1 Department of Bioscience - Microbiology, Department of Bioscience, Science and Technology, Aarhus University2 Department of Bioscience - Center for Geomicrobiology, Department of Bioscience, Science and Technology, Aarhus University3 Department of Bioscience - Center for Geomicrobiology, Department of Bioscience, Science and Technology, Aarhus University4 Department of Bioscience - Microbiology, Department of Bioscience, Science and Technology, Aarhus University
Geochemical observations in marine sediment have recently documented that electric currents may intimately couple spatially separated biogeochemical processes (1). When marine sediment rich in iron sulphide was exposed to oxygen we observed how the electric currents resulted in significant geochemical alterations in the upper centimetres of the anoxic sediment: Sulphides were oxidized to sulphate in anoxic sediment layers. Electrons from this half-reaction were passed to the oxic layers cm above. In this way the domain of oxygen was extended far beyond it’s physically presence. Bioelectrical sulfide oxidation leads to electric field formation, sulfide depletion and acidification of the upper centimeters of the sediment. This promoted ion migration and dissolution of carbonates and iron sulfides. Sulfide released from iron sulfides was the major e-donor in the system. Ferrous iron released from iron sulfides was to a large extend deposited in the oxic zone as iron oxides and Ca2+ eventually precipitates at the surface as due to high pH caused by cathodic oxygen reduction. The result show how long distance electron transmission allows oxygen to drive the allocation of important minerals and possibly many trace elements deep in marine sediment.  Nielsen et al. (2010) Nature 463, 1071-1074.