海洋沉積物是全球最大的甲烷儲庫之一，然而，由於甲烷氧化作用──尤其是厭 氧甲烷氧化作用──對甲烷的消耗，僅有少部分的沉積物甲烷會進入到海水或大氣中。而甲烷氧化作用與其產物對海洋環境碳收支的影響，至今仍是學界密切研究的課 題。本研究企圖透過穩定同位素的標定實驗與環境樣品的分析，去評估甲烷衍生的碳對表層沉積物與底層海水碳庫的貢獻。研究材料乃利用動態影像輔助的採樣工具，於 臺灣西南海域的四方圈合海脊冷泉區中取得。同位素標定實驗顯示該區具有相當活躍 的好氧甲烷氧化作用，潛在速率可達 11.9 μmol L‒1 d‒1。甲烷轉化至不同碳庫的效率由 高至低分別為溶解態無機碳（DIC）、顆粒態有機碳與溶解態有機碳。環境標本分析結果顯示，冷泉區表層沉積物所有的碳庫（DIC、溶解態有機碳與總有機碳）都比背 景站沉積物有較負的穩定碳同位素值，暗示著 13C 含量較低的溶解態碳從硫酸鹽－甲烷轉換帶向上傳輸，並在淺層沉積物被微生物吸收利用。冷泉區的底層海水 DIC 的穩 定碳同位素值相較於背景站海水也偏負 2.5‰。質量平衡計算顯示，甲烷衍生的碳對底層海水只需微小比例（0.2–1.1%）的貢獻就可以對海水 DIC 同位素值造成顯著的影 響。這個初步研究顯示，在海床下數十公分處甲烷氧化作用的產物可以對上方甲烷含量極低的沉積物與底層海水的碳庫造成影響。

Marine sediment is one of the largest methane reservoirs on Earth. Nevertheless, very little of the methane reaches seawater or the atmosphere because of consumption by methane oxidation, especially anaerobic processes, as methane diffuses up through the sediments. How the products of methane oxidation affect carbon budgets in marine environments remains a topic of intensive study. In the present work, we employed two approaches, stable isotope probing experiments and analysis of environmental samples, to assess how methane-derived carbon contributes to the carbon pools in near-surface sediments and bottom seawater. Samples were retrieved from the cold-seep region of the Four-Way Closure Ridge offshore SW Taiwan with video-assisted sampling tools. The stable isotope probing experiments revealed strong aerobic methane oxidizing activities with a potential rate of 11.9 μmol L‒1 d‒1. The conversion efficiency of methane into other carbon pools decreased in the order of dissolved inorganic carbon (DIC)>dissolved organic carbon>particulate organic carbon. Analysis of environmental samples showed that the near-surface sediment at the seep site had substantial 13C-depletion in all carbon pools (DIC, dissolved organic carbon, and total organic carbon) compared to the reference site sediment, indicating microbial uptake of 13C-depleted dissolved carbon ascending from the underlying sulfate-methane transition zone. The bottom seawater of the seep site also had DIC 2.5‰ more depleted in 13C than that of the reference site. Mass balance calculation showed that a small fraction (0.2–1.1%) of methane-derived DIC was enough to account for the 13C depletion. These preliminary results suggest that the products generated by methane-oxidizing processes occurring tens of centimeters below seafloor can affect the carbon pools in the overlying, methane-deficient sediment and bottom water.

審定書 i
致謝 ii
摘要 iii
Abstract v
Contents vii
Figures ix
Tables xi
1. Introduction 1
2. Materials and methods 9
2.1. Site description 9
2.2. Sample collection 9
2.3. Stable isotope probing experiments 12
2.4. Analytical procedures 13
2.5. Instrumentation 16
3. Results 21
3.1. Biogeochemistry of the sediment 21
3.2. Biogeochemistry of the deep and bottom seawater 23
3.3. Dynamics of the carbon pools in the stable isotope probing experiments 23
4. Discussion 31
4.1. Propagation of methane-C in an AeOM community inferred by SIP 31
4.2 Contribution of methane-derived C to carbon pools in the surface sediment 35
4.3 Contribution of methane-derived C to carbon pools in the bottom seawater 38
5. Conclusions 49
References 51
Appendix 55

Barnes, R. O., & Goldberg, E. D. (1976). Methane production and consumption in anoxic marine sediments. Geology, 4, 297-300.
Bender, M. M. (1968). Mass spectrometric studies of carbon 13 variations in corn and other grasses. Radiocarbon, 10, 468-472.
Berndt, C. (2013). TAIFLUX: Fluid and gas migration in the transition from a passive to an active continental margin off SW Taiwan, 02.04.-02.05. 2013, Kaohsiung-Kaohsiung (Taiwan). RV SONNE Fahrtbericht/Cruise Report SO227.
Berger, W. H., Smetacek, V., & Wefer, G. (1989). Ocean productivity and paleoproductivity - an overview. In Productivity of the Oceans present and past: Report of the Dahlem Workshop on Productivity of the Ocean, Berlin, 1988. W. H. Berger, V. S. Smetacek, & G. Wefer (eds), Life Sciences Research Reports 44, Wiley & Sons, Chichester, pp. 1-34.
Bianchi, T. S., Engelhaupt, E., McKee, B. A., Miles, S., Elmgren, R., Hajdu, S., & Baskaran, M. (2002). Do sediments from coastal sites accurately reflect time trends in water column phytoplankton? A test from Himmerfjärden Bay (Baltic Sea proper). Limnology and Oceanography, 47, 1537-1544.
Boetius, A., Ravenschlag, K., Schubert, C.J., Rickert, D., Widdel, F., Gieseke, A., Amann, R., Jørgensen, B.B., Witte, U., Pfannkuche, O., (2000). A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature 407, 623–626.
Boetius, A., & Wenzhöfer, F. (2013). Seafloor oxygen consumption fueled by methane from cold seeps. Nature Geoscience, 6, 725-734.
Borowski, W. S., Paull, C. K., & Ussler, W. (1996). Marine pore-water sulfate profiles indicate in situ methane flux from underlying gas hydrate. Geology,24, 655-658.
Buffett, B., & Archer, D. (2004). Global inventory of methane clathrate: sensitivity to changes in the deep ocean. Earth and Planetary Science Letters, 227, 185-199.
Cai, W. J., & Sayles, F. L. (1996). Oxygen penetration depths and fluxes in marine sediments. Marine Chemistry, 52, 123-131.
Carpenter, R., Bennett, J. T., & Peterson, M. L. (1981). 210Pb activities in and fluxes to sediments of the Washington continental slope and shelf. Geochimica et Cosmochimica Acta, 45, 1155-1172.
Chen, S. C., S. K. Hsu, Y. Wang, C. H. Tsai. (2012). Active mud volcanoes and potential gas hydrate in the upper Kaoping slope offshore SW Taiwan. Mining & Metallurgy, 219, 73-88.
Chi, W. C., Reed, D. L., Liu, C. S., & Lundberg, N. (1998). Distribution of the bottom-simulating reflector in the offshore Taiwan collision zone. Terr. Atmos. Ocean. Sci, 9, 779-794.
Chuang, P. C., Dale, A. W., Wallmann, K., Haeckel, M., Yang, T. F., Chen, N. C., ... & Chung, S. H. (2013). Relating sulfate and methane dynamics to geology: Accretionary prism offshore SW Taiwan. Geochemistry, Geophysics, Geosystems, 14, 2523-2545.
Coffin, R. B., Osburn, C. L., Plummer, R. E., Smith, J. P., Rose, P. S., & Grabowski, K. S. (2015). Deep Sediment-Sourced Methane Contribution to Shallow Sediment Organic Carbon: Atwater Valley, Texas-Louisiana Shelf, Gulf of Mexico. Energies, 8, 1561-1583.
Fry, B. (2006). Stable isotope ecology. Springer Science & Business Media.
Hinrichs, K. U., & Boetius, A. (2003). The anaerobic oxidation of methane: new insights in microbial ecology and biogeochemistry. In Ocean Margin Systems. Wefer, G., Billet, D., Hebbeln, D., Jorgensen, B. B., Schlüter, M., & Van Weering, T. C. (2013). Springer Berlin Heidelberg, pp. 457-477.
Hinrichs, K.-U., Hayes, J.M., Sylva, S.P., Brewer, P.G., DeLong, E.F., (1999). Methane-consuming archaebacteria in marine sediments. Nature 398, 802–805.
House, C. H., Schopf, J. W., & Stetter, K. O. (2003). Carbon isotopic fractionation by Archaeans and other thermophilic prokaryotes. Organic Geochemistry, 34, 345-356.
Hung, C. W. (2015). Estimation of methane flux with modified sampling methods from offshore Southwestern Taiwan. Master thesis, Department of Oceanography, National Sun Yat-sen University, 76 p.p. (In Chinese with English abstract)
Jegen, M., Hölz, S., Swidinsky, A., Sommer, M., Berndt, C., & Chi, W. C. (2014). Electromagnetic and seismic investigation of methane hydrates offshore Taiwan—The Taiflux experiment. In OCEANS 2014-Taipei, Taipei, Taipei.
Joye, S. B., Boetius, A., Orcutt, B. N., Montoya, J. P., Schulz, H. N., Erickson, M. J., & Lugo, S. K. (2004). The anaerobic oxidation of methane and sulfate reduction in sediments from Gulf of Mexico cold seeps. Chemical Geology, 205, 219-238.
Komada, T., Burdige, D. J., Crispo, S. M., Druffel, E. R., Griffin, S., Johnson, L., & Le, D. (2013). Dissolved organic carbon dynamics in anaerobic sediments of the Santa Monica Basin. Geochimica et Cosmochimica Acta, 110, 253-273.
Krummen, M., Hilkert, A. W., Juchelka, D., Duhr, A., Schlüter, H. J., & Pesch, R. (2004). A new concept for isotope ratio monitoring liquid chromatography/mass spectrometry. Rapid Communications in Mass Spectrometry, 18, 2260-2266.
Kvenvolden, K. A. (1989). Methane hydrates and global climate. Global Biogeochemical Cycles, 2.
Liu, C. S., Schnürle, P., Wang, Y. S., Chung, S. H., Chen, S. C., & Hsiuan, T. H. (2006). Distribution and characters of gas hydrate offshore of southwestern Taiwan. Terrestrial, Atmospheric and Oceanic Sciences, 17, 615-644.
Liu, P. C. (2015). Stable-isotope Probing of Methanotrophs and Methylotrophs Offshore Southwestern Taiwan. Master thesis, Institute of Oceanography, National Taiwan University, 125 p.p. (In Chinese with English abstract)
MacDonald, I. R., Reilly Jr, J. F., Best, S. E., Venkataramaiah, R., Sassen, R., Guinasso Jr, N. L., & Amos, J. (1996). Remote sensing inventory of active oil seeps and chemosynthetic communities in the northern Gulf of Mexico. The American Association of Petroleum Geologists, 27-37.
Milkov, A. V. (2004). Global estimates of hydrate-bound gas in marine sediments: how much is really out there? Earth-Science Reviews, 66(3), 183-197.
Niewöhner, C., Hensen, C., Kasten, S., Zabel, M., & Schulz, H. D. (1998). Deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off Namibia. Geochimica et Cosmochimica Acta, 62, 455-464.
Op den Camp, H. J., Islam, T., Stott, M. B., Harhangi, H. R., Hynes, A., Schouten, S. & Dunfield, P. F. (2009). Environmental, genomic and taxonomic perspectives on methanotrophic Verrucomicrobia. Environmental Microbiology Reports, 1, 293-306.
Pohlman, J. W., Bauer, J. E., Waite, W. F., Osburn, C. L., & Chapman, N. R. (2011). Methane hydrate-bearing seeps as a source of aged dissolved organic carbon to the oceans. Nature Geoscience, 4, 37-41.
Reeburgh, W. S. (2007). Oceanic methane biogeochemistry. Chemical Reviews, 107, 486-513.
Reitner, J., Peckmann, J., Reimer, A., Schumann, G., & Thiel, V. (2005). Methane-derived carbonate build-ups and associated microbial communities at cold seeps on the lower Crimean shelf (Black Sea). Facies, 51, 66-79.
Roberts, H. H., & Carney, R. S. (1997). Evidence of episodic fluid, gas, and sediment venting on the northern Gulf of Mexico continental slope. Economic Geology, 92, 863-879.
Ryan, P. R. (1984). Deep-sea hot springs and cold seeps. Oceanus, 27, 32-33.
Sager, W. W., MacDonald, I. R., & Hou, R. (2004). Side-scan sonar imaging of hydrocarbon seeps on the Louisiana continental slope. AAPG Bulletin, 88, 725-746.
Schnurle, P. H. I. L. I. P. P. E., Hsiuan, T. H., & Liu, C. S. (1999). Constraints on free gas and gas hydrate bearing sediments from multi-channel seismic data, offshore Southwestern Taiwan. Petroleum Geology of Taiwan, 33, 21-42.
Schoell, M. (1988). Multiple origins of methane in the earth. Chemical geology, 71, 1-10.
Smith, B. N., & Epstein, S. (1971). Two categories of 13C/12C ratios for higher plants. Plant physiology, 47, 380-384.
Solomon, E. A., Kastner, M., MacDonald, I. R., & Leifer, I. (2009). Considerable methane fluxes to the atmosphere from hydrocarbon seeps in the Gulf of Mexico. Nature Geoscience, 2, 561-565.
Sommer, S., Pfannkuche, O., Linke, P., Luff, R., Greinert, J., Drews, M., & Viergutz, T. (2006). Efficiency of the benthic filter: Biological control of the emission of dissolved methane from sediments containing shallow gas hydrates at Hydrate Ridge. Global Biogeochemical Cycles, 20(2), doi: 10.1029/2004GB002389.
Stocker, T. F., Qin, D., Plattner, G. K., Tignor, M., Allen, S. K., Boschung, J. & Midgley, B. M. (2013). IPCC, 2013: climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change.
Teng, L. S. (1990). Geotectonic evolution of late Cenozoic arc-continent collision in Taiwan. Tectonophysics, 183, 57-76.
Thauer, R. K. (1998). Biochemistry of methanogenesis: a tribute to Marjory Stephenson. Microbiology, 144, 2377-2406.
Ver, L. M. B., Mackenzie, F. T., & Lerman, A. (1999). Carbon cycle in the coastal zone: effects of global perturbations and change in the past three centuries. Chemical Geology, 159, 283-304.
Valentine, D. L., Blanton, D. C., Reeburgh, W. S., & Kastner, M. (2001). Water column methane oxidation adjacent to an area of active hydrate dissociation, Eel River Basin. Geochimica et Cosmochimica Acta, 65, 2633-2640.
Valentine, D. L., Kastner, M., Wardlaw, G. D., Wang, X., Purdy, A., & Bartlett, D. H. (2005). Biogeochemical investigations of marine methane seeps, Hydrate Ridge, Oregon. Journal of Geophysical Research: Biogeosciences, 110, doi: 10.1029/2005JG000025.
Whiticar, M. J. (1999). Carbon and hydrogen isotope systematics of bacterial formation and oxidation of methane. Chemical Geology, 161, 291-314.
Wollast, R. (1991). The coastal organic carbon cycle: fluxes, sources and sinks. In Ocean margin processes in global change. pp. 365-381.
Yoshinaga, M. Y., Holler, T., Goldhammer, T., Wegener, G., Pohlman, J. W., Brunner, B., & Elvert, M. (2014). Carbon isotope equilibration during sulphate-limited anaerobic oxidation of methane. Nature Geoscience, 7, 190-19.