Near-surface phytoplankton distribution in the western Intra-Americas Sea:The influence of El Nino and weather events

The space-rime variation of phytoplankton pigments in the western Intra-Ame ricas Sea (IAS), in the vicinity of the island of Cuba, is examined using d igital images obtained with the Coastal Zone Color Scanner sensor flown abo ard the Nimbus 7 satellite from 1978 to 1986. The results are compared to h istorical in situ hydrographic observations. A marked seasonality in pigmen t concentration was observed in waters around Cuba, with an average of 0.07 mg m(-3) in summer (April-September) and 0.13 mg m-3 during winter (Octobe r-March). The range of variation in pigment concentration was larger in the Gulf of Mexico relative to the western Caribbean Sea. We identified four b iogeographical areas on the basis of groups of pixels with similar patterns of time variability. These are area I: southwest of Cuba, Yucatan Channel, and Florida Strait; area II: central Gulf of Mexico; area III: east of Cub a; and area IV: central Caribbean Sea, south of Jamaica and Hispaniola. Two major meteorological events led to anomalies in the seasonal cycle of pigm ent concentrations. During El Nino-Southern Oscillation (ENSO) of 1982-1983 , positive anomalies were observed in the pigment concentration in the west ern IAS during winter months. This was associated with intense mixing of th e water column by higher-frequency and stronger winds associated with cold fronts. ENSO 1952-1983 therefore had a fertilizing effect on the IAS region . Another positive anomaly was observed in 1980-1981, a non-ENSO period tha t featured higher hurricane and extratropical low-pressure activity.