Benthic nitrogen cycling in the deep ocean of the Kuroshio Extension region

Benthic nitrogen cycling, including nitrification, N-loss, and other transformations, plays a crucial role in the marine budget. However, studies on benthic cycling mainly focus marginal seas, while attention to deep ocean, which occupies largest area of seafloor, is severely lacking. In this study, we investigate Kuroshio Extension region (KE) northwest Pacific Ocean at water depths greater than 5,000 m through 15 N enrichment slurry incubation pore-water dissolved oxygen inorganic profiles. The indicates nitrification predominant process cycling. potential rates are nearly an order magnitude higher dissimilatory nitrate reduction. Nitrification total N-loss flux estimated from ammonium profiles 6–42 5–30 μmol −2 d −1 , respectively. Generally, anammox KE sediment. temperature gradient experiment that optimum for denitrification 13 41°C, respectively, partially explaining as dominant deep-ocean N-loss. Both low concentration discrepant results between anoxic amended with NO 3 − NH 4 + 14 suggest another limiting factor anammox. activity gradually declines distance Oyashio–Kuroshio transition zone. has opposite trend roughly. This reveals sediment transfers sink source north south. caused by variation primary production supplement active organic matter, energy microbes remineralization. Overall, our highlight two factors also exhibit tight coupling relationship pelagic cycle KE.