Monthly composite images from the global coastal zone color scanner (CZCS) data set are used to provide an initial illustration and comparison of seasonal and interannual variability of phytoplankton pigment concentration along the western coasts of South and North America in the Peru Current system (PCS) and California Current system (CCS). The analysis utilizes the entire time series of available data (November 1978 to June 1986) to form a mean annual cycle and an index of interannual variability for a series of both latitudinal and cross-shelf regions within each current system. Within 100 km of the coast, the strongest seasonal cycles in the CCS are in two regions, one between 34¿ and 45 ¿N and the second between 24¿ and 29 ¿N, each with maximum concentrations (>3.0 mg m-3) in May--June. Weaker seasonal variability is present north of 45 ¿N and in the Southern California Bight region (32 ¿N). Within the PCS, in the same 100-km-wide coastal region, highest (>45 ¿S) and lowest (1.5 mg m-3) during the austral spring, summer, and fall, matching that evident throughout the CCS. Between these regions, off northern and central Chile, the seasonal maximum occurs during July--August (austral winter), contrary to the influence of upwelling favorable winds. Within the CCS, the dominant feature of interannual variability in the 8-year time series is a strong negative concentration anomaly in 1983, an El Ni¿o year.

The relative value of this negative anomaly is strongest off central California and is followed by an even stronger negative anomaly in 1984 off Baja California. In the PCS, strong negative anomalies during the 1982--1983 El Ni¿o period are evident only off the Peruvian coast and are evident there only in the regions 100 km or more from the coast. Although negative anomalies associated with the El Ni¿o were not present at higher latitudes (more than approximately 20 ¿S) in the PCS, the extremely sparse sampling weakens our confidence in the results of the interannual analysis in this region. An upper estimate of the systematic winter bias remaining in the global CZCS data after reprocessing with the multiple scattering algorithm is given in the appendix. ¿ American Geophysical Union 1994