| 摘要: |
| 利用化学和稳定同位素化学等方法分析研究区沉积物间隙水甲烷和硫酸根、pH 和ΣCO2 以及δ13C-CH4 和δ13C-ΣCO2 的垂直剖面分布。结果显示, 间隙水硫酸根浓度呈线性梯度减小, 至沉积物甲烷-硫酸盐界面(sulfate-methane interface, SMI)附近, 硫酸盐几乎全部消耗而甲烷浓度急剧增大;与此同时,间隙水pH 和ΣCO2 在该深度位置明显升高。间隙水地球化学特征揭示了沉积物发生了AOM 作用。在AOM 过程中,由于12CH4 氧化速率较13CH4 快, 故引起沉积物间隙水剩余甲烷的碳同位素偏重, 而δ13C-ΣCO2值变为极负.珠江口QA11-2、QA12-9、QA12-14 和GS-1 四个站位SMI 对应深度分别为12cm、38cm、50cm 和204cm, 而南海BD-7 站位由间隙水硫酸根剖面变化推算约为600cm。从珠江河口到南海沉积物, 由于受陆源输入的减少, 表层沉积物有机质含量呈降低趋势。有机质输入量及其活性的高低是制约了沉积物SMI 分布深浅的关键因素, 这是由于高含量的活性有机质一方面可加速间隙水硫酸根通过有机质再矿化分解作用途径消耗; 另一方面可引起向上扩散进入AOM 反应带的甲烷通量增大, 使得通过AOM 作用的硫酸根消耗通量相应增大, 其结果造成沉积物SMI 的上移。根据沉积物C/N 比值以及13C 剖面变化, 推断AOM 作用的可能发生机制是由于在沉积物表层再矿化作用过程中, 因一部分活性有机质被大量消耗, 导致进入沉积物硫酸根还原带底部的活性有机质数量相应减少, 从而引起部分硫酸根转为与甲烷发生反应, 并在微生物的作用下完成AOM 过程。
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| 关键词: 沉积物间隙水, 硫酸根还原, 甲烷厌氧氧化(AOM), 甲烷-硫酸根界面(SMI) |
| DOI：10.11693/hyhz200903001001 |
| 分类号: |
| 基金项目:国家自然科学基金资助项目, 40803020 号, 同济大学海洋地质重点实验室开放基金项目, MG023 号 |
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| DEPTH OF SULFATE-METHANE INTERFACE (SMI) IN SEDIMENT AND AFFECTING FACTORS IN THE PEARL RIVER ESTUARY AND VICINAL SOUTH CHINA SEA |
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WU Zi-Jun1,2, ZHOU Huai-Yang1, PENG Xiao-Tong1
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1.State Key Laboratory of Marine Geology, Tongji University;2.School of Earth and Space Sciences,University of Science and Technology
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| Abstract: |
| The concentrations of CH4 and SO42? in pore water and the carbon isotope compositions of total dissolved inorganic (ΣCO2) and CH4 were determined for five sedimentary cores collected from Pearl River estuary and vicinal region of the South China Sea. Results show that the sulfate concentration decreased linearly and the methane concentration increased dramatically near sulfate-methane interface (SMI) in all stations. The geochemical profiles of pore water have showed indirect evidence of anaerobic oxidation of methane (AOM). In the process of AOM, 12CH4 was oxidized faster than 13CH4, and this caused the enrichment in residual methane δ13C and δ13C-ΣCO2 minimum. The SMI at stations QA11-2,QA12-9,QA12-14 and GS-1 occurred at 12cm, 38cm,50cm, and 204 cm in depth, respectively, while that at station BD-7 was about 600 cm inferred from the sulfate concentrations in sediments. The depths of SMI are controlled by the type and amount of the sedimentary organic matter. Abundant organic material would speed up the depletion of sulfate via sedimentary organic matter degradation, cause increase in methane flux across SMI, and further result in reduction of some sulfate by AOM. Accordingly, the depth of SMI shifted towards the sediment surface. The C/N ratio and 13C profile in sediment of Station GS-1 depict a possible scenario of AOM: sediment diagenesis/remineralization consumed a large amount of labile organic matter (mainly alga-derived), reduced the amount of the organic matter entering the base of sulfate reduction zone, and then partial sulfate was in turn consumed in the reaction with methane due to the scarcity of labile organic matter.
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| Key words: Sediment pore water, Sulfate reduction, Anaerobic oxidation of methane (AOM), Sulfate-methane interface (SMI) |
