Distribution of dissolved methane concentration and its flux in early autumn in the Yangtze Estuary-Hangzhou Bay

Based on the field survey in the Hangzhou Bay-Yangtze Estuary in September 2022, dissolved methane concentration and its sea-to-air flux and related dominant factors were studied. Results showed that dissolved methane concentration ranged from 6.89 to 43.41 nmol/L with an average of (18.58 ±8.88) nmol/L in surface seawater, and from 8.88 to 36.15 nmol/L with an average of (8.25 ± 89.34) nmol/L in bottom seawater, respectively. Dissolved methane concentration was higher in the Yangtze Estuary and Hangzhou Bay than in the offshore area, indicating that freshwater input from local sediment played an important role in methane sources. The average saturation of dissolved methane in surface seawater and its sea-to-air flux was (275.10 ± 6.70)% and (157.40 ± 145.68) μmol/(m2·d), respectively, suggesting the survey area was a net source of atmospheric methane. Annual methane of emission was estimated to be approximately 1.78×109 mol, accounting for about 0.16% of the global annual oceanic methane emission, which caused an average elevation of 3.2 nmol/mol methane in the boundary air of survey area.

本数据集基于2022年9月在杭州湾-长江口开展的野外调查，对海水溶解甲烷浓度、海-气通量及其相关主控因素进行了研究。结果表明：表层海水溶解甲烷浓度范围为6.89~43.41 nmol/L，平均值为(18.58±8.88) nmol/L；底层海水溶解甲烷浓度范围为8.88~36.15 nmol/L，平均值为(8.25±89.34) nmol/L。长江口与杭州湾海域的溶解甲烷浓度高于近海区域，表明当地沉积物输入的淡水是甲烷的重要来源。表层海水溶解甲烷平均饱和度及海-气通量分别为(275.10±6.70)%和(157.40±145.68) μmol/(m²·d)，显示本次调查海域为大气甲烷的净源。经估算，该海域年甲烷排放量约为1.78×10⁹ mol，约占全球海洋甲烷年排放量的0.16%，可使调查区域边界大气中的甲烷浓度平均升高3.2 nmol/mol。