1. 国家海洋局海底科学重点实验室，国家海洋局第二海洋研究所，浙江 杭州 310012
• 收稿日期:2003-10-16 修回日期:2004-03-02 出版日期:2004-12-20
• 通讯作者: 于晓果（1964-），女，山东潍坊人，研究员，主要从事海洋有机地球化学与古环境及油气地球化学研究. E-mail:E-mail：yuxgsio@mail.hz.zj.cn
• 基金资助:

国家重点基础研究发展规划项目“中国边缘海的形成演化及重要资源的关键问题”（编号：G200006700）资助

### ADVANCES IN GAS HYDRATE DISSOCIATION AND EFFECTS ON THE ECOLOGY AND ENVIRONMENT

YU Xiao-guo, LI Jia-biao

1. Key Labortory of Submarine Geosciences, Second Institute of Oceanography, SOA, Hangzhou 310012,China
• Received:2003-10-16 Revised:2004-03-02 Online:2004-12-20 Published:2004-12-01

Understanding the formation/dissociation of the gas hydrate and the effects on sediments, water column and chemosynthetic communities could shed light on several broader issues, like climate-forcing by gas hydrate eruption on global and regional scales; the role of methane hydrate in the carbon cycle; and the mechanism about flux fluid and exchange. Here in this review paper the authors introduce and outline some advances in gas hydrate and global warming; anaerobic methane oxidation; authigenic carbonate and chemosynthetic communities. 
Methane is radiatively active. It is a greenhouse gas that has a global warming potential 20 times greater than an equivalent weight of carbon dioxide. The amount of methane that is present in gas hydrate onshore and offshore is perhaps 3,000 times the amount in the present atmosphere; an instantaneous release of methane from this source could have an impact on atmospheric composition and thus on the  radiative properties of the atmosphere that affect global climate. Polar ice cores document large oscillations inatmospheric methane (CH4) associated with Quaternary climate cycles on orbital, millennial, and decadal time scales. Dramatic warming during the first few decades of interglacials and interstadials coincided with rapid atmospheric CH4 increase. These rises in CH4have been attributed to, in one hypothesis, enhanced methanogenesis in tropical wetlands receiving greater precipitation . Another potential source of atmospheric CH4 is gas hydrate. 
Anaerobic methane oxidation is a process that effectively controls emission of methane from many anaerobic environments into the atmosphere and thus plays an important role in the global methane budget. Two scenarios for anaerobic methane oxidation have been proposed: (i) a single sulfate-reducing bacterium and (ii) a consortium of different bacteria. The consortium hypothesis assumes that methane is oxidized by an unknown bacterium in association with a sulfate reducer. 
Carbonate precipitation is a striking phenomenon that occurs at cold seeps. It has been assigned to coupled bacterial sulphate reduction and methane oxidation. This reaction is associated with an increase in alkalinity which favours carbonate precipitation. The typical carbonate species at cold seeps are Mg-calcite, aragonite, and dolomite. The typicalδ13C from carbonates formed at methane〖KG1〗vent show light values between -70‰ and -20‰ PDB; δ18O are heavier , between 3‰ to 7‰ PDB. Apart from carbonates, barite has also been observed at cold seeps. It is understood now that barite forms by the interaction of Ba-rich and sulfate-free ascending fluids with dissolved sulfate of pore water in higher strata or the bottom water.
The LPTM is that 55 Ma was characterized by a 4 to 6℃ rise in deep ocean water temperature and extraordinary injection of 12C-rich carbon into the exogenic carbon cycle. The best explanation for the carbon cycle perturbation is that the bottom water warming converted massive amounts of marine hydrate to free CH4gas, and this CH4 added to ocean. The 5℃ warming of bottom waters increased temperatures in space art depth, converting about 5000 Gt of gas hydrate to free gas, and 1900 Gt of free gas were directly injected into the water column with sediment failure between 900~200m below the sea level.
Chemosynthetic communities were later found to be able to extract their energetic needs from dissolved gasses in their environment in the presence of dissolved oxygen. The most conspicuous fauna of cold seepecosystems are large vesicomyid clams, mytilid mussels, vestimentiferan tubeworms and cladorhizid and hymedesmiid sponges. All chemosynthetic species studied to date have a very slow growth rate. Communities can change rapidly over distances of only a few meters.
The dissociation of gas hydrate and the effects on marine, even on the earth, deeply reflect the interrelations and interactions on each sphere. Biomass, especially microbiomass especiaaly are very important in methane budget and authigenic minerals precipitation. 