The Black Sea is the largest meromictic marine basin characterized by well‐oxygenated surface waters and a deep sulfidic anoxic core, separated by a ca. 50‐m‐thick suboxic zone. Nitrogen cycling at oxic‐anoxic boundaries of oxygen‐depleted marine environments has been identified as a major source of nitrous oxide (N 2 O), a potent greenhouse gas. Contrary to this, previous work suggests that the Black Sea is considered only a...

Summary Coastal oceans receive large amounts of anthropogenic fixed nitrogen (N), most of which is denitrified in the sediment before reaching the open ocean. Sandy sediments, which are common in coastal regions, seem to play an important role in catalysing this N‐loss. Permeable sediments are characterized by advective porewater transport, which supplies high fluxes of organic matter into the sediment, but also leads to fluct...

Summary Methanotrophic bacteria represent an important biological filter regulating methane emissions into the atmosphere. Planktonic methanotrophic communities in freshwater lakes are typically dominated by aerobic gamma‐proteobacteria, with a contribution from alpha‐proteobacterial methanotrophs and the NC10 bacteria. The NC10 clade encompasses methanotrophs related to ‘ Candidatus Methylomirabilis oxyfera’, which oxidize me...