Impact of electrogenic sulfur oxidation on trace metal cycling in a coastal sediment

Electrogenic sulfur oxidation (e-SOx) is a newly discovered pathway of microbial sulfide oxidation, mediated by so-called cable bacteria. The reduction of oxygen near the sediment-water interface is coupled by long-distance electron transport to the oxidation of sulfide in deeper sediment, and in this way, electrical currents are induced within the seafloor that range over centimeter scale distances. Previously, electrogenic sulfur oxidation has been shown to generate extreme pH excursions in the pore water, and as a result, the process strongly amplifies the cycling of various pH-sensitive minerals, such sulfide minerals and carbonates. Here we show that e-SOx also strongly influence the early diagenesis of trace metals in coastal sediments. For this, field observations at a shallow subtidal site in the North Sea were combined with dedicated laboratory incubations of repacked sediments. High resolution microsensor profiling (pH, H₂S and O₂) confirmed the typical geochemical signature of e-SOx both in situ as in the laboratory experiments. Pore water analysis revealed a strong mobilization of both arsenic and cobalt within the electro-active sediment zone. The dissolution of iron sulfides, resulting from the acidification of the pore water by e-SOx, appears to be the main driver for the observed release of cobalt and arsenic. The current generated by e-SOx affects charged species. In this manuscript, we have proposed a new estimation method for the associated current density, based on the rate of sulfide oxidation.Overall, electrogenic sulfur oxidation has a major impact on the cycling of arsenic and cobalt in coastal sediments, and may substantially increase the effluxes of these trace metals to the coastal ocean