ANAEROBIC OXIDATION OF METHANE AND SEEP CARBONATE PRECIPITATION KINETICS AT SEAFLOOR

Anaerobic methane oxidation(AMO)is a globally important biogeochemistry process,which has been identified by sufficient geochemical evidence.Unfortunately,the mechanism of AMO is controversial and may be a reverse-methanogenesis process.So the fundamental understanding of the AMO in the global carbon cycle is still lacking.At many gas vent sites authigenic carbonate precipitates because of release of carbonate alkalinity from the AMO.Carbonate precipitation often induces accumulation of carbonate crust at the sediments surface or within shallow surface sediments.Physical and biogeochemical conditions allowing carbonate crust formation are largely unknown.Carbonate crusts are built under a narrow range of physical,chemical and biological conditions.The simulations show that carbonate crusts in the sediments only form when the fluids contain sufficient dissolved methane,with moderate upward fluid flow velocity and when bioturbation coefficents are low.Moreover,high sedimentation rate inhibit crust formation.Thus,seep carbonates at seafloor are indicators of the evolvement of gas venting system.Based on the recent results of AMO and seep carbonate formation,the authors reviewed mechanism of AMO,relevance to ecology and environmental effect,rate of AMO,kinetics of crust formation and its controls.