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Published Papers 【 display / non-display 】

Published Papers 【 display / non-display 】

• 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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• 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)

  　View Summary

  <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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• 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)

  　View Summary

  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)

  　View Summary

  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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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

  　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

Other Papers 【 display / non-display 】

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

   

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• 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 】

Presentations 【 display / non-display 】

• Structural characteristics of the Upper Prism in the Japan Trench suggested by physical and magnetic properties

  Nana Kamiya, Yohei Hamada, Hanaya Okuda, Keisuke Nakamoto, Taizo Uchida, Hinako Hosono, Yoshitaka Hashimoto, Tomohiro Toki, Yusuke Kubo

  AGU Fall Meeting 2025  (New Orleans, LA & Online Everywhere)  2025.12  -  2025.12 

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

  Tomohiro Toki, Ryusei Yonamine, Takanori Kagoshima, Naoto Takahata

  Annual Meeting of the Geological Society of Japan  2025.09  -  2025.09 

• Indigenous traditions and water governance: The case of the Erfeng irrigation canal

  Miyuki Shimabukuro, Tomohiro Toki, Yoshiaki Kubo, Hitoshi Shimabukuro

  The 2nd International Sociohydrology Conference  (東京大学・本郷キャンパス)  2025.07  -  2025.07 

• Origin of lithium in pore fluids near offshore fault zone, northern Noto Peninsula, two months after the 2024 Noto Peninsula earthquake (M7.6) during the R/V Hakuho-maru cruise

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

  日本地球惑星科学連合2025年大会  (幕張メッセ)  2025.05  -  2025.05 

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

  TOKI, Tomohiro

  Annual Meeting of the Geological Society of Japan  2024.09  -  2024.09 

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

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)

• 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)

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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

SDGs 【 display / non-display 】

SDGs 【 display / non-display 】

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

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

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Social Activity 【 display / non-display 】

Social Activity 【 display / non-display 】

• 2025.03

  　

  　

  

• 2024.12

  　

  　

  

• 2024.12

  　

  　

  

• 2024.08

  　

  　

  

• 2024.07

  　

  　

  

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Media Coverage 【 display / non-display 】

Media Coverage 【 display / non-display 】

• 竹富島の地層サンプルを琉大准教授へ寄贈/温泉掘削調査で採取  TV or radio program

  琉球朝日放送・報道制作局  CATCHY  2025.4

  Author： Other 

  　View Summary

  竹富島温泉の掘削試料を，研究に役立ててほしい，というご意思を受け，私が受け取った件に関する記者会見の様子。

• 周辺に海底温泉があるとされる竹富島　地元企業が1000メートル分の地質サンプルを研究者に寄贈  Internet

  RBC  2025.4

  Author： Other 

  　View Summary

  竹富島温泉の掘削試料を，研究に役立ててほしい，というご意思を受け，私が受け取った件に関する記者会見の様子。

• 地下千㍍分の地層試料が琉大に　掘削工事の土質標本寄贈　竹富島黒潮観光  Newspaper, magazine

  八重山毎日新聞  八重山毎日新聞  2025.4

  Author： Other 

  　View Summary

  竹富島温泉の掘削試料を，研究に役立ててほしい，というご意思を受け，私が受け取った件に関する記者会見の様子。

• 「流体」の謎…海底の泥を分析  TV or radio program

  ㈱テレビ朝日  サンデーステーション  2024.3

  Author： Other 

  　View Summary

  能登半島地震では，地球深部から供給されている”流体”が地震を引き起こしていることが指摘されてきているものの，その正体はよくわかっていない。当研究室では，能登半島地震の震源域近くの海底堆積物中から間隙水を抽出して持ち帰り，陸上において化学分析を行うことで，流体の化学組成を明らかにすることを目指している。

• 種子島沖海底泥火山における表層堆積物中の希ガスを用いた流体の起源深度の推定  Internet

  Chem-Station  Chem-Station  2023.5

  Author： Other 

  　View Summary

  種子島沖海底泥火山の表層堆積物中から抽出したガス中の希ガス濃度から，溶解平衡温度を見積もり，その深度を推定したところ，海底下数kmであることが明らかとなった。このことから，本泥火山の表層堆積物中の希ガスが，採取される直前まで海底下数kmにあったことが示唆され，泥火山の噴出現象によって海底直下まで移動させられたことが示唆された。

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Academic Activities 【 display / non-display 】

Academic Activities 【 display / non-display 】

• [International contribution]

  日本地球化学会  （ 琉球大学・千原キャンパス ）

  2018.9

  　

  　

  種別： Academic society, research group, etc. 

  　View Summary

  口頭発表及びポスター発表，夜間集会，学会賞記念講演，総会，懇親会など。関連イベントとして，9月9日（日）に市民講演会，9月10日（月）にショートコース，9月14日（金）にエクスカーションを開催した。

• フジテレビ  （ 奇跡体験！アンビリーバボー ）

  2025.4

  　

  　

  種別： Scientific advice/Review 

  　View Summary

  インドネシアで，村ごと沈んだ泥の噴出現象について，アニメーションで解説したいというディレクターの相談に乗り，イメージを伝え，ナレーション原稿の添削を行った。