Antarctic Intermediate Water influence on Mediterranean Sea Water outflow

This study of the mixing of Mediterranean Sea Water (MW) with the surrounding waters was made possible by the Semane 2002 cruise (Sortie des Eaux Meditérranéennes dans l'Atlantique Nord-Est) that took place in the Gulf of Cadiz in July 2002. Potential temperature, salinity, oxygen, nutrients and CFC data are used to describe the water masses present in the Gulf. In the southern part of the basin, a water mass characterised by low oxygen, high nutrient and low CFC concentrations occurs along the African continental slope. This water has been identified as the modified Antarctic Intermediate Water (AAIW). It has been previously observed south of this section, at the latitude of the Canary Islands, as a northward flow between the African shelf and the islands. The modified AAIW found in the Gulf of Cadiz is situated at a density of 27.5 kg m −3. Above, at 27.3 kg m −3, the lower limb of the North Atlantic Central Water is observed as a salinity minimum. The modified AAIW enters the Gulf of Cadiz along the south-western part of the continental shelf. It flows cyclonically and exits north-westward. In the northern part of the gulf, due to the presence of the Mediterranean Undercurrent (MU), the AAIW flows off the coast. An optimum multiparameter analysis was conducted to evaluate the influence of the AAIW on the MW northwest of the basin. We show that the AAIW is present in the lower core of the MU at a proportion of 12.9±8.2% and is absent in the upper core. ► The presence of AAIW is outlined in the Gulf of Cadiz from CFC and oxygen minima and a nutrient maximum. ► AAIW enters the southwestern part of the Gulf of Cadiz along the continental shelf and spreads cyclonically. ► Proportions of MW, NACW and AAIW in the upper and lower cores of the Mediterranean undercurrent are calculated through an OMP analysis. ► AAIW is present in the lower core of the Mediterranean undercurrent at a proportion of 12.9%.