THE 1982-1984 EL-NINO IN THE GULF-OF-CALIFORNIA AS SEEN IN COASTAL ZONE COLOR SCANNER IMAGERY

The 1982-1984 El Nino 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 concentration s ([Chl]) and phytoplankton productivity (PP) are not clear. The liter ature reports low [Chl] and PP for the mouth region and high values fo r 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 mo nthly composites of coastal zone color scanner (CZCS) satellite imager y, we generated time series for 33 locations throughout the gulf. We c alculated pigment concentration anomalies and derived a relative power index that provides a measure of the relationship between negative an omalies and El Nino episodes. Our analyses show that during 1978-1986, variability in phytoplankton biomass in the Gulf of California was no t dominated by El Nino events. Rather, strong tidal mixing and upwelli ng in the interior of the gulf masked the effect of El Nino 1982-1984 that otherwise showed so clearly in other coastal ecosystems of the ea stern 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 ei ther a weak effect or no effect of El Nino. Ballenas Channel showed an exceptional behavior, with an increase of pigment concentrations towa rd the end of 1983. Despite the Ballenas Channel having the highest su rface nutrient concentrations, pigment maxima there are not in general the highest of the gulf. The excess vertical turbulence in the channe l leads to light limitation of phytoplankton. Reduced mixing at the en d of 1983 promoted the increase of phytoplankton biomass in Ballenas C hannel. Strong non-El Nino conditions in 1984 caused lower phytoplankt on biomass in Ballenas Channel than during other years of the period a nalyzed.