A. Miguel P. Santos

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

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.

Surface circulation in the Gulf of Cadiz: 2. Inflow-outflow coupling and the Gulf of Cadiz slope current

[1] A study of the upper slope circulation in the Gulf of Cadiz is presented. Observations, both original and revisited, and realistic numerical modeling are used together to describe the structure and variability of the slope current system above the Mediterranean outflow. It is shown that the Mediterranean inflow-outflow coupling plays a stronger role than that of the atmospheric forcing in driving the upper slope currents. The Mediteranean outflow forces a surface open ocean current toward the Strait of Gibraltar. Part of it is entrained into the outflow and the remaining flows into the Mediterranean. This latter component does not suffice for the observed transport of the Atlantic inflow into the Mediterranean. A secondary contribution to the inflow is therefore needed to complement the transport. This contribution comes from a persistent equatorward current along the upper slope between Cape St. Vincent and the Strait of Gibraltar. The jet is 20–30 km wide and significant in the upper 200 m attaining subinertial maxima as much as 0.3–0.4 m/s and monthly means in the order of 0.1–0.15 m/s. This current shows a strong variability at time scales in the order of 2–8 days, and displays a significant vertical shear. The response of the upper slope current to synoptic and seasonal atmospheric variability is analyzed. Very low correlation was detected at synoptic scales and the response of the system to seasonal forcing is unclear. A cycle of intensification in June–July and a decrease in winter is apparent in the measurements, but is weak in the model results. It is speculated that the cycle in the observed currents is associated with variability in the inflow/outflow coupling system, rather than driven by seasonally changing wind forcing.