Fronts, jets, and counter-flows in the Western Iberian upwelling system

Abstract

The results of a fine resolution hydrology survey conducted off the northern Portuguese coast at the end of the upwelling season are presented. The most striking features were the upwelling front and the associated southward jet. Counter-flows were detected both over the slope and at the inner-shelf. The southward current is surface intensified with maximum values of about 40 cm s −1 and diverges to the south of the observed area recirculating both onshore and offshore. Along the slope, a warmer and saltier poleward current interacts with the jet generating an anticyclonic eddy about the Aveiro Canyon. Possible mechanisms of topographic forcing and filament development in the zone are discussed. Inshore, a coastal current advects warmer water northward creating a second front at the inner-shelf. The surface layers to the coastal side of the upwelling front are dominated by a low salinity lens, which we proposed to name the Western Iberia Buoyant Plume (WIBP). The equatorward flow, the coastal current and the stratification input of the WIBP introduce strong complexity into the dynamics of this double-frontal upwelling system. The plume is stirred being partially advected to the south and offshore while entrained in the upwelling jet. On the shore side, the plume is advected to the north by the coastal counter-flow. A conceptual model of circulation is presented.