Circulation in the French mediterranean coastal zone near Marseilles: the influence of wind and the Northern Current

Abstract

Current meters were moored for a year both in and beyond the Cassis Bay to study the dispersion of muds discharged at a depth of ∼300 m, through a pipe, a few km from the coast and at the head of a submarine canyon. The east–west orientation of the coastline and a marked orography constrain the major winds to easterlies or westerlies. Empirical orthogonal function analysis shows that both wind regimes create a significant down-wind circulation, with the latter inducing also intense upwelling. Characteristics of the Northern Current, which flows along the slope, have been defined using a fine-grid hydrological survey. A narrow continental shelf allows the Northern Current to reach often the coastal zone in the study area; thus, the overall water circulation in the embayment is westward. In winter, this current develops steep mesoscale meanders and penetrates easily through the canyon, into the bay. Hence, although the coastal circulation near Marseilles is partly down-wind, it is dependent mainly on the Northern Current (on both general and meso-scales). The mesoscale variability cannot be predicted without monitoring the Northern Current itself.