Distribution and behaviour of some dissolved trace metals in the western Mediterranean Sea

Concentrations of a number of trace metals have been measured in samples obtained on a series of cruises in the western basin of the Mediterranean, carried out as part of the EROS 2000 project. The Mediterranean distributions of Cd, Cu and Ni, metals which show varying degrees of nutrient-like behaviour in the world ocean, are dominated by lateral transport and vertical mixing processes, rather than biogeochemical cycling. In particular, Cu shows a clear distinction between depleted upper waters with a high proportion of Atlantic Surface Water, and waters of similar salinity but subject to terrestrial influences. The behaviour of Cd is more complex, as a result of both non-conservative estuarine mixing and inputs of Cd-enriched North Atlantic Central Water entrained with the surface inflow through the Gibraltar Straits. This entrainment of relatively small volumes of high-Cd water has a potentially important effect on Mediterranean budgets of this metal. Dissolved Mn, Co and Pb distributions are closer to those found elsewhere in the world ocean. Atmospheric inputs are clearly distinguishable for Mn and Ph, although riverine inputs are dominant in the coastal zone. All the metals discussed show some degree of enrichment around the Straits of Gibraltar and Sicily, apparently a result of a combination of localized influences from highly mineralized adjacent regions.