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

Puglini, Matteo; Brovkin, Victor; Regnier, Pierre; Arndt, Sandra

The East Siberian Arctic Shelf (ESAS) hosts large yet poorly quantified reservoirs of subsea permafrost and associated gas hydrates. It has been suggested that the global-warming induced thawing and dissociation of these reservoirs is currently releasing methane (inline-formulaCH4) to the shallow coastal ocean and ultimately the atmosphere. However, a major unknown in assessing the contribution of this inline-formulaCH4 flux to the global inline-formulaCH4 cycle and its climate feedbacks is the fate of inline-formulaCH4 as it migrates towards the sediment–water interface. In marine sediments, (an)aerobic oxidation reactions generally act as a very efficient methane sink. However, a number of environmental conditions can reduce the efficiency of this biofilter. Here, we used a reaction-transport model to assess the efficiency of the benthic methane filter and, thus, the potential for benthic methane escape across a wide range of environmental conditions that could be encountered on the East Siberian Arctic Shelf. Results show that, under steady-state conditions, anaerobic oxidation of methane (AOM) acts as an efficient biofilter. However, high inline-formulaCH4 escape is simulated for rapidly accumulating and/or active sediments and can be further enhanced by the presence of organic matter with intermediate reactivity and/or intense local transport processes, such as bioirrigation. In addition, in active settings, the sudden onset of inline-formulaCH4 flux triggered by, for instance, permafrost thaw or hydrate destabilization can also drive a high non-turbulent methane escape of up to 19 inline-formulaµmol inline-formulaCH4 cminline-formula−2 yrinline-formula−1 during a transient, multi-decadal period. This “window of opportunity” arises due to delayed response of the resident microbial community to suddenly changing inline-formulaCH4 fluxes. A first-order estimate of non-turbulent, benthic methane efflux from the Laptev Sea is derived as well. We find that, under present-day conditions, non-turbulent methane efflux from Laptev Sea sediments does not exceed 1 Gg inline-formulaCH4 yrinline-formula−1. As a consequence, we conclude that previously published estimates of ocean–atmosphere inline-formulaCH4 fluxes from the ESAS cannot be supported by non-turbulent, benthic methane escape.

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Puglini, Matteo / Brovkin, Victor / Regnier, Pierre / et al: Assessing the potential for non-turbulent methane escape from the East Siberian Arctic Shelf. 2020. Copernicus Publications.

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