Recent studies in aquatic environments have indicated that microbial methane production is not limited to strictly anoxic conditions and is widespread in the oxic water column. Based on recent investigations proposing linkage between the microbial turnover of methylphosphonate (MPn) and the widespread methane oversaturation in surface waters, we conducted an MPn/^(13)C-MPn tracer approach that combines liquid chromatography-mass spectrometry and gas chromatography-stable isotope ratio …