2006-01-012024-05-17https://scholars.lib.ntu.edu.tw/handle/123456789/671576摘要：本研究可分為四個部份：(1) Passive margin精查採樣區域之11個測站活塞沉積物樣品之分析，其中包括2站由新研發之18米長活塞岩心採集器所採集，並成功採集到破過去海研一號採樣記錄之10米長岩心，藉由沉積體系內硫酸鹽還原作用在甲烷水合物影響下之變化程度及甲烷與硫酸鹽還原作用之密切關係來探討台灣西南海域passive margin區域甲烷水合物賦存之可能性；(2) Active及passive margin交界區之普查採樣之22個測站2米重力沉積物樣品之分析，藉由大面積的普查採樣，比較passive margin與active margin甲烷與硫酸鹽還原作用之差異，期望能尋找了解甲烷水合物在何種環境下有最佳的生成與保存條件；(3) 利用新購置的海底拖曳照相系統於測站G23、96及GS5進行9條測線之海床拍攝工作，以瞭解海底地貌構造（vent、authigenic carbonate）及海底生物群聚種類（bivalves、bacterial mats）之分佈；(4) 完成MD第四根岩心之分析工作，以瞭解四根MD岩心的差異性，進一步探討天然氣水合物存在的可能性及生成條件。 研究分析項目包括間隙水溶解硫化氫、硫酸鹽、氯離子濃度與沉積物pyrite-S、AVS、有機碳、碳酸鈣含量及含水量等項目。 研究結果顯示，passive margin研究區域硫酸鹽還原作用明顯比active margin較慢，除了測站GS5之外，大部份測站硫酸鹽濃度於採樣深度內皆大於15mM。根據EK500之探測資料顯示，測站GS5水體中呈現一明顯之Flare現象，顯示此測站有流體從沉積物中往上層水體冒出，為一active vent。因此GS5測站之間隙水硫酸鹽濃度呈現非常快速的降低，於40公分即已遞減至6mM，溶解硫化氫濃度亦高達18mM之高值，且沉積物pyrite-S含量隨深度增加，於40公分含量可高達160mole/g之高值。此岩心中含有大量貝殼碎片，使碳酸鈣含量亦可高達60%。GS3則於300cm之後突然出現高含量的pyrite-S（220mole/g），推測此測站在過去曾是一冒氣區。而10米長岩心之測站GS11A之硫酸鹽濃度亦從表層之27mM隨深度遞減至10米之6mM左右，但未發現有大量的硫化物產生。 普查研究發現澎湖水道以西的區域間隙水硫酸鹽濃度隨深度增加呈現明顯遞減的趨勢，硫酸鹽遞減梯度介於-0.0168至-0.0954 mM/cm之間，SMI深度介於300至1800公分之間，且有5個測站之硫酸鹽遞減梯度高於-0.08 mM/cm以上（SMI小於400cm），顯示此區域部份測站含有較高的硫酸鹽還原速率。 海底拖曳照相系統於測站GS5海底發現了許多mussels及螃蟹的生長，而mussels的豐度每平方公尺最高可超過380隻以上。這是本研究首次發現如此大量活體的生物聚集在海床上生長，顯示測站GS5仍是一active的venting區域。本研究更於96測站採集到了2隻活的clams樣品，目前仍在進行種屬的確認。 本研究亦針對上年度MD船所採樣的四站岩心樣品進行更深入的分析研究工作，如間隙水鈉、鉀、鎂、鈣及18O與沉積物無機碳13C、18O之分析。研究結果顯示，間隙水18O介於-0.3~0.4&#8240;之間，變化頗大。此外，MD05-2911岩心之21.5米出現非常輕的無機碳13C及重18O的值，此異常輕的無機碳13C明顯為自生性碳酸鈣的特徵，顯示可能存在gas hydrate而造成甲烷厭氧氧化反應，產生較輕的碳酸根離子，而進一步形成13C異常輕的自生性碳酸鈣沉積。 本研究於本年度在沉積物硫化物與碳酸鈣碳氧同位素之分析皆有較往年有所突破與發現，更於TowCam航次中拍攝及採集到許多天然氣水合物存在的特徵，並積極進行沉積物碳酸鈣碳氧同位素與硫同位素之測定，這將提供更多有利的證據及數據資料，來探討台灣西南海域天然氣水合物存在的可能與形成機制。 <br> Abstract: Sulfate reduction is a useful proxy in examines degree of methane migration and diagenetic reactions in sediments. In this report, we study sulfate reduction in the active and passive margin sediments. Three different sampling approaches were employed in this study, gravity coring of the reconnaissance survey, box core and short and long piston coring of the detail survey as well as TowCam survey in three cruises (OR1-792, 804 and 810). A total of 9 (<6 m) piston cores, 2 long piston cores (>6 m), 11 box cores, 22 gravity cores, 7 grab samples and 8 TowCam survey. Pore water sulfate, dissolved sulfide, chloride together with sediment pyrite, organic carbon, carbonate carbon were analyzed. 13C and 18O were also analyzed for authigenic carbonate and bivalve shells. The result showed that large differences of sulfate reduction were observed between passive and active margin sediments. In general, rapid sulfate reductions were found in active margin while slower in passive margin. However, very rapid sulfate reductions were found in some active venting area in the passive margin sediments. At site GS5, flare feature appeared in the water column as well as rapid sulfate reduction in sediments. Within 40 cm beneath sediment/water interface, dissolved sulfide reached 18 mM and pyrite reached 160 mole/g. In addition, authigenic carbonate with low 13C was also found in this site. Towcam survey also showed that life venting existed in site GS5. Abundant live mussels, crabs were found at the fracture surface of the authigenic carbonate slabs. The population of live mussels can reach 380 specimens per square meter. As a comparison, abundant bivalves, different species as compare to GS5, were found at G23. In addition, large carbonate blocks were found in site G23 as compare to GS5 where mostly carbonate slabs were found. The abundant bivalves, crabs and authigenic carbonate demonstrate that active venting occurred in the study area.