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Published Papers 【 display / non-display 】

Published Papers 【 display / non-display 】

• Sr isotopic ratios of hydrothermal fluids from the Okinawa Trough and the implications of variation in fluid–sediment interactions

  Tomohiro Toki, Tasuku Nohara, Yoshiaki Urata, Ryuichi Shinjo, Shuko Hokakubo-Watanabe, Jun-ichiro Ishibashi, and Shinsuke Kawagucci

  Progress in Earth and Planetary Science ( Springer Nature )  9 ( 1 ) 59   2022.11 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

  　View Summary

  沖縄トラフにおける海底熱水中のSr同位体比を比較すると，海水の混入を補正しても，海水よりもはるかに高い同位体比を示すことがわかった。このことから，海水よりもはるかに高い固体と反応していることが示唆され，沖縄トラフに供給されている大陸地殻を起源とする粘土鉱物と反応していることが示唆された。こういった高いSr同位体比は，堆積物が被覆している海底熱水系で見られる共通の特徴であると言える。

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• Identification of a large mud volcano field in the Hyuga-nada, northern end of the Ryukyu trench, offshore Japan

  Asada, M; Yamashita, M; Fukuchi, R; Yokota, T; Toki, T; Ijiri, A; Kawamura, K

  FRONTIERS IN EARTH SCIENCE ( Frontiers in Earth Science )  11   2023.11 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  We identified 27 new mud volcanoes, including potential ones, in a part of the Hyuga-nada area, southwest offshore Japan, at the northern end of the Ryukyu Trench, based on subseafloor geological structures using geophysical investigations. These mud volcanoes exhibited high density and breadth and were likely connected to other mud volcano fields in the south. Acoustic investigations indicated subseafloor structures. Multiple acoustically transparent bodies were interpreted as a region containing gas. They were likely to appear along faults and below the bottom of valleys and sometimes reached the seafloor, expressing mud volcanoes onto the seafloor. They also indicated the wide distribution of subseafloor free-gas throughout the area. These acoustic investigations suggested that a swarm of mud volcanoes exists over the Hyuga-nada area, heterogeneously distributed along a series of plate convergent margins, the Nankai Trough, and the northern part of the Ryukyu Trench.

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• Distribution of dissolved methane in seawater from the East China Sea to the Ryukyu forearc

  Toki, T; Chibana, H; Shimabukuro, T; Yamakawa, Y

  FRONTIERS IN EARTH SCIENCE ( Frontiers in Earth Science )  11   2023.11 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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• Assessing the activity of mud volcanism using boron isotope ratios in pore water from surface sediments of mud volcanoes off Tanegashima (SW Japan)

  Mitsutome, Y; Agena, K; Toki, T; Song, KH; Shinjo, R; Ijiri, A

  FRONTIERS IN MARINE SCIENCE ( Frontiers in Marine Science )  10   2023.09 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Mud volcanoes can cause various geohazards, so it is very important to know their activity level and their distribution. Surface sediments were collected from four submarine mud volcanoes (MVs) off Tanegashima (SW Japan), namely, MV1, MV2, MV3, and MV14. We extracted pore water from the surface sediments and investigated its chemical and isotopic compositions. The sodium (Na) and chloride (Cl^-) concentrations decreased and the boron (B) and lithium (Li) concentrations increased with increasing depth, suggesting that some fluids with lower Na and Cl^- concentrations and higher B and Li concentrations than seawater were supplied upward from the deep sub-seafloor. The fluid advection velocities estimated from the pore-water profiles differed for each MV, and those of MV3 were the fastest (14 cm/yr) in this study. The estimated equilibrium temperature with clay minerals using Na and Li concentrations were 93-134°C, corresponding to the temperature of environments around 3.7 to 5.3 km below the seafloor. This indicates that these components originated from these depths and that the origin depth did not reach the plate boundary in this area. The B isotope ratio in the pore water was extremely high up to +57 ‰, suggesting that it was strongly affected by adsorption onto the surface of the sediments. A higher B isotope ratio (+57 ‰) was detected in MV3, which was considered to be more active, indicating that more B was adsorbed onto clay minerals supplied from deeper depths.

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• Origins of sediments and fluids in submarine mud volcanoes off Tanegashima Island, northern Ryukyu Trench, Japan

  Ijiri, A, Setoguchi, R, Mitsutome, Y, Toki, T, Murayama, M, Hagino, K, Hamada, Y, Yamagata, T, Matsuzaki, H, Tanikawa, W, Tadai, O, Kitada, K, Hoshino, T, Noguchi, T, Ashi, J, Inagaki, F

  Front. Earth Sci. ( Frontiers in Earth Science )  11   2023.06 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Mud volcanoes are topographic features through which over-pressurized sediments are intruded upward and erupted, transporting fluids and sediments from the deep subsurface to the surface/seafloor. To understand material and biogeochemical cycling through mud volcanoes, we investigated the origins of sediments and fluids erupted by four submarine mud volcanoes off Tanegashima Island, along the northern Ryukyu Trench: MV#1–3 and MV#14. We estimated the ages of the source sequences of the mud volcano sediments to be middle to late Miocene based on nannofossils and ¹⁰Be ages. The sediments were characteristically enriched in illite. The similar mineral compositions and vitrinite reflectance values (0.42%–0.45%) of sediments erupted by the mud volcanoes strongly suggest that each is rooted in the same source sequence. Pore waters had Cl⁻ concentrations ∼40% that of seawater and were proportionally enriched in ¹⁸O and depleted in D, indicating the addition of freshwater from the dehydration of clay minerals. However, the smectite and illite contents (<40%) in the clay size fraction ruled out in situ smectite dewatering as the cause of the pore water Cl⁻ dilution. Thus, fluids derived from clay dewatering must have originated from deeper than the source sequence of the mud volcano sediments. Vertical Cl⁻ profiles indicate that the upward fluid advection rate and eruption frequency decrease from MV#3 to MV#2, MV#1, and MV#14 (MV#14 being dormant). At the active mud volcanoes, the C₁/C₂ ratios (<100) and methane δ¹³C values (−56‰ to −42‰) indicate that hydrocarbon gases are mostly derived from the thermal decomposition of organic matter in deep sediments where the in situ temperature exceeds 80°C. At the dormant MV#14, high C₁/C₂ ratios (700–4,000) and low methane δ¹³C values (ca. −75‰) suggest the limited supply of thermogenic methane and the subsequent shallow methanogenesis. Because vitrinite reflectance values indicate that the source sediments are too immature to produce thermogenic hydrocarbons, the hydrocarbon gases, like the fluids derived from clay dewatering, were probably supplied from deeper than the source strata. The supply of deep fluids into the source sequence might be a universal phenomenon in subduction zones, and may play an important role in mud volcanism and associated biogeochemical cycling.

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Books 【 display / non-display 】

Books 【 display / non-display 】

• Nature in the Ryukyu Archipelago

  Tomohiro Toki ( Part: Single Author ,  When do you research hydrothermal systems? Now! )

  Change and Coral Reef/Island Dynamics Faculty of Science, University of the Ryukyus  2015

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  沖縄トラフの海底熱水研究の最新トピックをわかりやすく英語で紹介。

• Deep-sea Life - Biological observations using research submersibles

  Jun-ichiro Ishibashi, Tomhiro Toki ( Part: Multiple Authorship )

  Tokai University Press  2008.02

Other Papers 【 display / non-display 】

Other Papers 【 display / non-display 】

• Contribution and mission of geochemistry to mud volcano study

  Tomohiro Toki

  Bulletin of the Faculty of Science, University of the Ryukyus ( Faculty of Science, University of the Ryukyus )  ( 108 ) 1 - 26   2020.03

   

• 多良間海丘熱水活動域での鉄利用微生物の解明

  牧田寛子, 毛利諒子, 坂本貴大, 鈴木優美, 鹿島裕之, 宮崎淳一, CHEN Chong, 松井洋平, 吉梅剛, 山中寿朗, 倉場可織, 横田瑛里, 岡村慶, 野口拓郎, 中村謙太郎, 土岐知弘, 崎山智彦, 橋本泰志, 高村岳樹, 高井研

  ブルーアース要旨集   2018   88   2018

   

  J-GLOBAL

• 地質調査で採取された堆積物試料中の間隙水の地球化学的解析

  石橋純一郎, 正木裕香, 岡村慶, 野口拓郎, 土岐知弘, 新城竜一

  SIP 『次世代海洋資源調査技術』(海のジパング計画) 海底熱水鉱床の調査技術プロトコル     2017

   

• Simple method of collecting pyrolysis gas from bagasse

  Ryo Itou, Keiko Nakasone, Tomohiro Toki

  Bulletin of the Faculty of Science, University of the Ryukyus ( Faculty of Science, University of the Ryukyus )  ( 102 ) 1 - 11   2016.09

   

• Community structure of a microbial mat from the methane seep off Yagaji Island

  Tomohiro Toki, Hisako Hirayama, Syogo Oshima

  Bulletin of the Faculty of Science, University of the Ryukyus ( Faculty of Science, University of the Ryukyus )  ( 100 ) 5 - 12   2015.09

   

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Presentations 【 display / non-display 】

Presentations 【 display / non-display 】

• A Future-Oriented Trial Using Board Games Produced by Residents on Yoron Island

  Toki Tomohiro, Shimabukuro Miyuki, Shimabukuro Hitoshi, Kubo Yoshiaki

  Proceeding of Annual Conference  2023  -  2023 

  CiNii Research

• Cold axis or Hot axis? Investigating the geothermal structure of a pre-break-up backarc basin, southern part of Okinawa Trough

  Otsubo Makoto, Arai Ryuta, Toki Tomohiro, Kinoshita Masataka, Misawa Ayanori, Oohashi Kiyokazu, Kubota Yoshimi, Miyakawa Ayumu, Ikegami Fumihiko, Regalla Christine, Su Chih-Chieh

  Annual Meeting of the Geological Society of Japan  2022  -  2022 

  CiNii Research

• The roots of helium in surface sediments of submarine mud volcanoes off Tanegashima

  Yuki Mitsutome, Tomohiro Toki, Takanori Kagoshima, Naoto Takahata, Yuji Sano, Yama Tomonaga, Akira Ijiri

  AGU Fall Meeting 2021  (New Orleans, LA & Online Everywhere)  2021.12  -  2021.12 

• Roots and reservoir of venting fluid at Taketomi submarine hot spring

  Tomohiro Toki, Ryuichi Shinjo, Yuki Mitsutome, Syogo Oushima, Harue Masuda, Akira Ijiri, Shinji Nakaya

  AGU Fall Meeting 2021  (New Orleans, LA & Online Everywhere)  2021.12  -  2021.12 

• Origin of helium in surface sediments of submarine mud volcanoes off Tanegashima Island

  Yuki Mitsutome, Tomohiro Toki, Takanori Kagoshima, Yuji Sano, Tomonaga Yama

  The University of Tokyo Earthquake Research Institute Joint Research Meeting "Cross-sectional Study on Trench Seaward Processes: Toward Elucidation of Subduction Zone Inputs"  (Online (Zoom))  2021.10  -  2021.10 

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Grant-in-Aid for Scientific Research 【 display / non-display 】

Grant-in-Aid for Scientific Research 【 display / non-display 】

• Grant-in-Aid for Scientific Research(C)

  Project Year: 2023.04  -  2027.03 

  Direct: 3,600,000 (YEN)  Overheads: 4,680,000 (YEN)  Total: 1,080,000 (YEN)

• Fluid flow in the uppermost part of the incoming plate seaward of the trench: Regional variations and influence on processes around the plate interface

  Grant-in-Aid for Scientific Research(B)

  Project Year: 2023.04  -  2026.03 

  Direct: 14,400,000 (YEN)  Overheads: 18,720,000 (YEN)  Total: 4,320,000 (YEN)

• Construction of a model for the diffusion and circulation of deep subsurface life and carbon to the ocean via submarine mud volcanism

  Grant-in-Aid for Scientific Research(B)

  Project Year: 2020.04  -  2023.03 

  Direct: 13,500,000 (YEN)  Overheads: 17,550,000 (YEN)  Total: 4,050,000 (YEN)

• Construction of a model for the diffusion and circulation of deep subsurface life and carbon to the ocean via submarine mud volcanism

  Grant-in-Aid for Scientific Research(B)

  Project Year: 2020.04  -  2023.03 

  Direct: 13,500,000 (YEN)  Overheads: 17,550,000 (YEN)  Total: 4,050,000 (YEN)

• Construction of a model for the diffusion and circulation of deep subsurface life and carbon to the ocean via submarine mud volcanism

  Grant-in-Aid for Scientific Research(B)

  Project Year: 2020.04  -  2023.03 

  Direct: 13,500,000 (YEN)  Overheads: 17,550,000 (YEN)  Total: 4,050,000 (YEN)

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Other External funds 【 display / non-display 】

Other External funds 【 display / non-display 】

• Project Name: Research Project

  Project Year: 2019.04  -  2027.03 

  Offer Organization: Research Institute for Humanity and Nature

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