Satellite measured interannual variability of coastal phytoplankton pigment in the tropical and subtropical eastern Pacific

Interannual variability of phytoplankton biomass, measured as phytoplankton pigment concentrations (PPC) by the Coastal Zone Color Scanner (CZCS), was compared for eight selected, productive areas along the Pacific coast of Central America, Mexico, and California for 1980–1986. Monthly anomalies series were analyzed by means of principal components analysis (PCA) followed by varimax rotation, to identify spatially coherent variability between areas as indicative of El Niño forcing. PPC decreased during the 1982–1983 El Niño in all areas; however, there were regional differences in variability between the southern (tropical) areas and the northern (subtropical). In the southern areas the decrease occurred during 1982, but for the northern areas this was not observed until mid-1983. Results suggest the recovery of phytoplankton to pre-El Niño was larger and occurred earlier in the south as compared to the north. The same analysis was used for comparing sea surface temperature and sea level height series from the same areas, resulting in regional differences that were related to the two regional modes of chlorophyll variability. These were also investigated in relation to wind-driven upwelling (WDU). Unlike the other physical variables, upwelling showed little coherent variability between areas and was not clearly related to the major interannual changes of phytoplankton biomass during the period.