Oceanic methane (CH₄) 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 μmol CH₄ 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 μmol CH₄ 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 CH₄ 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.

中文翻译：

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由混合和氧化驱动的缺氧峡湾的高甲烷排放

海洋甲烷 (CH ₄ ) 预算缺乏来自高纬度峡湾的数据，这些峡湾通常表现为具有潜在高甲烷排放量的间歇性缺氧生态系统。2009 年至 2021 年间，我们在缺氧的斯堪的纳维亚峡湾进行了 15 次探险和 49 次原地着陆器部署。在最深的缺氧地点（平均 516  μ mol CH ₄ m ^-2 d ^-1），底栖通量最高，支持底水甲烷超过 5000纳米。自然和工程混合事件取代了富含甲烷的底层水，提高了上层水的浓度并推动海气通量达到 641  μ mol CH ₄ m ^-2 d ^-1. 混合还减少了进入峡湾的所有甲烷来源的 70% 到 20% 的远洋甲烷氧化。文献通量的升级与我们的结果相结合表明，全球峡湾排放 1.0 ± 0.8 Tg CH ₄ yr ^-1。尽管全球面积很小，但峡湾是甲烷释放的热点。我们建议，持续的脱氧和全球变化将增加峡湾的甲烷排放。