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Thermodynamic and kinetic control on anaerobic oxidation of methane in marine sediments |
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| Authors: | Nina J Knab Andrew W Dale Henrik Fossing |
| Institution: | a Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany b Utrecht University, Department of Earth Sciences, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands c National Environmental Research Institute, Department of Marine Ecology, Vejlsøvej 25, P.O. Box 314, 8600 Silkeborg, Denmark |
| Abstract: | The free energy yield of microbial respiration reactions in anaerobic marine sediments must be sufficient to be conserved as biologically usable energy in the form of ATP. Anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SRR) has a very low standard free energy yield of ΔG° = −33 kJ mol−1, but the in situ energy yield strongly depends on the concentrations of substrates and products in the pore water of the sediment. In this work ΔG for the AOM-SRR process was calculated from the pore water concentrations of methane, sulfate, sulfide, and dissolved inorganic carbon (DIC) in sediment cores from different sites of the European continental margin in order to determine the influence of thermodynamic regulation on the activity and distribution of microorganisms mediating AOM-SRR. In the zone of methane and sulfate coexistence, the methane-sulfate transition zone (SMTZ), the energy yield was rarely less than −20 kJ mol−1 and was mostly rather constant throughout this zone. The kinetic drive was highest at the lower part of the SMTZ, matching the occurrence of maximum AOM rates. The results show that the location of maximum AOM rates is determined by a combination of thermodynamic and kinetic drive, whereas the rate activity mainly depends on kinetic regulation. |
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