Satellite‐measured chlorophyll and temperature variability off northern Chile during the 1996–1998 La Niña and El Niño

Time series of satellite measurements are used to describe patterns of surface temperature and chlorophyll associated with the 1996 cold La Niña phase and the 1997–1998 warm El Niño phase of the El Niño‐Southern Oscillation cycle in the upwelling region off northern Chile. Surface temperature data are available through the entire study period. Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) data first became available in September 1997 during a relaxation in El Niño conditions identified by in situ hydrographic data. Over the time period of coincident satellite data, chlorophyll patterns closely track surface temperature patterns. Increases both in nearshore chlorophyll concentration and in cross‐shelf extension of elevated concentrations are associated with decreased coastal temperatures during both the relaxation in El Niño conditions in September‐November 1997 and the recovery from El Niño conditions after March 1998. Between these two periods during austral summer (December 1997 to March 1998) and maximum El Niño temperature anomalies, temperature patterns normally associated with upwelling were absent and chlorophyll concentrations were minimal. Cross‐shelf chlorophyll distributions appear to be modulated by surface temperature frontal zones and are positively correlated with a satellite‐derived upwelling index. Frontal zone patterns and the upwelling index in 1996 imply an austral summer nearshore chlorophyll maximum, consistent with SeaWiFS data from 1998–1999, after the El Niño. SeaWiFS retrievals in the data set used here are higher than in situ measurements by a factor of 2–4; however, consistency in the offset suggests relative patterns are valid.