The iron "redox battery" in sandy sediments: Its impact on organic matter remineralization and phosphorus cycling.

Permeable sandy sediments cover 50-60 % of the global continental shelf and are important bioreactors that regulate organic matter (OM) turnover and nutrient cycling in the coastal ocean. In sands, the dynamic porewater advection can cause rapid mass transfer and variable redox conditions, thus affecting OM remineralization pathways, as well as the recycling of iron and phosphorus. In this study, North Sea sands were incubated in flow-through reactors (FTRs) to investigate biogeochemical processes under porewater advection and changing redox conditions. We found that the average rate of anaerobic OM remineralization was 12 times lower than the aerobic pathway, and Fe(III) oxyhydroxides were found to be the major electron acceptors during 34 days of anoxic incubation. Reduced Fe accumulated in the solid phase (expressed as Fe(II)) before significant release of Fe

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Declaration of competing interest The Authors declare that there is no conflict of interest.