Satellite-measured chlorophyll and temperature variability off northern Chile during the 1996-1998 La Nina and El Nino

Time series of satellite measurements are used to describe patterns of surf ace temperature and chlorophyll associated with the 1996 cold La Nina phase and the 1997-1998 warm El Nino phase of the El Nino - 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-v iew Sensor (SeaWiFS) data first became available in September 1997 during a relaxation in El Nino conditions identified by in situ hydrographic data. Over the time period of coincident satellite data, chlorophyll patterns clo sely track surface temperature patterns. Increases both in nearshore chloro phyll concentration and in cross-shelf extension of elevated concentrations are associated with decreased coastal temperatures during both the relaxat ion in El Nino conditions in September-November 1997 and the recovery from EI Nino conditions after March 1998. Between these two periods during austr al summer (December 1997 to March 1998) and maximum El Nino temperature ano malies, temperature patterns normally associated with upwelling were absent and chlorophyll concentrations were minimal. Cross-shelf chlorophyll distr ibutions appear to be modulated by surface temperature frontal zones and ar e positively correlated with a satellite-derived upwelling index. Frontal z one patterns and the upwelling index in 1996 imply an austral summer nearsh ore chlorophyll maximum, consistent with SeaWiFS data from I 1998-1999, aft er the El Nino. SeaWiFS retrievals in the data set used here are higher tha n in situ measurements by a factor of 2-4; however, consistency in the offs et suggests relative patterns are valid.