Vertical distribution of cadmium, copper and lead in the eastern Alboran Sea: enrichment of metals in surface waters

The vertical distribution of cadmium, copper and lead was studied in the 0–500 m layer of the Eastern Alboran Sea. The concentrations measured compare favourably with recent data for the neighbouring area (53 pM < Cd < 124 pM; 1.4 nM< Cu < 2.8 nM, and 90 pM < Pb < 310 pM). The analysis of six profiles showed the presence of a sub-surface water mass, the northwestern Mediterranean Water (NWMW, 75-30 m), with high concentration of trace metals. Metal-salinity relationships, typified by cadmium, showed that the Atlantic surface waters (ASW) with low metal concentrations before entering the Mediterranean Sea become enriched with metals from some as yet not clearly understood source near the Straits of Gibraltar. The salinity-Cd relationship, taken together with flux rates of salt and Cd, however, shows that the Modified Atlantic water (MAW) gains its high metal concentrations during its transit in the Alboran Sea principally from a mixing with the underlying metal-rich NWMW.