Marine circulation along the Ebro continental margin

Abstract Current meter and hydrographic data have been used to derive the marine circulation pattern along the Ebro continental margin. The main flow pattern is found along the slope, linked to the water mass structure at basin scale. Circulation stability under all seasonal conditions has been proved by 2 years of current meter data recorded at 8, 50 and 100 m at a shelf break station. The data indicate a permanent barotopic flow to the southwest; this is only altered by inertial oscillations and some short periods of current reversals, probably related to instabilities in the shelf/slope front present in the area. The data collected during a hydrographic cruise (October 1984) confirm that the topography plays a major role in defining the circulation pattern. Because of a sharp change in the wide eastward projection of the northern Ebro continental margin, the slope waters penetrate onto the shelf through a concavity of the bottom topography and cause a permanent local upwelling northeast of the delta. Diluted waters from the Ebro discharge are used as indicators of the shelf circulation. Two different waters of continental origin have been identified on the shelf, a colder water found on the surface near the river mouth that spreads to the south, and a warmer water probably formed in the southern bay of the Ebro Delta. The buoyancy input introduced by these fresher waters, together with topographic effects, produces small current gyres on both sides of the delta and reinforces the shelf/slope front that drives the general circulation to the south.