Methane distribution, production, and emission in the Western North Pacific

Ocean is a net source of atmospheric methane (CH₄), but there are still large uncertainties in the estimations of global oceanic CH₄ emission due to sparse data coverage. In this study, we investigated the spatial distribution and influencing factors of CH₄ in the Western North Pacific (WNP) during two cruises in 2021 and 2022. High-resolution continuous underway measurements showed that surface CH₄ concentrations ranged from 1.95 to 3.92 nM, indicating an obvious spatial gradient with a gradual increase from the south to the north due to the influence of water mixing and primary productivity. Vertically, subsurface CH₄ maxima were ubiquitously observed due to in situ production through multiple pathways including MPn degradation and phytoplankton production. Surface water was oversaturated with respect to the atmospheric CH₄ with the air-sea CH₄fluxes in the tropical Western Pacific (1.28 ± 1.12 μmol/m²/d) higher than those in the Kuroshio Extension region (2021: 0.49 ± 0.89 μmol/m²/d; 2022: 0.37 ± 0.53 μmol/m²/d). Overall CH₄ emission from the Western North Pacific is 0.08 Tg/yr, accounting for 13% of the total emission from the open ocean.