Toki Tomohiro

写真a

Title

Associate Professor

Researcher Number(JSPS Kakenhi)

50396925

Homepage URL

http://www.cc.u-ryukyu.ac.jp/~toki/index.html

27 15 2 2 16 27 16
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Current Affiliation Organization 【 display / non-display 】

  • Duty   University of the Ryukyus   Faculty of Science   Chemistry, Biology and Marine Science   Associate Professor  

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University 【 display / non-display 】

  • 　
    -
    1999.03

    The University of Tokyo   Faculty of Science   Department of Chemistry   Graduated

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Graduate School 【 display / non-display 】

  • 　
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    2001.03

    The University of Tokyo  Graduate School, Division of Natural Science  Master's Course  Completed

  • 　
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    2004.03

    Hokkaido University  Graduate School, Division of Natural Science  Division of Earth and Planetary Sciences  Doctor's Course (second term)  Completed

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Academic degree 【 display / non-display 】

  • Hokkaido University -  Doctor of Science

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External Career 【 display / non-display 】

  • 2007.04
    -
    2015.04

    University of the Ryukyus, Faculty of Science, Department of Chemistry, Biology, and Marine Science, Chemistry Program, Research Associate  

  • 2015.05
    　
    　

    University of the Ryukyus, Faculty of Science, Department of Chemistry, Biology, and Marine Science, Chemistry Program, Associate Professor  

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Affiliated academic organizations 【 display / non-display 】

  • 2000.04
    -
    Now
     

    The Geochemical Society of Japan 

  • 2001.04
    -
    Now
     

    The Geological Society of Japan 

  • 2002.04
    -
    Now
     

    American Geophysical Union 

  • 2015.06
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    Now
     

    The Soceity of Sea Water Science, Japan 

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Research Interests 【 display / non-display 】

  • Geochemistry

  • Geochemistry

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Research Areas 【 display / non-display 】

  • Earth Astrochemistry

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Published Papers 【 display / non-display 】

  • Importance of pumiceous sediment in influencing chemistry of hydrothermal fluids in Okinawa Trough: insights from boron isotopic ratios

    Tomohiro Toki, Naoya Ebina, Yuki Mitsutome, Ke-Han Song, Ryuichi Shinjo, Junichiro Ishibashi, Shinsuke Kawagucci

    Progress in Earth and Planetary Science ( Springer Nature )  12 ( 1 ) 115   2025.12 [ 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に対する堆積物の関与について，これまでにも数多くの研究がなされてきている。しかし，その定量的な議論については，いまだに極めて限定的である。そこで，本研究では南部沖縄トラフ及び中部沖縄トラフから複数の海底熱水を採取し，ホウ素濃度及び同位体比を明らかにした。合わせて，周辺堆積物も採取し，それらのホウ素濃度及び同位体比も明らかにした。その結果，熱水中のホウ素濃度は，世界最高の値を示し，一方，ホウ素同位体比は，世界最低の値を示した。さらに，複数の熱水系から得られた熱水のホウ素濃度及び同位体比は，極めて大きな多様性を示し，多様な固相と反応していることが示唆された。一方，堆積物中のホウ素については，軽石以外の値は世界中で報告されているケイ酸塩堆積物の値と一致したが，一方，軽石については沖縄トラフの火山岩と同等の値を示した。中でも，伊平屋北海丘における熱水中のホウ素濃度及び同位体比は，軽石の影響なしには説明できないことが示され，一方，鳩間海丘の熱水中のホウ素については，火山岩と海水との反応だけで説明することが可能であった。一方，第四与那国海丘の海底熱水中のホウ素については，火山岩あるいは堆積物のいずれかと海水との反応だけでは説明が難しく，火山岩及び堆積物のいずれとも反応している必要があることが明らかとなった。伊是名海穴JADEサイトのホウ素については，複数のエンドメンバーがあることが明らかとなり，このことは噴出孔周辺の固相の不均一性を示している可能性がある。

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      DOI Open Access

  • An improved narrower-diameter EA/IRMS method with a built-in desulfurization reactor: optimization for nitrogen and carbon measurement without sulfur matrix interference

    Matsui, Y; Fujisaki, W; Aze, T; Miyajima, T; Kawagucci, S; Tasumi, E; Yamamoto, M; Takano, Y; Toki, T

    PROGRESS IN EARTH AND PLANETARY SCIENCE ( Progress in Earth and Planetary Science )  12 ( 1 )   2025.12 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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      DOI Open Access

  • Estimation of bubbled oxygen flux from a coral reef community

    Tomohiro Toki, Rie Matayoshi, Masataka Yamauchi, Seiichi Koizumi, Hiroyuki Fujimura

    Galaxea, Journal of Coral Reef Studies ( 日本サンゴ礁学会 )  27 ( 1 ) 47 - 61   2025.07 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

    　View Summary

    We collected bubbles from the seafloor of coral reef areas to determine their quantity and chemical composition. The chemical composition was high in oxygen and low in carbon dioxide compared to that of the atmosphere. Oxygen fluxes to the atmosphere from coral reef waters are generally determined considering only dissolved oxygen in seawater, but accounting for bubbled oxygen increased such fluxes by about 70%. At the same time, the primary production rate in coral reefs is estimated only from the dissolved oxygen concentration in seawater, but accounting for bubbled oxygen increased it by about 20–30%. The composition of bubbled gases suggests that approximately 20% of the oxygen present may be derived from photosynthesis in the reef area. Global quantitative estimation of bubbled oxygen fluxes in tropical and subtropical coral reef waters remains critical for future research.

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  • Concentrations and isotope ratios of Mo and W in Okinawa Trough hydrothermal fluids: Novel probes for hydrothermal processes in a back-arc basin

    Kohei Matsuoka, Takano Shotaro, Kawagucci Shinsuke, Toki Tomohiro, Sohrin Yoshiki

    ＧＥＯＣＨＥＭＩＣＡＬ　ＪＯＵＲＮＡＬ ( 一般社団法人日本地球化学会 )  advpub ( 0 )   2025 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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    <p>The concentrations and isotope ratios of molybdenum (Mo) and tungsten (W) are expected to serve as proxies for paleoceanography. Although submarine hydrothermal activities are potentially major sources and sinks of Mo and W, data on these elements in hydrothermal fluids are scarce. In this study, we present the concentrations and isotope ratios of dissolved Mo and W in hydrothermal fluid samples collected from nine active sites—Higashi Ensei, Iheya North, JADE, Hakurei, Higashi Izena, Daisan Kume, Yokosuka, Futagoyama, and Hatoma Knoll—within the Okinawa Trough, which is a back-arc basin. The Mo concentrations ranged from 4.2–411 nmol/kg, <i>δ</i><sup>98/95</sup>Mo values ranged from –0.17 to 3.92‰, W concentrations ranged from 1.7–238 nmol/kg, and <i>δ</i><sup>186/184</sup>W values ranged from –0.03 to 1.08‰. We found that both <i>δ</i><sup>98/95</sup> Mo and <i>δ</i><sup>186/184</sup>W were close to 0‰ when Mo and W were dissolved from rocks and sediments during hydrothermal circulation. The phase separation of the hydrothermal fluids concentrates Mo and W in the liquid phase. Sediments can be a significant source of W at high temperatures and Mo even at low temperatures. The scavenging of Mo by Fe sulfides reduces its concentrations and elevates <i>δ</i><sup> 98/95</sup>Mo values during the emission of high-temperature hydrothermal fluids, while having an insignificant effect on W. The scavenging of W by Fe hydroxides reduces its concentrations and elevates <i>δ</i><sup> 186/184</sup>W values during mixing of hydrothermal fluids and seawater, while having an insignificant effect on Mo. Therefore, the data on Mo and W are useful for investigating the processes that occur during hydrothermal circulation.</p>

  • Origin of helium in basement rocks and carbonate veins in Yonaguni Island

    Toki, T; Yasumura, K; Takahata, N; Miyajima, Y; Miyaki, H; Oohashi, K; Otsubo, M

    GEOCHEMICAL JOURNAL ( 一般社団法人日本地球化学会 )  58 ( 6 ) 293 - 303   2024 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

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    <p>Minerals formed in high-temperature environments are distributed along faults on Yonaguni Island. Volcanic activity is thought to be a possible heat source. In this study, samples from the carbonate veins distributed around the basement rocks and faults of Yonaguni Island were melted in vacuum, and the concentrations and isotope ratios of the noble gases in the furnace were investigated. The observed isotope ratios suggest that the noble gases were dominated by crustal helium, with little influence from mantle helium. These results suggest that there was some kind of non-volcanic heat supply at Yonaguni Island (e.g., eruption of non-volcanic hot springs).</p>

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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

    　View Summary

    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

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Other Papers 【 display / non-display 】

  • Chemistry on coral reefs: In memory of Dr. Tamotsu Oomori (1944–2022)

    Fujimura Hiroyuki, Toki Tomohiro

    Galaxea, Journal of Coral Reef Studies ( 日本サンゴ礁学会 )  27 ( 1 ) 30 - 32   2025.07

     

    DOI CiNii Research Open Access

  • 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

     

  • 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

     

  • Geochemical and geological investigations in the area around the southern Ryukyu islands - Report on RN10 cruise by T/S Nagasaki-maru -

    Tomohiro Toki, Masahide Furukawa, Hiroshi Yoshimura, Youji Kanda, Dae-Yul Baek, Kazuhiko Fujita, and Hiroyuki Fujimura

    Bulletin of the Faculty of Science, University of the Ryukyus ( Faculty of Science, University of the Ryukyus )  ( 91 ) 9 - 19   2011.03

     

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Presentations 【 display / non-display 】

  • Lithium and Strontium Isotope Systematics of Offshore Pore Waters and Onshore Hot Springs from the Noto Peninsula: Geochemical Constraints on Subsurface Fluid Sources Following the 2024 M7.6 Earthquake

    Zahra Zandvakili, Yoshiro Nishio, Tomohiro Toki, Takanori Kagoshima, Jin-Oh Park

    一般社団法人 日本地球化学会 第73回年会(2026)  (京都大学 吉田キャンパス)  2026.09  -  2026.09 

  • Origin of helium in surface sediments in the continental slope area of the East China Sea

    Gen Takatori, Akira Ijiri, Yudai Kobayashi, Takuya Sagawa, Tomohiro Toki, Jun-ichiro Ishibashi, Takanori Kagoshima, Shinpei Otsuka, Jing Zhang, Yoshiro Nishio, Zandvakili Zahra, Jin-Oh Park

    The 133rd Annual Meeting of the Geological Society of Japan (2026Kanazawa)  (Kanazawa University)  2026.09  -  2026.09 

  • Do cold seeps really form at the leading edge during seamount subduction?

    TOKI, Tomohiro

    Can seamount subduction weaken locking of megathrust earthquake  (Earthquake Research Institute, UTokyo; seminar room (Building #1, 2nd floor))  2026.09  -  2026.09 

  • Effect of seamount subduction on seismic couping: Constraint from morphology and heat flow in Hyuga-nada, western Nankai Trough

    Masataka Kinoshita, Yoshitaka Hashimoto, Yohei Hamada, Tomohiro Toki

    AOGS2026  (Fukuoka, Japan)  2026.08  -  2026.08 

  • Concentrations and isotope ratios of Mo and Win Okinawa Trough hydrothermal fluids:Novel probes for hydrothermal processes ina back-arc basin

    Matsuoka Kohei, Yoshiki Sohrin, Shinsuke Kawagucci, Tomohiro Toki and Shotaro Takano

    Goldschmidt 2026  (Montréal, Québec)  2026.07  -  2026.07 

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

  • Can seamount subduction weaken locking of megathrust earthquake? Test at 2 seamounts in Nankai Trough

    Grant-in-Aid for Scientific Research(S)

    Project Year: 2024.04  -  2029.03 

    Direct: 152,900,000 (YEN)  Overheads: 198,770,000 (YEN)  Total: 45,870,000 (YEN)

  • Geosphere-hydrosphere-biosphere connected by submarine mud volcanism: Diffusion processes of deep life and carbon, and their effects on the ocean

    Grant-in-Aid for Scientific Research(A)

    Project Year: 2024.04  -  2029.03 

    Direct: 36,800,000 (YEN)  Overheads: 47,840,000 (YEN)  Total: 11,040,000 (YEN)

  • Geosphere-hydrosphere-biosphere connected by submarine mud volcanism: Diffusion processes of deep life and carbon, and their effects on the ocean

    Grant-in-Aid for Scientific Research(A)

    Project Year: 2024.04  -  2029.03 

    Direct: 36,800,000 (YEN)  Overheads: 47,840,000 (YEN)  Total: 11,040,000 (YEN)

  • Can seamount subduction weaken locking of megathrust earthquake? Test at 2 seamounts in Nankai Trough

    Grant-in-Aid for Scientific Research(S)

    Project Year: 2024.04  -  2029.03 

    Direct: 152,900,000 (YEN)  Overheads: 198,770,000 (YEN)  Total: 45,870,000 (YEN)

  • 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)

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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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SDGs 【 display / non-display 】

  • 与那国島の湧水への海水侵入の進行について

  • 南の島における水資源の有効活用に関する教材

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Amount of external funds acquired by year 【 display / non-display 】

  • 2022year   基盤A，東京地学協会，FOST   3500000yen

  • 2012year   新学術領域   3000000yen

  • 2015year   萌芽   1900000yen

  • 2016year   地域志向推進経費，萌芽   2046755yen

  • 2017year   萌芽   525879yen

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Social Activity 【 display / non-display 】

  • 2026.03
    　
    　

  • 2026.03
    　
    　

  • 2026.02
    　
    　

  • 2026.02
    　
    　

  • 2025.12
    　
    　

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Media Coverage 【 display / non-display 】

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Academic Activities 【 display / non-display 】

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