Resumen del producto

Seasonal variability of the oceanographic conditions on the Pacific continental shelf of the southern part of the Baja California peninsula was analyzed using both historical data and field observations. Averaged monthly sea surface temperature (SST), obtained from the Advanced Very High Resolution Radiometer satellite images (AVHRR), showed the evolution of a thermal front between tropical and subtropical waters recorded during the transition period from winter-spring to summer-autumn. This evolution was characterized by a change in the direction of the SST horizontal gradient. The seasonal patterns of geostrophic currents calculated using hydrographic-altimeter data indicated that the SST seasonal variability was modulated by a pole-ward coastal flow during autumn that transported subtropical waters along the west coast of the peninsula. This intrusion was more intense during the El Niño years. Geostrophic balance in the study area presented meanders and eddies along the peninsula coast. In spring a relatively week meanders were located close to the coast. In summer the generation of the geostrophic eddies was intensified, and in autumn eddies were moved offshore. Another key feature observed in the mean seasonal values of the SST was a coastal upwelling activity that was more intense during the spring-summer period. The thermohaline structure, observed from the data obtained in-situ at the area, showed that the negative anomalies of SST (–2.5 °C) contrasted strongly with conditions recorded offshore. The combination of both the upwelling events and the tidal horizontal transport could be considered as an important nutrient flux mechanism for coastal lagoons.

Palabras clave: estructura termohalina; corrientes geostroficas; Magdalena

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