Methane production, consumption and its carbon isotope ratios in the Southern Ocean during the austral summer

Abstract

Abstract. The distribution of dissolved CH4 in the Southern Ocean at 140° E was measured during the austral summer. Surface CH4 was supersaturated on average, and the calculated mean sea-air flux rate was 0.32 μmol m−2 d−1. The vertical distributions exhibited a CH4 maximum at approximately 125 m (ΔCH4, 2.94 nM) below the chlorophyll-rich layer, suggesting a relationship between CH4 production and plankton dynamics in this area. CH4 oxidation and ocean movement characteristics in the deep layer led to the enrichment and fluctuation of δ13CCH4. We estimated the influence of Southern Ocean CH4, a source of isotopically heavy CH4 to the atmosphere, on the global CH4 budget to be approximately 0.19 Gg d−1.