Characteristics and circulation of the surface and intermediate water masses off Algeria

Abstract

During the Médiprod-5 experiment, conducted off Algeria between ∼ 0 and 5°E in 1986–1987, ∼100 CTD casts were made in May–June 1986 down to ∼ 800 decibars. Their analysis is supported by results from current meters set in place for ∼ 9 months in the same area. The flow of Modified Atlantic Water (MAW) off Algeria, namely the Algerian Current, was initially (near 0–2°E) structured as a narrow (∼ 30 km) and deep (∼ 400 m) coastal vein (transport ∼ 1.7 Sv). It became wider and thinner to the east, with its core slightly detached from the coast. This current was first expected to generate coastal anticyclonic eddies and second to interact strongly with open sea anticyclonic eddies. Two such mesoscale eddies were sampled. Geostrophic calculations and drifting buoy trajectories clearly show that the whole Algerian Current was deflected seawards due to interaction with an open sea eddy. Spatial gradients of the temperature minimum of the Winter Intermediate Water (WIW), and of the temperature and salinity maxima of the Levantine Intermediate Water (LIW), are consistent with historical data. They indicate that both waters flow eastwards along the Algerian continental slope. These data sets allow completion of our circulation diagrams. In the eastern Alboran Sea, the old MAW, the WIW and the LIW, flowing from the north along the Spanish continental slope, more or less collide with the MAW that has recently entered through the Strait of Gibraltar. Therefore, all or a part of them is entrained off Algeria and, as a whole, they roughly flow cyclonically along the continental slope in most of the western Mediterranean Sea. The distribution of these water masses in the Algerian Basin is strongly dependent on the Algerian Current and on the various kinds of mesoscale anticyclonic eddies encountered there.