Influence of the 1997-98 El Nino on the surface chlorophyll in the California Current

Satellite-derived time series for the California Current System (CCS) showe d marked changes in the surface chlorophyll a concentration (Chl, mg m(-3)) associated with the 1997-98 El Nino. In addition to the previously known d e crease in Chi off Southern California (Fiedler, 1984), we also observed a significant increase of Chi off Baja California. Whereas the extent of eut rophic (Chl > 1.0) areas decreased throughout the CCS, the extent of mesotr ophic areas (0.2 < Chi < 1.0) off Baja California approximately doubled. Th e reduced area of eutrophic waters is attributed to weakened upwelling but the increase in the offshore mesotrophic area off Baja may be caused by blo oms of nitrogen-fixing cyanobacteria. Using revised Coastal Zone Color Scan ner data we detected similar changes during the 1982-83 El Nino.