台灣東部雷公火泥火山之碳循環

Abstract

厭氧型甲烷氧化作用 (Anaerobic Oxidation of Methane, AOM) 在甲烷供應充足的厭氧環境中已被廣泛發現，其中海底泥火山和滲流系統的研究發現沈積層中總有機碳和溶解有機碳含量和穩定碳同位素組成在 AOM 作用深度範圍內有明顯變化，因此推論AOM 作用不僅消耗來自深處的甲烷並形成冷泉碳酸鹽的堆積，也製造有機碳進入孔隙水和沈積物中，形成特殊的碳循環路徑，將老碳轉換成其他生物可以使用的能源。 相較於海域泥火山和滲流系統，陸域泥火山的 AOM 作用研究十分缺乏，而以甲烷為主要成份的台灣東部雷公火泥火山，已經利用地球化學和分子生物分析，證實此處普遍存在與鐵還原合作的AOM作用進行，值得對於其碳循環的特徵進一步探討。因此，本研究分析雷公火泥火山的噴泥與周圍岩芯中溶解態有機碳、無機碳和固態無機碳、有機碳的含量與其穩定碳同位素組成，以期深入了解陸域泥火山中 AOM 和其他微生物在碳循環中扮演的角色。 分析結果顯示在雷公火泥火山的沉積物岩芯中微生物組成複雜且變動頻繁，隨著時間推移和空間變化彼此間差異極大，除了厭氧型甲烷氧化菌和產甲烷菌之外，還有光合作用菌和異營生物同時存在於此，且影響此地的有機碳和無機碳變動。根據岩芯中有機碳含量和其 d13C 值可將此地有機碳累積和消耗的特徵分成三種類型，在不同類型中各種生物的作用及其對於有機碳增減的貢獻程度不一。整體而言，岩芯中不同碳成分在其含量和穩定碳同位素組成受控於生物族群的明顯差異，變動複雜的微生物族群是影響雷公火泥火山中碳循環的關鍵，然而控制生物族群變動的環境因素與調控因子則仍待進一步釐清。

Anaerobic Oxidation of Methane (AOM) has been widely discovered in methane-rich environments. In marine mud volcanoes and cold seep environments, the AOM activity could enhance the quantity and change the isotopic composition of organic and inorganic carbon in pore water and sediments. Apparently, the AOM activity not only consume deep-sourced methane and produce authigenic carbonates, but also transform dead carbon to organic carbon which becomes a new energy sources for other microorganisms. The AOM activity in terrestrial mud volcanoes has not been well studied. Previous geochemical and molecular studies have shown that an iron-coupled AOM occurred in core sediments of Lei-Gong-Huo mud volcano (LGHMV) in eastern Taiwan and furthermore investigation of its characteristics of carbon cycle is expected. In order to reveal the role of AOM and other microbial activities in carbon cycle, the abundance and d13C values of organic/inorganic carbon of bubbling fluid and core sediments were analyzed. The results indicate that the spatial and temporal variations of microbial communities and carbon dymanics are significant in core sediments. Although the AOM plays a critical role in all sampling sites near bubbling pools, other microorganisms, including heterotrophs, phototrophs and methanogens, are also important to overall carbon cycle. The distribution of organic carbon in core sediments can be divided into three types. Each type shows a distinguishable pattern and is contributed by different microbial processes. Overall, the differences in abundance and d13C values of different carbon compounds in core sediments result from the dynamic variation of complexly structured microbial communities. Further evaluation of environmental controls and regulations on microbial communities may provide a clue to deeply understand the carbon cycle in LGHMV.