REVIEW OF THE OCEANOGRAPHIC, CHEMICAL AND PLANKTOLOGICAL ASPECTS OF THE VALPARAISO BAY AND ADYACENTS AREAS

Abstract

The Valparaíso región, for which this review paper was prepared, is located in a températe zone characterized mainlv by aestival (November to March) and a wintery (May lo September) seasons. S and SW winds are predominant with its highest frequeney in spring. The combined effeets of the upwelling caused by these winds and the advection of colder subantarctic waters carried into the región by the Humboldt Current keeps the annual airand water mean temperature relatively low. Upwelling of the rich micronutrient Subsurface Equatorial water, fertilizes the photic layer in the Coastal zone causing favorable conditions for an intense phytoplankton proliferation. The annual phytoplankton máximum shows several major pulses, reaching its highest abundance in the springsummertime and at the beginning of autumn. These blooms offer an abundant íbod availability, for planktophagous organisms. The sumnier seasonal thermocline causes a stratificación in the water column. I f this thermocline is not destroyed by strong S and SW winds and reinains for long periods of time, the nutrients will be depleted drastically causing a decay in the phytoplankton abundance and an acceleration in the populación succession. The surface salinity is diluted in winter by rain, and in summer by che increase in freshwacer effluents caused by the thawing of the ice from the Andes cordillera. This freshwater is carried into the ocean by the Aconcagua River causing also an imponant increase in silicate concentration in the surrounding of its mouth.