Relationship between Sulfate Reduction and Methane Migration in Sediments offshore Southwestern Taiwan

本研究目的在於探討台灣西南海域硫酸鹽還原和黃鐵-硫(pyrite)的形成與甲烷形成與擴散之關係。異常快速的硫酸鹽還原深受甲烷擴散遷移的影響。分析項目包括間隙水之硫化氫及硫酸鹽濃度、沉積物之有機碳、碳酸鈣及黃鐵-硫含量。 硫酸鹽還原、甲烷濃度、硫化氫濃度及黃鐵-硫含量在本研究區域有明顯差異。硫酸鹽在1公尺處即遞減為零並伴隨有高濃度甲烷。此外，硫化氫濃度高達9689μM，黃鐵-硫含量也高至331μmole/g。但是在本研究區域有機碳含量並不高，低於1.0%。 本研究區域甲烷及硫酸鹽通量在水深700-1500公尺的測站皆有相當高的值。硫酸鹽還原深受下層甲烷向上擴散之影響。所以，在有高甲烷通量的測站皆有發現到有高含量的黃鐵-硫。然而下層向上擴散之甲烷並不是主要控制異常快速硫酸鹽還原之因素。在本研究區域異常快速硫酸鹽還原不但受下層甲烷往上擴散之影響，上層水體有機碳之快速沉降也影響硫酸鹽還原作用。This study investigated sulfate reduction and iron sulfide mineral formation in sediments offshore southwestern Taiwan. Special emphasis is placed on sulfate reduction under the influence of methane migration. Analytical works include pore water hydrogen sulfide, sulfate and sediment for organic carbon, carbonate, AVS(acid volatile sulfide) and pyrite-S. Large degree of variations for sulfate reduction, methane, dissolved sulfide, and sulfide minerals concentrations were observed. A complete depletion of sulfate as shallow as 1m was found together with high concentration of methane. Furthermore, dissolved sulfide as high as 9689μM with pyrite reaching 331μmole/g were also observed in the region but organic carbon concentrations remain relatively low with value no more than 1.0%. Even though large variations were found for a number of measured parameters, pyrite concentrations, calculated methane and sulfate flux showed a distinctly high at water depth between 700-1500m.Sulfate reduction in the study region sediments is strongly controlled by the methane migration with downward sulfate flux linearly correlated with upward methane flux. As a result, more pyrite were found in region with high methane flux.However, upward methane migration is not the sole controlling factor for the observed high sulfate reduction.The observed high sulfate reduction is most likely a combine effect of high sedimentation rate as well as high methane flux.目 錄 英文摘要………………………………………..………….……...Ⅰ 中文摘要…………………………………………………….……...Ⅱ 目錄……………………………………………………….………...i 圖目錄……………………………………………………….……...ii 表目錄…………………………………………………...…….…...v 第一章 緒論…………………………………………………………….. 1-1 海洋沉積物之硫酸鹽還原作用………………………….….1 1-2 海洋沉積物之自生硫化鐵成………………………………..3 1-3 研究動機與目的…………………………………….…….…5 第二章 樣品採集與分析方法……………………...……………...8 2-1 樣品採集……………………………………………………..8 2-1-1 採集位置……………………………………….…….8 2-1-2 採樣方法……………………………………….…….8 2-2 樣品前處理……………………………………………….….8 2-3 分析方法…………………………………….……………….9 2-3-1 間隙水硫酸鹽濃度……………………………......9 2-3-2 間隙水溶解硫化氫濃度……………………….…...10 2-3-3 沉積物有機碳及碳酸鈣含量…………………...….10 2-3-4 沉積物硫化鐵礦物含量……………………….…...11 第三章 結果………………….…………………………………..18 3-1 沉積物有機碳及碳酸鈣…………………………………...18 3-2 間隙水硫酸鹽及溶解硫化氫……………………………...19 3-3 沉積物硫化礦物…………………………………………....20 第四章 討論…………………………….………………………..37 4-1 區域性變化與水深之關係…………………………….…...37 4-2 C/S比值與沉積環境之關係…………………………….….39 4-3 硫酸鹽通量與甲烷通量之關係……………………….…...40 第五章 結論…………….………………………………………..54 參考文獻………………….…………………………………….……5