Methane excess in Arctic surface water-triggered by sea ice formation and melting

• Published in: Scientific Reports
• Main Authors: Damm, Ellen, Rudels, Bert, Schauer, Ursula, Mau, Susan, Dieckmann, Gerhard
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Nature 2015
• Subjects: Arctic; Arctic Ocean; Global warming; Sea ice
• Online Access: https://epic.awi.de/id/eprint/39023/; https://epic.awi.de/id/eprint/39023/1/srep16179.pdf; https://hdl.handle.net/10013/epic.46252; https://hdl.handle.net/10013/epic.46252.d001

Arctic amplificaton of global warming has led to increased summer sea ice retreat, which influencesgas exchange between the Arctic Ocean and the atmosphere where sea ice previously acted as a physical barrier. Indeed, recently observed enhanced atmospheric methane concentrations in Arctic regions with fractional sea-ice cover point to unexpected feedbacks in cycling of methane. We report on methane excess in sea ice-influencedwater masses in the interior Arctic Ocean and provide evidence that sea ice is a potential source. We show that methane release from sea ice into the ocean occurs via brine drainage during freezing and melting i.e. in winter and spring. In summer under a fractional sea ice cover, reduced turbulence restricts gas transfer, then seawater acts as bufferin which methane remains entrained. However, in autumn and winter surface convection initiates pronounced effluof methane from the ice covered ocean to the atmosphere. Our results demonstrate that sea ice-sourced methane cycles seasonally between sea ice, sea-ice-influencedseawater and the atmosphere, while the deeper ocean remains decoupled. Freshening due to summer sea ice retreat will enhance this decoupling, which restricts the capacity of the deeper Arctic Ocean to act as a sink for this greenhouse gas.