Exploring the efficiency of anaerobic oxidation of methane as a sink to hydrate-sourced methane

Ocean warming threatens methane hydrate stability in continental margins, potentially leading to methane release into marine sediments, the water column, and ultimately the atmosphere. Over the decadal to millennial timescales during which hydrate-sourced methane release is anticipated, microbially mediated anaerobic oxidation of methane (AOM) in marine sediments may mitigate benthic methane efflux. While traditionally considered a highly efficient biofilter, recent studies reveal significant variability in the AOM sink efficiency. For instance, in cold seep settings, efficiency ranges from 80% to 20% with slow to high fluid flow, respectively, and this decreases to around 10% in pristine seepage environments. This variability is directly related to the balance between multiphase methane transport and the growth dynamics of microbial communities.

In this study, we use a novel 1D multiphase reaction-transport model to investigate the transient evolution of the AOM sink efficiency and its impact on seafloor methane emissions in response to a centennial-scale methane release caused by climate-driven hydrate destabilization. We examine the combined influence of gaseous methane transport, including induced tensile fracturing by pore fluid overpressure, and methanotrophic biomass dynamics on weakening the efficiency of the AOM sink. Preliminary findings suggest that the AOM sink is notably limited to mitigating benthic methane emissions in gassy sediments. Additionally, the slow growth rate of methane-oxidizing microorganisms may lead to significant temporal windows for methane to escape into the ocean. This integrated analysis provides insights into the intricate dynamics governing the efficiency of the benthic AOM sink subjected to hydrate-sourced methane. It contributes to a more comprehensive assessment of potential methane emissions in continental margins in the context of global warming.