Hydrologie variations saisonnieres de la situation thermique du Golfe de Gascogne en 1967

Knowledge of the hydrological regime of an oceanic sector such as the Gulf of Gascony is of vital interest for an ecological study of fish and other marine species. We have of course many data on this region where the Institute of Maritime Fishing has been conducting its research for 50 years now. But what was missing was a systematic seasonal study of the entire Gulf covering several years. A study of this kind, limited to the continental shelf but linked to more extensive research that will be published at a later time, was undertaken in 1967. The subject of this paper is its first results. The method used consisted in plotting a network of 134 stations in the sector delineated by the French coast, the mouth of the English Channel, a line linking the Isles of Scilly to Petite Sole and the depth contour of 200 metres (figure 1) and in creating these stations using the bathythermograph. In fact, temperature was the factor that, biologically speaking, interested us the most and this method gave us, moreover, the means of obtaining the maximum amount of information in a relatively limited amount of time, allowing us to set up the most representative thermal maps of the situation of the moment. Thus the four campaigns, conducted with the Institute of Fishing's ship La Pélagia, take place in winter, from 13 February to 22 March, in summer between 21 July and 10 August, in the spring, from 16 May to 7 June, and in the fall, from 7 to 24 November. The following operations were performed at each of these campaigns: a) on each station, a continuous report of the temperature from the surface up to the area near the bottom, using a Richard bathythermograph (± 0°1 precision, depth error not exceeding 1%) and a simultaneous verification of the surface temperature done by means of a Yoshino reversing thermometer precise to 1/100th of a degree; b) once per day on a deep station, monitoring of the bathythermograph's readings while observing the temperature at standard levels using a series of Yoshiono thermometers.