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Gulf of Cadiz - Environment

The pattern of the large scale circulation in the Gulf of Cadiz seems to be anticyclonic in summer, usually switching to cyclonic in winter. The anticyclonic circulation provides an oceanographic connection with the Alboran Sea in the Mediterranean Sea. During the upwelling season (April-September) an interesting thermal feature (the “Huelva front”) is formed in NW–SE direction in the northeast part of the Gulf of Cadiz. Under the influence of westerly winds, upwelled waters off Cape St. Vincent are advected to the east by the main current, reaching the vicinity of Cape St. Maria, where they join the waters upwelled there. Under the influence of easterly winds, a warm coastal countercurrent stretching east–west develops off the Guadalquivir River mouth. During summer when upwelling-favorable winds (westerlies) prevail for several days/weeks, waters keep moving eastwards, meeting the westward warm countercurrent and forcing the countercurrent to recirculate within the eastern shelf. A compensating current flows to the east along the outer shelf, and a cell of cyclonic circulation is established in the area (the Huelva Front). By contrast, when the easterlies prevail, upwelling off Cape St. Maria disappears, the decaying Huelva Front is forced to move westwards, and the warm coastal countercurrent flows over the western shelf.

The continental shelf expands progressively from a narrow strip (around 15 km) near the Portuguese border, to a large shelf (30-50 km) westward over Huelva and most of the Cadiz regions. Near the Gibraltar Strait the shelf tightens rapidly. The substratum in the wide continental shelf is mostly composed of sand/mud sediments, with some small rocky patches found in the province of Huelva. From Cape Trafalgar to the Gibraltar Strait, the soft bottom substrata and the gentle slope observed in most of the region changes suddenly to a rocky substratum, and a sharp slope .