Particle fluxes and trace metal dispersal in the Gulf of Vera, SW Mediterranean Sea

Quantifying fluxes of particulate trace metals to the deep sea is a necessary step to understand their role in many oceanographic processes. The Gulf of Vera, in the SW Mediterranean Sea, is an ideal place to quantify these fluxes given the presence of a metal-rich mine tailings deposit in Portmán Bay, in its northern shore. Portmán Bay is one of the most extreme cases in Europe of mine waste impacts on coastal ecosystems, both inshore and offshore. About 57 million tons of tailings enriched in Fe, Pb, Mn, Zn, As, Ti and other metals were dumped there from 1957 to 1990 [1].

In the frame of the NUREIEV project, five mooring lines equipped with sediment traps and current meters were deployed in the wider Gulf of Vera. Three of the moorings were located in the middle course of three submarine canyons, one in the open continental slope and one in the deep basin. The monitoring period lasted for an annual cycle (March 2015 - March 2016). Our research focused on (1) measuring the temporal variability of particle fluxes in the study area, and (2) determining the concentration of particulate trace metals and metalloids (Zn, Pb, As, Ni, Cd, Cu, Co) as well as other metals (Fe, Mn, Ti) in settling particles.

Preliminary results within the following project NUREIEVA indicate that marine storms are the main processes triggering the transfer of particulate matter to the deep margin, mainly through hundred meters thick nepheloid layers moving not only along the submarine canyons but also across the open slope. High metal fluxes after storms reached up to 120.4 mg Pb m^-2d^-1, 282.3 mg Zn m^-2d^-1 and 40.4 mg As m^-2d^-1 in the canyon stations, four orders of magnitude higher than calculated in open Ligurian Sea [2]. This suggests that submarine canyons are efficient pathways for the transfer of pollutants from the shelf to the deep margin and basin [3].

Peak metal concentrations found so far in the wider Gulf of Vera exceed those found in other canyons in the Mediterranean Sea [2, 4]. The hypothesis that this could be related to the release of metals from the mine tailings deposit in Portmán is plausible but would require further work to be confirmed, including determination of enrichment factors in each station, and discerning between Portmán’s and other potential metal sources.

 

[1] Oyarzun, R. et al., 2013. Sci. Total Environ. 454-455, 245-249.

[2] Heimbürger, L.E. et al., 2012. Chem. Geol. 291, 141-151.

[3] Canals, M. et al., 2013. Prog. Oceanogr. 118, 1-27.

[4] Palanques, A. et al., 2008. Mar. Geol. 248, 213-227.