On the currents over the shelf off cap blanc in the northwest African upwelling area

An interpretation of current measurements yields, as a typical feature of the cross-component over the upper slope, two circulation cells with opposite rotation. Here coastal upwelling has been assumed to be mainly a two-dimensional phenomenon. Over the upper continental slope the core of the subsurface onshore return flow (∼+10 cm s−1) occurs at intermediate depths of 60 m to 70 m and above the bottom over the shelf. This flow causes a convergence just beneath the actual relatively shallow upwelling layer. A great part of the water masses of the return flow feeds the Ekman flux in the surface layer. Another minor part, however, sinks down the slope contributing to a weak offshore component above the bottom. It is suggested that the strength, the thickness and the depth of the onshore compensation flow increase with the intensity of upwelling.