High methane emissions from an anoxic fjord driven by mixing and oxygenation

[摘要] Oceanic methane (CH 4 ) budgets lack data from high-latitude fjords that often behave as intermittently anoxic ecosystems with potentially high methane emissions. We conducted 15 expeditions and 49 in situ lander deployments in an anoxic Scandinavian fjord between 2009 and 2021. Benthic fluxes were highest at the deepest anoxic site (average 516  μ mol CH 4 m −2 d −1 ), supporting bottom water methane exceeding 5000 nM. Natural and engineered mixing events displaced methane-rich bottom waters, enhancing upper water concentrations and driving high sea–air flux reaching 641  μ mol CH 4 m −2 d −1 . Mixing also reduced pelagic methane oxidation from 70% to 20% of all methane sources into the fjord. Upscaling of literature fluxes combined with our results suggests that fjords globally emit 1.0 ± 0.8 Tg CH 4 yr −1 . Despite their small global area, fjords are hotspots of methane release. We suggest that ongoing deoxygenation and global change will enhance methane emissions from fjords.

[学科分类] 口腔科学