Recent observations in marine sediment have revealed conductive networks transmitting electrons from oxidation processes in the anoxic zone to oxygen reduction in the oxiczone . The electrochemical processes and conductors seem to be biologically controlled and may account for more than half of the oxygen uptake in laboratory incubations of initially homogenized and stabilized sediment. Using microsensors and process rate measurements we further investigated the effect of the electric currents on sediment biogeochemistry. Dissolved sulfide readily donated electrons to the networks and could be depleted below detection limit in a several cm thick layer below the oxic zone. Subsequent dissolution of iron sulfide was indicated by mobilization of ferrous iron being precipitated again as ferric iron at the oxic-anoxic interface. Lowered sulfate reduction rates in the upper centimeters of the sediment confirmed the depth range of the electric communication and indicated donation of electrons directly from organotrophic bacteria. The separation of oxidation and reduction processes created steep pH gradients eventually causing carbonate precipitation at the surface. The results indicate that electron exchanging organisms have major biogeochemical importance as they allow widely separated electron donors and acceptors to react with one another.
Geochimica Et Cosmochimica Acta, 2010, Issue 12
Main Research Area:
Goldschmidt 2010; Earth, Energy, and the Environment