A separated jet and coastal counterflow during upwelling relaxation off Cape São Vicente (Iberian Peninsula)

Abstract

The circulation and structure of the coastal upper ocean during the relaxation after an upwelling event around Cape São Vicente, the southwestern tip of Iberian Peninsula, are described. Hydrographic, ADCP, wind, and remotely sensed SST data during the upwelling season reflect the interplay of two contrasting regimes in the region: coastal upwelling and a nearshore countercurrent. The observations revealed a 40 km wide jet-like flow, separated from the coast, that advected cold water southward off the west coast and eastward around the Cape. It originated prior to the cruise in the upwelling that occurred off the prominent west coast capes, north of the sampling region. Adjacent to the coast, a narrow inshore counterflow advected warm water westward along the south coast, curled anticyclonically around the Cape with velocities up to 0.4 m s−1, and progressed poleward inshore of the previously upwelled water. The cold equatorward jet interacted with offshore waters and inshore countercurrent by generating small-scale instabilities, and weakened as it proceeded south and around the Cape. The inshore countercurrent was suppressed during the final part of the survey by an eastward flow associated with a return to an upwelling favourable wind off the south coast of Portugal.