Can anaerobic oxidation of methane prevent seafloor gas escape in a warming climate?

Christian Stranne1,2, Matt O'Regan1,2, Martin Jakobsson1,2, Volker Brüchert1,2, and Marcelo Ketzer3

1 Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden
2Bolin Centre for Climate Research, Stockholm University, 106 91 Stockholm, Sweden
3Department of biology and environmental science, Linnaeus University, 391 82 Kalmar, Sweden

Abstract
Assessments of future climate-warming-induced seafloor methane (CH4) release rarely include anaerobic oxidation of methane (AOM) within the sediments. Considering that more than 90 % of the CH4 produced in ocean sediments today is consumed by AOM, this may result in substantial overestimations of future seafloor CH4 release. Here, we integrate a fully coupled AOM module with a numerical hydrate model to investigate under what conditions rapid release of CH4 can bypass AOM and result in significant fluxes to the ocean and atmosphere. We run a number of different model simulations for different permeabilities and maximum AOM rates. In all simulations, a future climate warming scenario is simulated by imposing a linear seafloor temperature increase of 3 ∘C over the first 100 years. The results presented in this study should be seen as a first step towards understanding AOM dynamics in relation to climate change and hydrate dissociation. Although the model is somewhat poorly constrained, our results indicate that vertical CH4 migration through hydraulic fractures can result in low AOM efficiencies. Fracture flow is the predicted mode of methane transport under warming-induced dissociation of hydrates on upper continental slopes. Therefore, in a future climate warming scenario, AOM might not significantly reduce methane release from marine sediments.

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