Methane Distribution, Production, and Emission in the Western North Pacific

The ocean is a source of atmospheric methane (CH 4 ), but there are still large uncertainties in the estimations of global oceanic CH 4 emission due to sparse data coverage. In this study, we investigated the spatial distribution and influencing factors of CH 4 in the Western North Pacific (WNP) during May–June 2021. High‐resolution continuous underway measurements showed that surface CH 4 concentrations indicated an obvious spatial gradient with an increase from the south to the north due to the influence of water mixing between Kuroshio Extension (KE) and Oyashio. Surface water was generally oversaturated with respect to the atmospheric CH 4 , and high CH 4 fluxes occurred in the Kuroshio‐Oyashio transition region due to high productivity and intensive air‐sea interaction, emphasizing the importance of the Kuroshio‐Oyashio transition region in global oceanic CH 4 emission. Vertically, subsurface CH 4 maximums were observed around 50–300 m due to in situ production through multiple pathways, and their distributions in the water column were affected by subduction of North Pacific Intermediate Water (NPIW) and advective transport. Methylphosphonate (MPn) enrichment experiment and 16S rRNA gene sequencing showed that in subtropical region and Kuroshio‐Oyashio transition region, Vibrio spp. might produce CH 4 by degrading MPn. Although this process was inhibited by inorganic phosphorus and regulated by iron stress, it might be a potential source of CH 4 in the oxygenated water in the WNP. Our results contribute to better constrain the global oceanic CH 4 emission, and help understanding the role of biological and physical processes in regulating CH 4 emission in the WNP.