimensional mixing model. ¿ American Geophysical Union 1989