Seasonal variation of fluxes and distributions of dissolved methane in the North Yellow Sea

The concentrations and sea-to-air fluxes of dissolved methane (CH4) were investigated in the North Yellow Sea during August 2006, January, April and October 2007. Dissolved CH4 concentrations showed obvious seasonal variation, with maximum values occurring in summer and lowest values occurring in winter. The saturations of dissolved CH4 in surface waters ranged from 78.7% to 1679.7% with an average of 252.4%. The estimated atmospheric CH4 fluxes using the Liss and Merlivat (LM86), and Wanninkhof formulae (W92) were (4.2±4.7), (11.6±10.3), (8.5±12.7) and (0.2±1.0), and (6.9±7.3), (14.6±22.3), (13.8±14.3) and (0.4±1.7) μmol·(m2 d)−1, respectively, for spring, summer, autumn and winter. Based on the average annual atmospheric CH4 flux and the area of the North Yellow Sea, the annual CH4 emission was estimated to be (2.4×10−2–4.2×10−2) Tg a−1, which suggests that the North Yellow Sea was a net source of atmospheric CH4.