Water masses and circulation in the Western Alboran sea and in the Straits of Gibraltar

Abstract

Some new elements of Alboran Sea circulation and water masses in close connection with flows through the Straits of Gibraltar are presented. A general description is given of water masses found in 1981 during MEDIPROD IV cruise from the Gulf of Cadiz to the Gulf of Lions, followed by a brief review of the conditions found in the Straits of Gibraltar based on 1981 and 1961 observations. The hydrological structure (vertical and horizontal) and surface and bottom currents typical of the western Alboran Sea are analysed. We present some detailed observations about vertical currents in the deep waters near the Straits and finally we analyse the characteristics of the Mediterranean overflow through the Straits. Our conclusions in part confirm those of Bryden and Stommel (1982) and in part shed light on the general pattern of the Mediterranean currents entering the Alboran Sea from the east. However, considering the suggestion of Stommel, Bryden and Mangelsdorf (1973) that the deep currents in the interior of the western Mediterranean basin are basically controlled by a Bernoulli flow induced by the intense currents in the Straits and the weak vertical stratification in the Mediterranean, we suggest that an interaction of a large scale circulation pattern and the topography of the Alboran basin, which is much shallower than the western Mediterranean basin, may play a major role in controlling, hydraulically, the deep Mediterranean waters overflow. A detailed water mass analysis of 1981 data and comparison with previous data revealed a time and space variability in the Mediterranean waters. The scales of this variability are unknown but the θ- S variations make it difficult to make assumptions as to the depth of origin of the deep waters found in the Alboran sea which flow into the Atlantic Ocean over the Gibraltar sill.