The 1982–1984 El Niño in the Gulf of California as seen in coastal zone color scanner imagery

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The 1982–1984 El Niño was well documented for the Gulf of California, primarily with sea level anomalies. However, owing to strong tidal and atmospheric forcing, the general effects on chlorophyll concentrations ([Chl]) and phytoplankton productivity (PP) are not clear. The literature reports low [Chl] and PP for the mouth region and high values for both variables in the central gulf and in the region of the midrift islands. No data were collected in situ in the northern gulf. Using monthly composites of coastal zone color scanner (CZCS) satellite imagery, we generated time series for 33 locations throughout the gulf. We calculated pigment concentration anomalies and derived a relative power index that provides a measure of the relationship between negative anomalies and El Niño episodes. Our analyses show that during 1978–1986, variability in phytoplankton biomass in the Gulf of California was not dominated by El Niño events. Rather, strong tidal mixing and upwelling in the interior of the gulf masked the effect of El Niño 1982–1984 that otherwise showed so clearly in other coastal ecosystems of the eastern Pacific. Lower pigment concentrations were in fact detected with the CZCS at and near the entrance of the gulf, where vertical mixing is not as strong. Locations in the central and northern gulf showed either a weak effect or no effect of El Niño. Ballenas Channel showed an exceptional behavior, with an increase of pigment concentrations toward the end of 1983. Despite the Ballenas Channel having the highest surface nutrient concentrations, pigment maxima there are not in general the highest of the gulf. The excess vertical turbulence in the channel leads to light limitation of phytoplankton. Reduced mixing at the end of 1983 promoted the increase of phytoplankton biomass in Ballenas Channel. Strong non‐El Niño conditions in 1984 caused lower phytoplankton biomass in Ballenas Channel than during other years of the period analyzed.