杭州湾沉积物中甲烷的垂向分布及控制因素

近海特别是河口三角洲地区的沉积物中蕴藏着大量的甲烷。作为一种温室气体和海洋地质灾害因素，研究近岸海底沉积层中甲烷气体的赋存特征，可为海底浅层气的灾害防控、生态环境效应研究等提供理论支撑。通过对杭州湾YS3、YS4、YS6和YS7四个沉积物钻孔（长约60 m）的地质与地球化学参数的分析，探讨了研究区沉积层中CH4气体的垂向分布特征及影响因素。结果表明：YS3和YS6孔均存在一个含甲烷气层，分别位于海底1.5～22.5和8～42 mbsf，而YS4和YS7孔均存在两个含甲烷气层，分别位于约5 ～ 11和23～47 mbsf。四个钻孔中甲烷主体埋藏于粉砂和黏土为主的沉积层中，CH4最高含量分别为5.66、1.73、1.96和2.12 mM，均为CO2/H2还原途径生成，生成后在海底原位沉积层中甲烷的扩散迁移和厌氧氧化作用达到了动态平衡。沉积物孔隙度、黏土含量、有机碳含量、沉积速率等是海底甲烷的含量、分布层数、分布深度和赋存厚度的重要影响因素。

Vertical distribution and controlling factors of methane in sediments of Hangzhou Bay

A large amount of methane is trapped in the sediments of estuarine delta. As a factor of greenhouse gas and a marine geological hazard, the occurrence features of methane in marine sediments can provide theoretical support for shallow gas prevention measures and eco-environmental effects. Based on the test results and geochemical parameters of cores YS3, YS4, YS6, and YS7 in Hangzhou Bay, the methane vertical distribution and the controlling factors were studied. We found one layer of methane gas in 1.5～22.5 mbsf in YS3 and 8～42 mbsf in YS6, and two layers of methane gas in 5～11 mbsf in YS4 and 23～47 mbsf in YS7. Methane in each core was buried in silt and clay-dominated sedimentary layers; the highest contents of CH4 in the YS3, YS4, YS6, and YS7 cores were 5.66 mM, 1.73 mM, 1.96 mM, and 2.12 mM, respectively, and generated through CO2/H2 reduction pathway. The diffusion migration and anaerobic oxidation of methane reached a dynamic equilibrium in the in-situ marine sediment layer. Sediment porosity, clay content, and organic carbon content were important influencing factors on the contents, distribution layers, buried depth, and thickness of methane in the Hangzhou Bay marine sediments.