Hydrology and currents observed in the channel of Sardinia during the PRIMO-1 experiment from November 1993 to October 1994

The channel of Sardinia is one of the less-known areas of the Western Mediterranean sea. The paths of the Levantine Intermediate Water (LIW), the Tyrrhenian Dense Water (TDW) and the Western Mediterranean Deep Water (WMDW) mainly, in this wide passage, are still debated. Two major aims of the PRIMO-1 (Programme de Recherche International en Mediterranée Occidentale) experiment were to specify the mean circulation paths of these intermediate and deep waters there and to verify hypotheses about the migration of mesoscale eddies from Algeria to Sardinia and their effect on the circulation paths of all the water masses. Despite an important loss of moored instruments, current time series have been collected from November 1993 to October 1994 at four different locations and two CTD cross-sections have been performed. Current meters on the Sardinian slope indicate, during 1 year, an almost permanent alongslope flow toward the northwest in the intermediate and deep layers. Currents recorded on the African slope are always directed alongslope eastward down to 2500 m. Coherently, in the mid-western part of the channel, the bottom flow is northward along the isobaths, while the 200-m flow is southward due to the influence of anticyclonic eddies. At the bottom in the central part of the channel, the current is low and changing: episodes of northeast current along the orientation of the deepest channel axis alternate with westward flows. No seasonal variations have been clearly detected, but the mesoscale variability is large and has a deep signature in the western part of the channel.