Modeling influence of CH4 ebullition on carbonate system in the East Siberian Arctic Shelf

Progressive permafrost thawing leads to excessive transport of organic matter (OM) from the land and massive bubbling methane (CH₄) release from degrading subsea permafrost in the Arctic shelf. The “extreme” aragonite under-saturation in the vast East Siberian Arctic Shelf (ESAS) reflects seawater acidity levels much higher than those projected in this region for the end of this century, as these are currently based only on atmospheric CO₂.(Semiletov et al., 2016). The changes in the carbonate system can be explained by an excessive production of carbon dioxide connected due to mineralization of land origin OM or /and oxidation of methane in the areas of intensive seeping.

Here, we analyze consequences of CH₄ oxidation on the carbonate system state in the methane seepage areas. We used biogeochemical model BROM coupled with a vertical 2 Dimensional Benthic-Pelagic Model 2DBP and bubble fate model (Yakushev et al., 2021). BROM is a detailed biogeochemical model for the water column, benthic boundary layer (BBL), and sediments. BROM considers interconnected transformations of species (N, P, Si, C, O, S, Mn, Fe) and resolves OM in nitrogen currency. BROM includes a module describing the carbonate equilibrium; this allows BROM to be used to calculate pH and carbonates saturation states, as well as processes of formation and dissolution of carbonates. The model's alkalinity variations take into account changes connected with redox reaction consuming or releasing proton. Methanogenesis and aerobic and anaerobic methane oxidation are also parameterized. The gas bubble fate module parameterizes bubbles rising and dissolution.  An application of the model allowed to estimate connection between an intensity of CH₄ release in the area (Shakhova et al., 2015) and changes in the carbonate system and to evaluate a volume of water affected. This research was funded by the Research Council of Norway: 315317 BEST-Siberian.

References:

Semiletov et al. (2016) Acidification of East Siberian Arctic Shelf waters through addition of freshwater and terrestrial carbon. Nat. Geosci., 9 (2016), pp. 361-365, 10.1038/NEGO2695

Shakhova N et al . ( 2015) The East Siberian Arctic Shelf: towards further assessment of permafrost-related methane fluxes and role of sea ice. Phil. Trans. R. Soc. A373: 20140451.http://dx.doi.org/10.1098/rsta.2014.0451

Yakushev E., Blomberg A.E.A., Eek E., Protsenko E., Totland C., Staalstrøm A., Waaru I.-K. Modeling of biogeochemical consequences of a CO2 leak in the water column with bottom anoxia. International Journal of Greenhouse Gas Control. 2021. 111: 103464.