Biogeochemical Signatures on Methane Oxidations in The Seafloor of The Arctic

Abstract

Large quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we focused on biogeochemical processes that regulate methane fluxes across the seafloor of the Arctic (Beafort Sea and Chukchi Sea). We found that methane ascending from the subsurface was significantly regulated by anaerobic and aerobic oxidation of methane (AOM and MOx) in the sediment depths where there were suitable conditions related to the supply of electron acceptors (sulfate and oxygen). In this regard, AOM- and MOx-related microbial communities (ANME-1, -2 and -3, and Methylococcales) showed the preferential niche between both seeping structures (mud volcanoes and gas hydrate bearing mounds). The discriminative distributions of these communities seem to be due to various environmental factors such as the type of locally geological setting and advective/diffusive methane fluxes. It infers that the niche diversification of the seep-inhabiting microbial communities may be shaped by local conditions rather than geographic distances. Particularly, with respect to dramatic Arctic warming in present, a greater proportion of methane is transported by advection or in the gas phase, which may reduce the efciency of the methanotrophic sink. Thus, our findings reveal that further observations such as quantitative methane turnover, the effect of dissociated reservoirs, and bubble transports are required to fully understand the methane oxidations which play an important process as negative feedback pathways for the Arctic warming.