Submarine groundwater discharge: A significant source of dissolved trace metals to the North Western Mediterranean Sea

Bioactive trace metals play a significant role as micronutrients in the ocean and therefore it is important to evaluate their sources. Submarine groundwater discharge (SGD) has been recognized as an input of trace metals to the coastal sea. Here, we investigated the significance of SGD as a source of dissolved trace metals (dTM) to the coastal sea in a regional area such as the North Western (NW) Mediterranean Sea. We analysed dTM concentrations in SGD end-members and incorporate data on SGD dTM concentrations and water flows reported in previous studies carried out in this area, to estimate the following ranges of SGD-driven dTM fluxes (in 10 mol y): Cd: 0.0007–0.03, Co: 0.004–0.11, Cu: 0.09–1.9, Fe: 1.8–29, Ni: 0.09–1.9, Pb: 0.002–0.06, Zn: 0.38–12. These fluxes were compared to dTM fluxes from riverine discharge and atmospheric deposition, demonstrating that SGD is a major source of dTM to the NW Mediterranean Sea. Whilst riverine inputs are limited to the surrounding of river mouths and atmospheric fluxes are distributed throughout the whole basin mainly during sporadic depositional events, SGD represents a permanent, albeit seasonally variable, source of metals to most of the coastal areas. SGD-driven dTM inputs may be even more significant, in relative terms, in other coastal regions of the Mediterranean Sea where rivers are scarce, as it is the case of the African coast and many islands. This study highlights the relevance of SGD as a source of dTM to the Mediterranean Sea and the need of its consideration in the calculation of metal budgets in the basin and in the investigation of biogeochemical cycles in coastal areas.This project has been partially funded by the European Union Seventh Framework Programme through the MetTrans Initial Training Network, Marie Curie Actions, which also provide financial support through a PhD fellowship to G.T. (EU FP7-People-2011-ITN-290336). Support provided by the Generalitat de Catalunya to MERS (2014 SGR – 1356) is also acknowledged. V.R. acknowledges financial support from the European Union's FP7 (Marie Curie Actions PCOFUND-GA-2013-609102), through the PRESTIGE programme coordinated by Campus France. The Spanish Government (MINECO) is acknowledged for support to E.G-S through a post-doctoral grant (FPDI-2013-15660) and support of ECOALFACS project (CTM2009-09581) to the ICM-CSIC. This research is also a contribution to the ANR @RAction chair (ANR-14-ACHN-0007-01) and Labex OT-Med (ANR-11-LABEX-0061) funded by the “Investissements d'Avenir” program through the A*MIDEX project (ANR-11-IDEX-0001-02) of the French National Research Agency (ANR).Peer Reviewe