Hydrologie de la Mediterranee occidentale (secteur meridional et Golfe du Lion), en automne 1963 Campagne de la « Thalassa » du 12 octobre au 27 novembre

The western basin of the Mediterranean was the subject of follow-up hydrological observations during these last few years by ships of the Institute of Maritime Fishing. Knowledge of the thermohaline structure over the far-flung sectors of the coastal strip, that of the fronts that form upon contact with the various opposing masses of water, also that of the particularly active vertical movements in this sea were in fact necessary for attempting to locate the various marine species in their respective habitat. It is in this way that during the summer of 1957, the President Theodore Tissier undertook a campaign that encompasses the sectors of the Alboran Sea, the Catalan Sea, the Gulf of Lion and western Corsica. The results of these observations were published in 1960 by FURNESTIN as regards hydrology, by ALLAIN as regards dynamics. In autumn of the following year, the same ship worked in the entire zone included north of the 42nd parallel, from the Gulf of Lion to the Ligurian Sea (FURNESTIN and ALLAIN, 1962; ALLAIN, 1963). It was during the winter of 1960 that the President Theodore Tissier performed its last campaign, running along the edge of Algeria up to the 38th parallel (FURNESTIN and ALLAIN, 1962) and, when the Thalassa took over in 1961, two additional sections were carried out, also in winter, between Ivice and western Sardinia, at the 40th parallel and from there to Algiers (FURNESTIN and ALLAIN, 1962). In the meanwhile, the President Theodore Tissier was able to conduct a special study of the Strait of Gibraltar, focusing on the variations of the hydrological and dynamic regimes during the summer of 1959 (ALLAIN, 1964). As a follow-up to these campaigns that, carried out in different seasons, already showed the variations that can occur in the hydrological pattern during the year, it was appropriate to study once again, during a transitional period, this zone, which is the southern sector of the western basin, that is directly influenced by the Atlantic current. So it is autumn 1963 that we have chosen to redo normal sections to the Algerian coast and continued up to meridians 38°30 to 39°. An oblique profile, ranging from western Sardinia to the Gulf of Lion allowed us, moreover, to compare our data with those of autumn 1958 in the north of the basin. A special study of the Gulf of Lion was at last undertaken in order to examine the variations that occurred with respect to the results of the two preceding campaigns carried out on this plateau. We will not review the previous research that was cited in preceding publications and to which we will refer during our description of this study.