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| 天然气水合物分解及其生态环境效应研究进展 | |
| 引用本文： | 于晓果,李家彪.天然气水合物分解及其生态环境效应研究进展[J].地球科学进展,2004,19(6):947-954. |
| 作者姓名： | 于晓果 李家彪 |
| 作者单位： | 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 |
| 基金项目： | 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 |
| 摘 要： | 了解大陆／大洋边缘地区天然气水合物形成与分解及其在海底沉积物、水体及海底化学自氧生物群落中的一系列物理、化学及生物作用有助于我们在全球和区域尺度上探讨天然气水合物分解对气候变化的影响;天然气水合物在碳循环中的作用和大陆边缘流体活动与物质交换机制等问题。从水合物分解与全球变暖、贫／缺氧甲烷氧化作用、自生矿物沉淀、化学自养生物群落等方面综述了水合物的环境生态效应研究进展。天然气水合物的形成／分解及
其对海洋乃至全球环境生态变化的影响,深刻地反映了地球上岩石圈、水圈、大气圈和生物圈之间相互联系与相互作用,生物,特别是微生物对全球CH 4的平衡和自生矿物沉淀至关重要。 |
| 关 键 词： | 天然气水合物分解 贫／缺氧甲烷氧化作用 自生碳酸盐岩矿物 化学自养生物 LPTM |
| 文章编号： | 1001-8166(2004)06-0947-08 |
| 修稿时间： | 2003年10月16 |
ADVANCES IN GAS HYDRATE DISSOCIATION AND EFFECTS ON THE ECOLOGY AND ENVIRONMENT |
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| YU Xiao-guo,LI Jia-biao,SOA,Hangzhou ,China.ADVANCES IN GAS HYDRATE DISSOCIATION AND EFFECTS ON THE ECOLOGY AND ENVIRONMENT[J].Advance in Earth Sciences,2004,19(6):947-954. | |
| Authors: | YU Xiao-guo LI Jia-biao SOA Hangzhou China |
| Institution: | Key Labortory of Submarine Geosciences, Second Institute of Oceanography, SOA, Hangzhou 310012,China |
| Abstract: | 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 typicalδ13C 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. |
| Keywords: | Gas hydrate dissociation Global change Anaerobic methane oxidation Authigenic carbonate Chemosynthetic communities LPTM |
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