The role of the Gulf of Cadiz circulation in the redistribution of trace metals between the Atlantic Ocean and the Mediterranean Sea.

The GoC shelf waters present much higher concentrations of dissolved Cu, Cd, and Zn than other coastal areas, constituting an important source of these elements onto its neighbouring basins, i.e., the Atlantic Ocean and the Mediterranean Sea. In this study we assessed the role of the GoC surface currents in the trace metals transport. For this purpose, ten dissolved (<0.22 µm) trace metals were sampled (Ag, Cd, Co, Cu, Fe, Mo, Ni, Pb, Zn, V) along the GoC continental shelf, and their spatial and temporal distribution was interpreted according to the surface circulation. Results show that the complex surface circulation over the shelf confines the metals concentration mainly along the inner shelf and determines their transport patterns: under southeastward currents, Cd, Co, Cu, Ni, and Pb are transported toward the Mediterranean Sea; under northwestward countercurrents, Cd, Co, Cu, Fe, Ni, and Zn are transported toward the southern and, occasionally, the western Portuguese shelf; under variable currents, Ag, Cd, Co, Cu, Fe, Pb, and Zn tend to accumulate near their source. Considering that some of these metals have not been analysed before in this region (Ag, Mo, V), or that the spatial distribution of certain metals (Ag, Fe, Mo, Pb, V) has not been interpreted in terms of the ocean circulation, this work could be considered as a baseline study for future comparisons.

Trace metal characterization and fluxes from the Guadiana, Tinto-Odiel and Guadalquivir estuaries to the Gulf of Cadiz.

Metals transported into the coastal zone by the South Iberian rivers are key to understand the biogeochemical cycles and distribution of trace elements in the Gulf of Cadiz (GoC hereinafter) and the exchange with the Mediterranean Sea. Previous studies carried out in the 80s have suggested that metal enrichment in the Alboran Sea (Western Mediterranean) is related with fluvial inputs from acid mine drainage from the Tinto and Odiel rivers. The present study evaluates the contribution of dissolved trace metal concentrations (i.e. Cd, Co, Cu, Fe, Mo, Ni, Pb, V, Zn) from the three main rivers discharging into the GoC (i.e. Guadiana, Tinto-Odiel and Guadalquivir rivers). Our results show that the metal composition of water discharged from each river is impacted by the activities developed in the course of the rivers, which clearly influence the GoC coastal surface waters composition. Metal fluxes from the Guadalquivir river are quantitatively higher than those from the Tinto-Odiel (e.g. up to 73% and 19% higher for Ni and Cu, respectively). Although the metal concentrations spatial distributions in the GoC are dominated by the circulation pattern between the Atlantic and the Mediterranean Sea, the concentrations within the GoC continental shelf could be explained by a greater contribution from the Guadalquivir estuary (e.g. 80.5%, 54.6%, 56.5% and 56.6% for Ni, Cu, Mo, and V respectively).