Assessing the potential for non-turbulent methane escape from East Siberian Arctic Shelf

• Published in: Biogeosciences
• Main Authors: Puglini , M., Brovkin, V., Reginer, P., Arndt, S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: Arctic; Global warming; permafrost
• Online Access: http://hdl.handle.net/21.11116/0000-0003-FC9E-0; http://hdl.handle.net/21.11116/0000-0003-FCA0-C; http://hdl.handle.net/21.11116/0000-0006-7297-F; http://hdl.handle.net/21.11116/0000-0006-729B-B; http://hdl.handle.net/21.11116/0000-0006-B8A6-F

East Siberian Arctic Shelf (ESAS) hosts large, yet poorly quantified reservoirs of subsea permafrost and associated gas hydrates. It has been suggested the global-warming induced thawing and dissociation of these reservoirs is currently releasing methane to the shallow shelf ocean and ultimately the atmosphere. However, the exact contribution of permafrost thaw and methane gas hydrate destabilization to benthic methane efflux from the warming shelf and ultimately methane-climate feedbacks remains controversial. A major unknown is the fate of permafrost and/or gas hydrate-derived methane as it migrates towards the sediment-water interface. In marine sediments, (an)aerobic oxidation reactions generally act as extremely efficient biofilters that often consume close to 100 % of the upward migrating methane. However, it has been shown that a number of environmental conditions can reduce the efficiency of this biofilter, thus allowing methane to escape to the overlying ocean. Here, we used a reaction-transport model to assess the efficiency of the benthic methane filter and, thus, the potential for permafrost and/or gas hydrate derived methane to escape shelf sediments under a wide range of environmental conditions encountered on East Siberian Arctic Shelf. Results of an extensive sensitivity analysis show that, under steady state conditions, anaerobic oxidation of methane (AOM) acts as an efficient biofilter that prevents the escape of dissolved methane from shelf sediments for a wide range of environmental conditions. Yet, high CH4 escape comparable to fluxes reported from mud-volcanoes is simulated for rapidly accumulating (sedimentation rate > 0.7 cm yr−1) and/or active (active fluid flow > 6 cm yr−1) sediments and can be further enhanced by mid-range organic matter reactivity and/or intense local transport processes, such as bioirrigation. In active settings, high non-turbulent methane escape of up to 19 μmolCH4 cm−2 yr−1 can also occur during a transient, multi-decadal period following the sudden onset of ...