Research activity information

• 2017 PNAS, Cozzareli Prize 2017, Applied Biological, Agricaltual, and Environmental Sciences “Methyl-compound use and slow growth characterize microbial life in 2-km-deep subseafloor coal and shale beds”

  Trembath-Reichert, E, Morono, Y, Ijiri, A, Hoshino, T, Dawson, K.S, Inagaki, F, Orphan


• May 2007 Paleo-3 Most Cited Paper 2003-2007 Award, Paleoenvironmental changes in the northern area of the East China Sea during the past 42,00 years

  Ijiri, A, Wang, L, Oba, T, Kawahata, H, Huang, C-Y, Huang , C-Y


• Jul. 2005 日本古生物学会論文賞, 北海道中川地域の白亜系蝦夷層群に見つかった異例に保存の良い湧水性化石群集

  疋田吉識, 鈴木清一, 都郷義寛, 井尻暁

• First direct evidence of the O–H isotopic composition of slab-derived water in the subduction zone, revealed by fluid inclusions in high-pressure metamorphic rocks

  Kenta K. Yoshida, Ryu Uemura, Akira Ijiri, Minoru Ikehara, Takao Hirajima

  Abstract The O and H isotopic compositions of water provide clues to their origin and the water cycle in the deep Earth, and those of waters from hot springs can indicate their deep, non-meteoric origin. Quartz veins in high-pressure type metamorphic rocks can provide crucial information on paleo-subduction zone fluids. We investigated the O and H isotopic compositions of fluid inclusions in quartz veins collected from the Sanbagawa metamorphic belt, SW Japan, that are thought to preserve a trace element signature from slab-derived water. A total of 300–1000 mg of purified quartz grains were crushed, and the O and H isotopic compositions of the extracted water were analyzed using cavity ring-down spectroscopy (CRDS). The O isotopic compositions of the residual host quartz were determined by continuous-flow isotope ratio mass spectrometry (CF-IRMS). The fluid inclusions in schistosity-parallel quartz veins, which yield the trace element signatures of slab-derived water, have O and H isotopic compositions that do not plot along the meteoric water line but are consistent with previous numerical models of slab-derived water. Furthermore, the depths of the slab-derived water predicted by the numerical models are consistent with the peak pressures of the host metamorphic rocks. In contrast, fluid inclusions in quartz veins that cut across the main schistosity in the host rocks, which likely formed during the exhumation of the rock, have an isotopic composition intermediate between those of meteoric and slab-derived waters. The estimated temperature of equilibrium between the water and quartz O isotopic compositions is not consistent with the peak metamorphic temperature of the host rock, suggesting disequilibrium between the bulk quartz vein and trapped fluids. These results are the first direct evidence of the stable isotopic composition of slab-derived water, and thereby highlight the importance of direct determination of paleo-fluid composition using fluid inclusions.

  Springer Science and Business Media LLC, May 2025, Geoscience Letters, 12(1) (1)

  [Refereed]

  Scientific journal


• Kinetic oxygen isotopic fractionation evaluated by amorphous silica synthesized at 10–40°C

  Haruko Kawaguchi, Masako Hori, Akira Ijiri, Minoru Ikehara

  Geochemical Society of Japan, 2025, GEOCHEMICAL JOURNAL, 59(1) (1), 26 - 34

  [Refereed]

  Scientific journal


• Fossil tubeworms from the Middle Miocene Bessho Formation in Matsumoto City, Nagano Prefecture, Central Japan

  Takami Nobuhara, Hakuichi Koike, Akira Ijiri

  Mar. 2024, Fossils, 115, 53 - 64, Japanese

  [Refereed]


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

  Miho Asada, Mikiya Yamashita, Rina Fukuchi, Toshiyuki Yokota, Tomohiro Toki, Akira Ijiri, Kiichiro Kawamura

  Nov. 2023, Frontiers in Earth Science, 11

  [Refereed]

  Scientific journal


• Cultivation of Piezotolerant and Piezophilic Hyperthermophiles with a Newly Developed Constant High Pressure and Temperature Culturing and Monitoring System

  Mori Fumiaki, Ijiri Akira, Nishimura Tomoya, Wakamatsu Taisuke, Katsuki Nozomi, Morono Yuki

  The Earth’s microbial biosphere extends from ambient to extreme environments, including deep-sea hydrothermal vents and subseafloor habitats. Despite efforts to understand the physiological adaptations of these microbes, our knowledge is limited due to the technological challenges associated with reproducing in situ high temperature (HT)-high hydrostatic pressure (HHP) conditions and sampling HT-HHP cultures. In the present study, we developed a new high temperature and pressure (HTP) incubation system that enabled the maintenance of HT-HHP conditions while sampling incubation medium and mostly eliminated non-biological reactions, including hydrogen generation or the leakage of small gaseous molecules. The main characteristics of our system are (1) a chamber made of gold with gold-etched lid parts that suppress the majority of non-biological reactions, (2) the exceptional containment of dissolved gas, even small molecules, such as hydrogen, and (3) the sampling capacity of intra-chamber liquid without depressurization and the isobaric transfer of a culture to inoculate new medium. We initially confirmed the retention of dissolved hydrogen in the incubation container at 82°C and 20‍ ‍MPa for 9 days. Cultivation tests with an obligate hyperthermophilic piezophile (Pyrococcus yayanosii), hydrogenotrophic hyperthermophile (Archaeoglobus profundus), and heterotrophic hyperthermophile (Pyrococcus horikoshii) were successful based on growth monitoring and chemical ana­lyses. During HTP cultivation, we observed a difference in the duration of the lag phase of P. horikoshii, which indicated the potential effect of a pressure change on the physiology of piezophiles. The present results suggest the importance of a cultivation system designed and developed explicitly for HTP conditions with the capacity for sampling without depressurization of the entire system.

  Japanese Society of Microbial Ecology / Japanese Society of Soil Microbiology / Taiwan Society of Microbial Ecology / Japanese Society of Plant Microbe Interactions / Japanese Society for Extremophiles, Oct. 2023, Microbes and Environments, 38(6) (6), n/a, English

  [Refereed]


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

  Yuki Mitsutome, Ko Agena, Tomohiro Toki, Ke-Han Song, Ryuichi Shinjo, Akira Ijiri

  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.

  Frontiers Media SA, Sep. 2023, Frontiers in Marine Science, 10

  [Refereed]

  Scientific journal


• 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

  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.

  Frontiers Media SA, Jul. 2023, Frontiers in Earth Science, 11, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Estimation of the depth of origin of fluids using noble gases in the surface sediments of submarine mud volcanoes off Tanegashima Island.

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

  The helium isotope ratio (3He/4He), concentration ratio of neon-20 to helium-4 (20Ne/4He), argon (Ar), krypton (Kr), and xenon (Xe) concentrations were measured in the porewater of surface sediments of several submarine mud volcanoes. From the 3He/4He values (0.18-0.93RA), the estimated He origin is almost 90% crustal He, with little contribution from mantle-derived He. The determined Ar, Kr, and Xe concentrations lie within the solubility equilibrium range expected for temperatures from 83 °C up to 230 °C and are consistent with the temperature range of the dehydration origin of clay minerals. Considering the geothermal gradient in the investigated region (25 °C/km), these gases are considered to have reached dissolution equilibrium at a depth of about 3.3 km to 9.2 km below the seafloor. As the depth of the plate boundary is 18 km below the seafloor, the noble gas signatures are likely to originate from the crust, not from the plate boundary. This is consistent with the results presented by the He isotope ratios.

  Apr. 2023, Scientific reports, 13(1) (1), 5051 - 5051, English, International magazine

  [Refereed]

  Scientific journal


• A simple method for taxon-specific purification of diatom frustules from ocean sediments using a cell sorter

  Yuji Kato, Yuki Morono, Akira Ijiri, Takeshi Terada, Minoru Ikehara

  Abstract It is necessary to purify diatom frustules by taxon to perform accurate geochemical analyses of diatom fossils preserved in sediments. However, the small size of diatoms has hitherto prevented taxon-specific purification; therefore, previous geochemical analyses of diatom frustules have been performed with mixtures of various taxa. In this study, we developed a taxon-selective collection method of diatom fossils that uses a cell sorter. The experimental material comprised six samples from a sediment core of Hole U1538A in the Scotia Sea, Atlantic sector of the Southern Ocean drilled during the International Ocean Discovery Program Expedition 382. Following conventional pretreatments (removal of organic matter and carbonates as well as clay minerals), we conducted cell sorter experiments focusing on the optical and fluorescence characteristics of the diatom fossils. We succeeded in selectively isolating with high purity five diatom taxa representing the Southern Ocean diatom flora: (1) discoid diatoms (mainly Thalassiosira) with a moderate degree of fluorescence; (2) Fragilariopsis (mainly Fragilariopsis kerguelensis), which exhibits the highest fluorescence values; (3) Rhizosolenia; (4) Eucampia antarctica; and (5) needle-shaped diatoms (Thalassiothrix). This taxon-specific diatom purification method will enable more accurate geochemical analyses, such as the oxygen isotope ratio (δ¹⁸O) of diatom frustules, which is likely to lead to significant advances in paleoceanography, especially at high latitudes or in upwelling zones where diatoms are abundant. This method will also be useful in paleolimnology, ocean biology, and phycology.

  Springer Science and Business Media LLC, Mar. 2023, Progress in Earth and Planetary Science, 10(1) (1)

  [Refereed]

  Scientific journal


• Unique H2-utilizing lithotrophy in serpentinite-hosted systems.

  Masaru Konishi Nobu, Ryosuke Nakai, Satoshi Tamazawa, Hiroshi Mori, Atsushi Toyoda, Akira Ijiri, Shino Suzuki, Ken Kurokawa, Yoichi Kamagata, Hideyuki Tamaki

  Serpentinization of ultramafic rocks provides molecular hydrogen (H2) that can support lithotrophic metabolism of microorganisms, but also poses extremely challenging conditions, including hyperalkalinity and limited electron acceptor availability. Investigation of two serpentinization-active systems reveals that conventional H2-/CO2-dependent homoacetogenesis is thermodynamically unfavorable in situ due to picomolar CO2 levels. Through metagenomics and thermodynamics, we discover unique taxa capable of metabolism adapted to the habitat. This included a novel deep-branching phylum, "Ca. Lithacetigenota", that exclusively inhabits serpentinite-hosted systems and harbors genes encoding alternative modes of H2-utilizing lithotrophy. Rather than CO2, these putative metabolisms utilize reduced carbon compounds detected in situ presumably serpentinization-derived: formate and glycine. The former employs a partial homoacetogenesis pathway and the latter a distinct pathway mediated by a rare selenoprotein-the glycine reductase. A survey of microbiomes shows that glycine reductases are diverse and nearly ubiquitous in serpentinite-hosted environments. "Ca. Lithacetigenota" glycine reductases represent a basal lineage, suggesting that catabolic glycine reduction is an ancient bacterial innovation by Terrabacteria for gaining energy from geogenic H2 even under hyperalkaline, CO2-poor conditions. Unique non-CO2-reducing metabolisms presented here shed light on potential strategies that extremophiles may employ for overcoming a crucial obstacle in serpentinization-associated environments, features potentially relevant to primordial lithotrophy in early Earth.

  Jan. 2023, The ISME journal, 17(1) (1), 95 - 104, English, International magazine

  [Refereed]

  Scientific journal


• Origin, migration and alteration of gases from surface seeps and mud volcanoes in the Niigata basin

  Amane Waseda, Fumiaki Okumura, Akira Ijiri, Hirotsugu Iwano

  Nov. 2022, Journal of the Japanese Association for Petroleum Technology, 87(6) (6), 454 - 462, Japanese

  [Refereed]

  Scientific journal


• Spring discharge mechanism along the southeast coast of Yonaguni Island in the southern Ryukyu forearc

  Tomohiro Toki, Hina Kataoka, Ryogo Takada, Shinji Nakaya, Syogo Oshima, Akira Ijiri

  Apr. 2022, JOURNAL OF HYDROLOGY-REGIONAL STUDIES, 40, English

  [Refereed]

  Scientific journal


• Purification of Disc-Shaped Diatoms from the Southern Ocean Sediment by a Cell Sorter to Obtain an Accurate Oxygen Isotope Record

  Akira Ijiri, Takeshi Izumi, Yuki Morono, Yuji Kato, Takeshi Terada, Minoru Ikehara

  Oct. 2021, ACS EARTH AND SPACE CHEMISTRY, 5(10) (10), 2792 - 2806, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• A Seafloor Survey Using Multiple Methodologies to Verify the Existence of a Village Submerged after a Historical Nankai Earthquake in Nomi Bay, Kochi Prefecture

  TANIKAWA Wataru, OKAZAKI Keishi, TOKUYAMA Hidekazu, MURAYAMA Masafumi, IJIRI Akira, HIROSE Takehiro, URAMOTO Go-ichiro, HOSHINO Tatsuhiko, TANAKA Kouki, YAMAMOTO Yuhji, HAMADA Yohei

  Coastal Oceanography Research Committee, the Oceanographic Society of Japan, 2021, Bulletin on Coastal Oceanography, 2021, Japanese

  [Refereed]


• Temperature limits to deep subseafloor life in the Nankai Trough subduction zone.

  Verena B Heuer, Fumio Inagaki, Yuki Morono, Yusuke Kubo, Arthur J Spivack, Bernhard Viehweger, Tina Treude, Felix Beulig, Florence Schubotz, Satoshi Tonai, Stephen A Bowden, Margaret Cramm, Susann Henkel, Takehiro Hirose, Kira Homola, Tatsuhiko Hoshino, Akira Ijiri, Hiroyuki Imachi, Nana Kamiya, Masanori Kaneko, Lorenzo Lagostina, Hayley Manners, Harry-Luke McClelland, Kyle Metcalfe, Natsumi Okutsu, Donald Pan, Maija J Raudsepp, Justine Sauvage, Man-Yin Tsang, David T Wang, Emily Whitaker, Yuzuru Yamamoto, Kiho Yang, Lena Maeda, Rishi R Adhikari, Clemens Glombitza, Yohei Hamada, Jens Kallmeyer, Jenny Wendt, Lars Wörmer, Yasuhiro Yamada, Masataka Kinoshita, Kai-Uwe Hinrichs

  Microorganisms in marine subsurface sediments substantially contribute to global biomass. Sediments warmer than 40°C account for roughly half the marine sediment volume, but the processes mediated by microbial populations in these hard-to-access environments are poorly understood. We investigated microbial life in up to 1.2-kilometer-deep and up to 120°C hot sediments in the Nankai Trough subduction zone. Above 45°C, concentrations of vegetative cells drop two orders of magnitude and endospores become more than 6000 times more abundant than vegetative cells. Methane is biologically produced and oxidized until sediments reach 80° to 85°C. In 100° to 120°C sediments, isotopic evidence and increased cell concentrations demonstrate the activity of acetate-degrading hyperthermophiles. Above 45°C, populated zones alternate with zones up to 192 meters thick where microbes were undetectable.

  Dec. 2020, Science (New York, N.Y.), 370(6521) (6521), 1230 - 1234, English, International magazine

  [Refereed]

  Scientific journal


• New Chikyu Shallow Core Program (SCORE): exploring mass transport deposits and the subseafloor biosphere off Cape Erimo, northern Japan

  Yusuke Kubo, Fumio Inagaki, Satoshi Tonai, Go-Ichiro Uramoto, Osamu Takano, Yasuhiro Yamada, the Expedition, Shipboard Scientific Party

  Copernicus GmbH, May 2020, Scientific Drilling, 27, 25 - 33, English

  [Refereed]

  Scientific journal


• Hot fluids, burial metamorphism and thermal histories in the underthrust sediments at IODP 370 site C0023, Nankai Accretionary Complex

  Man Yin Tsang, Stephen A. Bowden, Zhibin Wang, Abdalla Mohammed, Satoshi Tonai, David Muirhead, Kiho Yang, Yuzuru Yamamoto, Nana Kamiya, Natsumi Okutsu, Takehiro Hirose, Myriam Kars, Florence Schubotz, Akira Ijiri, Yasuhiro Yamada, Yusuke Kubo, Yuki Morono, Fumio Inagaki, Verena B. Heuer, Kai Uwe Hinrichs

  Feb. 2020, Marine and Petroleum Geology, 112

  [Refereed]

  Scientific journal


• Significance of biogeochemical processes in mud volcanoes

  井尻 暁

  日本地質学会, Jan. 2020, 地質学雑誌, 126(1) (1), 29 - 37, Japanese

  [Refereed]


• Constraints on the fluid supply rate into and through gas hydrate reservoir systems as inferred from pore-water chloride and in situ temperature profiles, Krishna-Godavari Basin, India

  Masataka Kinoshita, Akira Ijiri, Satoru Haraguchi, Francisco Jose Jiménez-Espejo, Nobuharu Komai, Hisami Suga, Takamitsu Sugihara, Wataru Tanikawa, Takehiro Hirose, Yohei Hamada, Lallan P. Gupta, Naokazu Ahagon, Yuka Masaki, Natsue Abe, Hung Y. Wu, Shun Nomura, Weiren Lin, Yuzuru Yamamoto, Yasuhiro Yamada

  Elsevier BV, Oct. 2019, Marine and Petroleum Geology, 108, 368 - 376, English

  [Refereed]

  Scientific journal


• A New Method for Quality Control of Geological Cores by X-Ray Computed Tomography: Application in IODP Expedition 370

  Satoshi Tonai, Yusuke Kubo, Man-Yin Tsang, Stephen Bowden, Kotaro Ide, Takehiro Hirose, Nana Kamiya, Yuzuru Yamamoto, Kiho Yang, Yasuhiro Yamada, Yuki Morono, Verena B. Heuer, Fumio Inagaki, Lena Maeda, Margaret Cramm, Susann Henkel, Kira Homola, Tatsuhiko Hoshino, Akira Ijiri, Hiroyuki Imachi, Masanori Kaneko, Lorenzo Lagostina, Hayley Manners, Ilarry-Luke McClelland, Kyle Metcalfe, Natsumi Okutsu, Donald Pan, Maija Jocelyn Raudsepp, Justine Sauvage, Florence Schubotz, Arthur Spivack, Tina Treude, Bernhard Viehweger, David T. Wang, Emily Whitaker, Masataka Kinoshita

  May 2019, FRONTIERS IN EARTH SCIENCE, 7, English

  [Refereed]

  Scientific journal


• Cultivable microbial community in 2-km-deep, 20-million-year-old subseafloor coalbeds through ~1000 days anaerobic bioreactor cultivation.

  Hiroyuki Imachi, Eiji Tasumi, Yoshihiro Takaki, Tatsuhiko Hoshino, Florence Schubotz, Shuchai Gan, Tzu-Hsuan Tu, Yumi Saito, Yuko Yamanaka, Akira Ijiri, Yohei Matsui, Masayuki Miyazaki, Yuki Morono, Ken Takai, Kai-Uwe Hinrichs, Fumio Inagaki

  Feb. 2019, Scientific reports, 9(1) (1), 2305 - 2305, English, International magazine

  [Refereed]


• Indian Monsoonal Variations During the Past 80 Kyr Recorded in NGHP-02 Hole 19B, Western Bay of Bengal: Implications From Chemical and Mineral Properties

  Yuki Ota, Hodaka Kawahata, Junichiro Kuroda, Asuka Yamaguchi, Atsushi Suzuki, Daisuke Araoka, Ayako Abe-Ouchi, Yasuhiro Yamada, Akira Ijiri, Toshiya Kanamatsu, Masataka Kinoshita, Kyaw Thu Moe, Weiren Lin, Saneatsu Saito, Yoshinori Sanada, Yohei Hamada, Yasuyuki Nakamura, Yuichi Shinmoto, Hung Yu Wu, Naokazu Ahagon, Kan Aoike, Koichi Iijima, Hideaki Machiyama, Maria Luisa Tejada, Keita Umetsu, Yoichi Usui, Yuzuru Yamamoto, Shuro Yoshikawa, Francisco Jimenez-Espejo, Satoru Haraguchi, Nobuharu Komai, Hisami Suga, Natsue Abe, Lallan Gupta, Takehiro Hirose, Yuka Masaki, Shun Nomura, Takamitsu Sugihara, Wataru Tanikawa, Yusuke Kubo, Lena Maeda, Sean Toczko

  Jan. 2019, GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 20(1) (1), 148 - 165, English

  [Refereed]

  Scientific journal


• Microbial Metabolism and Community Dynamics in Hydraulic Fracturing Fluids Recovered From Deep Hydrocarbon-Rich Shale.

  Yuki Morono, Jessie R Wishart, Motoo Ito, Akira Ijiri, Tatsuhiko Hoshino, Marta Torres, Circe Verba, Takeshi Terada, Fumio Inagaki, Frederick S Colwell

  2019, Frontiers in microbiology, 10, 376 - 376, English, International magazine

  [Refereed]

  Scientific journal


• In-situ mechanical weakness of subducting sediments beneath a plate boundary décollement in the Nankai Trough

  Yohei Hamada, Takehiro Hirose, Akira Ijiri, Yasuhiro Yamada, Yoshinori Sanada, Saneatsu Saito, Noriaki Sakurai, Takamitsu Sugihara, Takahiro Yokoyama, Tomokazu Saruhashi, Tatsuhiko Hoshino, Nana Kamiya, Stephen Bowden, Margaret Cramm, Susann Henkel, Kira Homola, Hiroyuki Imachi, Masanori Kaneko, Lorenzo Lagostina, Hayley Manners, Harry-Luke McClelland, Kyle Metcalfe, Natsumi Okutsu, Donald Pan, Maija Jocelyn Raudsepp, Justine Sauvage, Florence Schubotz, Arthur Spivack, Satoshi Tonai, Tina Treude, Man-Yin Tsang, Bernhard Viehweger, David T. Wang, Emily Whitaker, Yuzuru Yamamoto, Kiho Yang, Masataka Kinoshita, Lena Maeda, Yusuke Kubo, Yuki Morono, Fumio Inagaki, Verena B. Heuer

  Dec. 2018, Progress in Earth and Planetary Science, 5(1) (1)

  [Refereed]

  Scientific journal


• Origin of methane and heavier hydrocarbons entrapped within Miocene methane-seep carbonates from central Japan

  Miyajima Yusuke, Ijiri Akira, Miyake Akira, Hasegawa Takashi

  Oct. 2018, CHEMICAL GEOLOGY, 498, 83 - 95

  [Refereed]


• Deep-biosphere methane production stimulated by geofluids in the Nankai accretionary complex.

  Akira Ijiri, Fumio Inagaki, Yusuke Kubo, Rishi R Adhikari, Shohei Hattori, Tatsuhiko Hoshino, Hiroyuki Imachi, Shinsuke Kawagucci, Yuki Morono, Yoko Ohtomo, Shuhei Ono, Sanae Sakai, Ken Takai, Tomohiro Toki, David T Wang, Marcos Y Yoshinaga, Gail L Arnold, Juichiro Ashi, David H Case, Tomas Feseker, Kai-Uwe Hinrichs, Yojiro Ikegawa, Minoru Ikehara, Jens Kallmeyer, Hidenori Kumagai, Mark A Lever, Sumito Morita, Ko-Ichi Nakamura, Yuki Nakamura, Manabu Nishizawa, Victoria J Orphan, Hans Røy, Frauke Schmidt, Atsushi Tani, Wataru Tanikawa, Takeshi Terada, Hitoshi Tomaru, Takeshi Tsuji, Urumu Tsunogai, Yasuhiko T Yamaguchi, Naohiro Yoshida

  Jun. 2018, Science advances, 4(6) (6), eaao4631, English, International magazine

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Clay mineral suites in submarine mud volcanoes in the kumano forearc basin, nankai trough: Constraints on the origin of mud volcano sediments

  Akira Ijiri, Koichi Iijima, Urumu Tsunogai, Juichiro Ashi, Fumio Inagaki

  Jun. 2018, Geosciences (Switzerland), 8(6) (6), English

  [Refereed]

  Scientific journal


• Low-Temperature Clay Mineral Dehydration Contributes to Porewater Dilution in Bering Sea Slope Subseafloor

  Ijiri, Akira, Tomioka, Naotaka, Wakaki, Shigeyuki, Masuda, Harue, Shozugawa, Katsumi, Kim, Sunghan, Khim, Boo-Keun, Murayama, Masafumi, Matsuo, Motoyuki, Inagaki, Fumio

  Apr. 2018, FRONTIERS IN EARTH SCIENCE, 6, English

  [Refereed]

  Scientific journal


• Interactions between biogenic gas and microbial activity in the subseafloor:- Frontiers in scientific ocean drilling

  Inagaki Fumio, Ijiri Akira, Kitada Kazuya, Machiyama Hideaki

  Scientific ocean drilling has a history of about half a century, which has so far brought remarkable discoveries in Earth Science, such as demonstration of plate tectonics and drastic environmental changes that occurred in the past on our planet. Among them, the substantial expansion of our knowledge on the discovery of "deep subseafloor biosphere" is one of the milestone scientific achievements that overturned the paradigm of the habitability in Earthʼs interior. To date, numerous multidisciplinary studies of sediment samples cored from subseafloor have demonstrated that a remarkable number of physiologically and thus functionary unknown microorganisms are predominant, which have indigenously evolved under the dark subsurface biosphere. On-going effort on scientific exploration of the deep biosphere shows that functionality of the deep microbial ecosystem lurking inside of the Earth indeed plays important ecological roles in the global carbon and other elemental cycling; e.g., degradation processes of the buried organic matter, formation processes of biogenic gas including methane hydrates in the global subseafloor sedimentary environments. In this lecture, we introduce the recent scientific knowledge on the interaction between the occurrence of biogenic gas and the deepbiosphere activity, and discuss how we could develop carbon and energy circulation systems for the sustainable human society and Earthʼs environment in the future.

  The Japanese Association for Petroleum Technology, 2018, Journal of the Japanese Association for Petroleum Technology, 83(2) (2), 130 - 137, Japanese

  [Refereed]


• Uptake of porewater phosphate by REY-rich mud in the western North Pacific Ocean

  Akira Ijiri, Kei Okamura, Junichiro Ohta, Yoshiro Nishio, Yohei Hamada, Koichi Iijima, Fumio Inagaki

  2018, GEOCHEMICAL JOURNAL, 52(4) (4), 373 - 378, English

  [Refereed]

  Scientific journal


• Origin of low-chloride fluid in sediments from the eastern continental margin of India, results from the National Gas Hydrate Program Expedition 02

  Akira Ijiri, Satoru Haraguchi, Francisco Jose Jiménez-Espejo, Nobuharu Komai, Hisami Suga, Masataka Kinoshita, Fumio Inagaki, Yasuhiro Yamada, NGHP Expedition 02 JAMSTEC Science Team

  Elsevier Ltd, 2018, Marine and Petroleum Geology, 108, 377 - 388, English

  [Refereed]

  Scientific journal


• Exploration of the deep-subseafloor-biosphere frontiers: Achievements and perspectives

  Inagaki Fumio, Imachi Hiroyuki, Kubo Yusuke, Morono Yuki, Hoshino Tatsuhiko, Ijiri Akira, Xiao Nan, Suzuki Shino, Ishii Shunichi, Uramoto Go-ichiro, Terada Takeshi

  Scientific ocean drilling over the past half-century has significantly expanded our knowledge of life, ocean, and Earth. The discovery of the spatially vast deep-subseafloor biosphere, a milestone scientific achievement, has extended the planetary habitability of life on Earth. To date, multiple lines of evidence form the core samples have demonstrated that a remarkable amount of physiologically unknown microbial life is present deep beneath the ocean floor where water supply and energy substrates are severely limited. Although subseafloor microbial ecosystems generally function extremely slowly, the consequence of long-term activity on geological timescales may play significant ecological roles in global biogeochemical carbon and other elemental cycles.

  The Geological Society of Japan, 2018, The Journal of the Geological Society of Japan, 124(1) (1), 77 - 92, Japanese

  [Refereed]


• Aerobic and Anaerobic Methanotrophic Communities Associated with Methane Hydrates Exposed on the Seafloor: A High-Pressure Sampling and Stable Isotope-Incubation Experiment

  David H. Case, Akira Ijiri, Yuki Morono, Patricia Tavormina, Victoria J. Orphan, Fumio Inagaki

  Dec. 2017, FRONTIERS IN MICROBIOLOGY, 8, English

  [Refereed]

  Scientific journal


• Methyl-compound use and slow growth characterize microbial life in 2-km-deep subseafloor coal and shale beds

  Elizabeth Trembath-Reichert, Yuki Morono, Akira Ijiri, Tatsuhiko Hoshino, Katherine S. Dawson, Fumio lnagaki, Victoria J. Orphan

  Oct. 2017, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 114(44) (44), E9206 - E9215, English

  [Refereed]

  Scientific journal


• Atribacteria from the Subseafloor Sedimentary Biosphere Disperse to the Hydrosphere through Submarine Mud Volcanoes

  Tatsuhiko Hoshino, Tomohiro Toki, Akira Ijiri, Yuki Morono, Hideaki Machiyama, Juichiro Ashi, Kei Okamura, Fumio Inagaki

  Jun. 2017, FRONTIERS IN MICROBIOLOGY, 8, English

  [Refereed]

  Scientific journal


• Defining boundaries for the distribution of microbial communities beneath the sediment-buried, hydrothermally active seafloor

  Katsunori Yanagawa, Akira Ijiri, Anja Breuker, Sanae Sakai, Youko Miyoshi, Shinsuke Kawagucci, Takuroh Noguchi, Miho Hirai, Axel Schippers, Jun-ichiro Ishibashi, Yoshihiro Takaki, Michinari Sunamura, Tetsuro Urabe, Takuro Nunoura, Ken Takai

  Feb. 2017, ISME JOURNAL, 11(2) (2), 529 - 542, English

  [Refereed]

  Scientific journal


• Data report: permeability of~ 1.9 km deep coal-bearing formation samples off the Shimokita Peninsula, Japan

  Akira Ijiri, Yojiro Ikegawa, Fumio Inagaki

  2017, Proc. IODP| Volume, 337, 2, English

  [Refereed]

  Research society


• Mass occurrence of the enigmatic gastropod Elmira in the Late Cretaceous Sada Limestone seep deposit in southwestern Shikoku, Japan

  Takami Nobuhara, Daigaku Onda, Takuya Sato, Hidemi Aosawa, Toyoho Ishimura, Akira Ijiri, Urumu Tsunogai, Naoki Kikuchi, Yasuo Kondo, Steffen Kiel

  Dec. 2016, PALAEONTOLOGISCHE ZEITSCHRIFT, 90(4) (4), 701 - 722, English

  [Refereed]

  Scientific journal


• Limited reduction of ferrihydrite encrusted by goethite in freshwater sediment

  S. Kikuchi, H. Makita, U. Konno, F. Shiraishi, A. Ijiri, K. Takai, M. Maeda, Y. Takahashi

  Jul. 2016, GEOBIOLOGY, 14(4) (4), 374 - 389, English

  [Refereed]

  Scientific journal


• IODP Expedition 337: Deep Coalbed Biosphere off Shimokita - Microbial processes and hydrocarbon system associated with deeply buried coalbed in the ocean

  Fumio Inagaki, Kai Uwe Hinrichs, Yusuke Kubo, Monika Bihan, Stephen A. Bowden, Marshall Bowles, Marcus Elvert, Clemens Glombitza, Doris Gross, Guy J. Harrington, Verena Heuer, Wei Li Hong, Tomoyuki Hori, Tatsuhiko Hoshino, Akira Ijiri, Hiroyuki Imachi, Motoo Ito, Masanori Kaneko, Mark A. Lever, Kevin Li, David Limmer, Yu Shih Lin, Chang Hong Liu, Barbara A. Methé, Sumito Morita, Yuki Morono, Masafumi Murayama, Naohiko Ohkouchi, Shuhei Ono, Young Soo Park, Stephen C. Phillips, Xavier Prieto-Mollar, Marcella Purkey, Natascha Riedinger, Yoshinori Sanada, Justine Sauvage, Glen Snyder, Rita Susilawati, Yoshinori Takano, Wataru Tanikawa, Eiji Tasumi, Takeshi Terada, Hitoshi Tomaru, Elizabeth Trembath-Reichert, David T. Wang, Yasuhiro Yamada

  Jun. 2016, Scientific Drilling, 21, 17 - 28, English

  [Refereed]

  Scientific journal


• Discovery of extremely REY-rich mud in the western North Pacific Ocean

  Koichi Iijima, Kazutaka Yasukawa, Koichiro Fujinaga, Kentaro Nakamura, Shiki Machida, Yutaro Takaya, Junichiro Ohta, Satoru Haraguchi, Yoshiro Nishio, Yoichi Usui, Tatsuo Nozaki, Toshitsugu Yamazaki, Yuji Ichiyama, Akira Ijiri, Fumio Inagaki, Hideaki Machiyama, Katsuhiko Suzuki, Yasuhiro Kato

  2016, GEOCHEMICAL JOURNAL, 50(6) (6), 557 - 573, English

  [Refereed]

  Scientific journal


• Geochemistry of REY-rich mud in the Japanese Exclusive Economic Zone around Minamitorishima Island

  Koichiro Fujinaga, Kazutaka Yasukawa, Kentaro Nakamura, Shiki Machida, Yutaro Takaya, Junichiro Ohta, Shuhei Araki, Hanjie Liu, Ryo Usami, Ryota Maki, Satoru Haraguchi, Yoshiro Nishio, Yoichi Usui, Tatsuo Nozaki, Toshitsugu Yamazaki, Yuji Ichiyama, Akira Ijiri, Fumio Inagaki, Hideaki Machiyama, Koichi Iijima, Katsuhiko Suzuki, Yasuhiro Kato

  2016, GEOCHEMICAL JOURNAL, 50(6) (6), 575 - 590, English

  [Refereed]

  Scientific journal


• Geochemical characteristics of hydrothermal fluids at Hatoma Knoll in the southern Okinawa Trough

  Tomohiro Toki, Michihiro Itoh, Daigo Iwata, Shogo Ohshima, Ryuichi Shinjo, Jun-Ichiro Ishibashi, Urumu Tsunogai, Naoto Takahata, Yuji Sano, Toshiro Yamanaka, Akira Ijiri, Nobuaki Okabe, Toshitaka Gamo, Yasuyuki Muramatsu, Yuichiro Ueno, Shinsuke Kawagucci, Ken Takai

  2016, GEOCHEMICAL JOURNAL, 50(6) (6), 493 - 525, English

  [Refereed]

  Scientific journal


• Experiments on interstitial water squeezing at high pressure using water-gathering plates

  Yu'suke Kubo, Yuya Hitomi, Akira Ijiri

  A sediment squeezing tool for use in interstitial water extraction at the onboard laboratory of D/V Chikyu was modified for use at pressures up to 112.3 MPa. A pair of titanium water-gathering plate originally developed by Central Research Institute of Electric Power Industry (CRIEPI) replaces a thin mesh to allow squeezing of sediment at a higher pressure without jamming of sediments. The modified tool endured a longer period of squeezing at high pressure, and yielded greater volume of interstitial water in test experiments. The acquired fluid sample composition showed no major changes even at the pressure of 112.3 MPa, although further tests must be conducted to assess the potential dehydration of clay mineral at high pressures. However, squeezing of sandstone of approximately 12％ porosity yielded no interstitial water at all, showing system limitations for low-porosity samples. The improved tool and the data from these experiments are expected to be useful when low-porosity sediments from a deep hole are obtained.

  Japan Agency for Marine-Earth Science and Technology, Sep. 2015, JAMSTEC Report of Research and Development, 21, 17 - 22, English

  [Refereed]

  Scientific journal


• Exploring deep microbial life in coal-bearing sediment down to ∼2.5 km below the ocean floor

  F. Inagaki, K. U. Hinrichs, Y. Kubo, M. W. Bowles, V. B. Heuer, W. L. Hong, T. Hoshino, A. Ijiri, H. Imachi, M. Ito, M. Kaneko, M. A. Lever, Y. S. Lin, B. A. Methé, S. Morita, Y. Morono, W. Tanikawa, M. Bihan, S. A. Bowden, M. Elvert, C. Glombitza, D. Gross, G. J. Harrington, T. Hori, K. Li, D. Limmer, C. H. Liu, M. Murayama, N. Ohkouchi, S. Ono, Y. S. Park, S. C. Phillips, X. Prieto-Mollar, M. Purkey, N. Riedinger, Y. Sanada, J. Sauvage, G. Snyder, R. Susilawati, Y. Takano, E. Tasumi, T. Terada, H. Tomaru, E. Trembath-Reichert, D. T. Wang, Y. Yamada

  Jul. 2015, Science, 349(6246) (6246), 420 - 424

  [Refereed]

  Scientific journal


• Origins of lithium in submarine mud volcano fluid in the Nankai accretionary wedge

  Nishio, Yoshiro, Ijiri, Akira, Toki, Tomohiro, Morono, Yuki, Tanimizu, Masaharu, Nagaishi, Kazuya, Inagaki, Fumio

  2015, Earth and Planetary Science Letters, 414, 144 - 155

  [Refereed]

  Scientific journal


• CO₂ emission and shallow-type methane hydrate decomposition experiment on deep-sea floor

  Ohtomo Yoko, Fukuba Tatsuhiro, Nagasawa Makoto, Matsumoto Masamitsu, Inagaki Fumio, Ijiri Akira, Morono Yuki, Ikegawa Yojiro, Suenaga Hiroshi, Case David, Machiyama Hideaki, Yamamoto Fujio, Goto Shusaku

  Increasing anthropogenic CO₂ in the atmosphere causes global warming and subsequent environmental changes, which may lead to an increase in natural disasters jeopardizing human society. Prompt technological development for CO₂ capture and sequestration is required in the international community. In this study, we performed CO₂ emission and shallow-type methane hydrate decomposition experiments at the Joetsu Knoll, offshore Joetsu, Niigata, Japan, as pilot studies to test feasibility of CO₂ sequestration and methane recovery using methane-CO₂ replacement in shallow-type methane hydrates. An isobaric cylinder pump and probe with a built-in heater ("Heat sonde") were developed to inject CO₂ in deep-sea, high-pressure conditions. Before injecting CO₂ into a methane hydrate located in deep-sea sediments, we attempted CO₂ emission directly into deep-seafloor. In the experiment, liquid CO₂ was emitted at the head of Heat sonde, however, the isobaric cylinder pump became clogged during operation. The result reveals that precipitates of CO₂ hydrate, which are generated during mixing of inflow seawater and outflow liquid CO₂, blocked flow lines of the isobaric cylinder pump and Heat sonde. This suggests that our developed instruments must be improved for future work. We also observed the collapse of an exposed methane hydrate layer at the seafloor upon contact with the Heat sonde in our experiment.

  国立研究開発法人海洋研究開発機構, 2015, JAMSTEC Report of Research and Development, 20(0) (0), 61 - 71, Japanese

  [Refereed]

  Research institution


• The Tarama Knoll: Geochemical and Biological Profiles of Hydrothermal Activity

  Toshiro Yamanaka, Hiromi Nagashiov, Ryu Nishio, Kazuna Kondo, Takuroh Noguchi, Kei Okamura, Takuro Nunoura, Hiroko Makita, Kentaro Nakamura, Hiromi Watanabe, Kazuhiro Inoue, Tomohiro Toki, Kouichiro Iguchi, Urumu Tsunogai, Ryoichi Nakada, Shogo Ohshima, Shin Toyoda, Jun Kawai, Naohiro Yoshida, Akira Ijiri, Michinari Sunamura

  Jan. 2015, Subseafloor Biosphere Linked to Hydrothermal Systems: TAIGA Concept, 497 - 504, English

  [Refereed]

  In book


• Distribution and biogeochemical properties of hydrothermal plumes in the rodriguez triple junction

  Takuroh Noguchi, Tatsuhiro Fukuba, Kei Okamura, Akira Ijiri, Katsunori Yanagawa, Michinari Sunamura, Yoshiyuki Ishitani, Teruo Fujii

  Springer Japan, Jan. 2015, Subseafloor Biosphere Linked to Hydrothermal Systems: TAIGA Concept, 195 - 204, English

  [Refereed]

  In book


• Microbial Community Stratification Controlled by the Subseafloor Fluid Flow and Geothermal Gradient at the Iheya North Hydrothermal Field in the Mid-Okinawa Trough (Integrated Ocean Drilling Program Expedition 331)

  Katsunori Yanagawa, Anja Breuker, Axel Schippers, Manabu Nishizawa, Akira Ijiri, Miho Hirai, Yoshihiro Takaki, Michinari Sunamura, Tetsuro Urabe, Takuro Nunoura, Ken Takai

  Oct. 2014, APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 80(19) (19), 6126 - 6135, English

  [Refereed]

  Scientific journal


• Origin and transport of pore fluids in the Nankai accretionary prism inferred from chemical and isotopic compositions of pore water at cold seep sites off Kumano

  Tomohiro Toki, Ryosaku Higa, Akira Ijiri, Urumu Tsunogai, Juichiro Ashi

  Oct. 2014, EARTH PLANETS AND SPACE, 66, English

  [Refereed]

  Scientific journal


• Online oxygen isotope analysis of sub-milligram quantities of biogenic opal using the inductive high-temperature carbon reduction method coupled with continuous-flow isotope ratio mass spectrometry

  Akira Ijiri, Masako Yamane, Minoru Ikehara, Yusuke Yokoyama, Yusuke Okazaki

  Jul. 2014, JOURNAL OF QUATERNARY SCIENCE, 29(5) (5), 455 - 462, English

  [Refereed]

  Scientific journal


• Biological CO2 conversion to acetate in subsurface coal-sand formation using a high-pressure reactor system

  Yoko Ohtomo, Akira Ijiri, Yojiro Ikegawa, Masazumi Tsutsumi, Hiroyuki Imachi, Go-Ichiro Uramoto, Tatsuhiko Hoshino, Yuki Morono, Sanae Sakai, Yumi Saito, Wataru Tanikawa, Takehiro Hirose, Fumio Inagaki

  Dec. 2013, FRONTIERS IN MICROBIOLOGY, 4, English

  [Refereed]

  Scientific journal


• Increase in acetate concentrations during sediment sample onboard storage: a caution for pore-water geochemical analyses

  Akira Ijiri, Yoko Ohtomo, Yuki Morono, Minoru Ikehara, Fumio Inagaki

  2013, GEOCHEMICAL JOURNAL, 47(5) (5), 567 - 571, English

  [Refereed]

  Scientific journal


• Origin of pore water in Kumano mud volcanoes

  TOKI Tomohiro, HIGA Ryosaku, TANAHARA Akira, IJIRI Akira, TSUNOGAI Urumu, ASHI Juichiro

  We used push corers during manned submersible dives to take sediment samples to depths up to 40cm from the third and eighth Kumano Knolls. Boron (B) concentrations in pore water extracted from the sediment samples from the cold seep site were higher than would be explained by organic matter decomposition, suggesting that the pore water at the site was influenced by B derived from smectite-illite alteration. Additionally, the pore water at the cold seep site on the Kumano mud volcano showed high Li concentrations and positive oxygen isotope of pore water. These facts suggest the origin of the pore water would be clay mineral dehydration occurring between 150-160℃. The end-member concentration of B and Li is estimated to be 23±8mmol/kg and 0.8±0.3mmol/kg, respectively. The B/Li ratio of the end-member is evaluated to be 29±14, suggesting these elements would be released from sediment below 200℃. Given the geothermal gradient in this area, this finding suggests that the supplied fluid originates from environment deeper than 3.5km below the seafloor.

  日本地球化学会, 2013, Chikyukagaku, 47(4) (4), 221 - 236, Japanese

  [Refereed]


• Biogeochemical processes involving acetate in sub-seafloor sediments from the Bering Sea shelf break

  Akira Ijiri, Naomi Harada, Akinari Hirota, Urumu Tsunogai, Nanako O. Ogawa, Takuya Itaki, Boo-Keun Khim, Masao Uchida

  Jul. 2012, ORGANIC GEOCHEMISTRY, 48, 47 - 55, English

  [Refereed]

  Scientific journal


• IODP expedition 331: Strong and expansive subseafloor hydrothermal activities in the Okinawa trough

  Ken Takai, Michael J. Mottl, Simon H.H. Nielsen, J. L. Birrien, S. Bowden, L. Brandt, A. Breuker, J. C. Corona, S. Eckert, H. Hartnett, S. P. Hollis, C. H. House, A. Ijiri, J. Ishibashi, Y. Masaki, S. McAllister, J. McManus, C. Moyer, M. Nishizawa, T. Noguchi, T. Nunoura, G. Southam, K. Yanagawa, S. Yang, C. Yeats

  Apr. 2012, Scientific Drilling, (13) (13), 19 - 27

  [Refereed]

  Scientific journal


• Assessment for paleoclimatic utility of terrestrial biomarker records in the Okhotsk Sea sediments

  Osamu Seki, Naomi Harada, Miyako Sato, Kimitaka Kawamura, Akira Ijiri, Takeshi Nakatsuka

  Feb. 2012, DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, 61-64, 85 - 92, English

  [Refereed]

  Scientific journal


• Sea surface temperature changes in the Okhotsk Sea and adjacent North Pacific during the last glacial maximum and deglaciation

  Naomi Harada, Miyako Sato, Osamu Seki, Axel Timmermann, Heiko Moossen, James Bendle, Yuriko Nakamura, Katsunori Kimoto, Yusuke Okazaki, Kana Nagashima, Sergey A. Gorbarenko, Akira Ijiri, Takeshi Nakatsuka, Laurie Menviel, Megumi O. Chikamoto, Ayako Abe-Ouchi, Stefan Schouten

  Feb. 2012, DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, 61-64, 93 - 105, English

  [Refereed]

  Scientific journal


• Methane production and accumulation in the Nankai accretionary prism: Results from IODP Expeditions 315 and 316

  Tomohiro Toki, Yuto Uehara, Kazunari Kinjo, Akira Ijiri, Urumu Tsunogai, Hitoshi Tomaru, Juichiro Ashi

  2012, GEOCHEMICAL JOURNAL, 46(2) (2), 89 - 106, English

  [Refereed]

  Scientific journal


• Inter-laboratory comparison of oxygen isotope compositions from biogenic silica

  Bernhard Chapligin, Melanie J. Leng, Elizabeth Webb, Anne Alexandre, Justin P. Dodd, Akira Ijiri, Andreas Luecke, Aldo Shemesh, Andrea Abelmann, Ulrike Herzschuh, Fred J. Longstaffe, Hanno Meyer, Robert Moschen, Yusuke Okazaki, Nicholas H. Rees, Zachary D. Sharp, Hilary J. Sloane, Corinne Sonzogni, George E. A. Swann, Florence Sylvestre, Jonathan J. Tyler, Ruth Yam

  Nov. 2011, GEOCHIMICA ET COSMOCHIMICA ACTA, 75(22) (22), 7242 - 7256, English

  [Refereed]

  Scientific journal


• Carbon isotope biogeochemistry of acetate in sub-seafloor sediments in the Sea of Okhotsk near Sakhalin Island, Russia

  Akira Ijiri, Naomi Harada, Nanako O Ogawa, Tatsuhiko Sakamoto, Takeshi Nakatsuka

  Biogeochemical processes involving acetate in sub-seafloor sediments were investigated by examining the stable carbon isotopic relationships of acetate and other relevant carbon-bearing materials (i.e., total organic carbon (TOC) and ΣCO_2) in five piston cores retrieved from the Sea of Okhotsk off Sakhalin Island, Russia. The cores were classified into two types on the basis of SO_4^<2-> content: (I) those with sulfate-reducing sediments in which the depletion of pore-water SO_4^<2-> with increasing depth was slight, and (II) those with methanogenic sediments in which SO_4^<2-> concentrations were less than 2mM more than 3m below the seafloor. Acetate was detected in all cores. The acetate content in methanogenic sediments (2.6-23.0μM) was relatively higher than in the sulfate-reducing sediment (2.8-8.8μM). In the sulfate-reducing sediments, the depth profiles of δ^<13>C_ approximately parallel those of δ^<13>C_, with the δ^<13>C_ values (-39‰ to -33‰) depleted by about 12‰ relative to δ^<13>C_ (-24.5‰ to -22.3‰). These approximately parallel depth profiles suggest that the principal acetate production process in the sulfate-reducing sediments is fermentation of dissolved organic compounds. The fermentation products, however, tend to be similar or slightly enriched in ^<13>C compared to their substrates. Therefore, the ^<13>C depletion of acetate relative to TOC in the sulfate reduction zone suggests that some portion of the acetate was synthesized by acetogenesis in which the synthesized acetate is depleted in ^<13>C compared with its precursor. Given the large contribution of land-derived organic matter in the studied sediments, organoautotrophic acetogenesis using the lignin-derived syringate monomer, which originates from land plants, is likely. In the methanogenic sediments, the δ^<13>C_ values in sediments throughout the cores (-39‰ to -25‰) were depleted compared to δ^<13>C_ (-25.5‰ to -21.4‰). This suggests some acetogenic contribution to the total acetate production. The depth profiles of δ^<13>C_ in methanogenic sediments did not parallel those of either δ^<13>C_ or δ^<13>C_<ΣCO2>, probably because of the mixed isotopic effect from some production and consumption processes; namely fermentation, acetogenesis, and acetoclastic methanogenesis.

  The Japanese Association of Organic Geochemists, Dec. 2010, Researches in Organic Geochemistry, 26, 95 - 105, English

  [Refereed]

  Scientific journal


• Enrichment of nitrous oxide in the water columns in the area of the Bering and Chukchi Seas

  A. Hirota, A. Ijiri, D. D. Komatsu, S. B. Ohkubo, F. Nakagawa, U. Tsunogai

  Nov. 2009, MARINE CHEMISTRY, 116(1-4) (1-4), 47 - 53, English

  [Refereed]

  Scientific journal


• Enrichment of adsorbed methane in authigenic carbonate concretions of the Japan Trench

  Akira Ijiri, Urumu Tsunogai, Toshitaka Gamo, Fumiko Nakagawa, Tatsuhiko Sakamoto, Saneatsu Saito

  Oct. 2009, GEO-MARINE LETTERS, 29(5) (5), 301 - 308, English

  [Refereed]

  Scientific journal


• Origin of Fluid in Submarine Mud Volcanoes

  IJIRI Akira

  &emsp;Submarine mud volcanoes are remarkable geological features on the seafloor, which are probably formed by mud breccia extruded from sub-seafloor sediment layers to the seafloor. Most of such volcanoes are found near the continental margin. The driving force of mud volcanism is thought to be unusually high pressure within the deep sedimentary layer and the release of that high pressure. It is important to know the origins of fluids in a mud volcano, because the production of low-density fluid and/or gas production in the deep sedimentary layer has been assumed to be one of the most probable sources of the pressure. Therefore, geochemical studies of pore fluids have been done at various mud volcanoes to identify the fluid origin.<br>&emsp;These studies revealed common chemical characteristics of the fluids, indicating the effects of dehydration of clay minerals. Also, the fluids contain hydrocarbon gases derived from thermocatalyte decomposition of sedimentary organic matter. These characteristics suggest that the mud volcano fluids must originate at a depth in the sedimentary layer greater than 2 km. In some mud volcano fields in the active continental margin, it is proposed that fluid in the mud volcano has migrated through faults from greater depths than the original depth of extruded sediments. Such fluid migration may be another source of high pressure in sedimentary layers.

  公益社団法人 東京地学協会, Jul. 2009, Journal of Geography (Chigaku Zasshi), 118(3) (3), 435 - 454, Japanese

  [Refereed]


• Enrichment of alkanes within a phytoplankton bloom during an in situ iron enrichment experiment in the western subarctic Pacific

  Sohiko Kameyama, Urumu Tsunogai, Fumiko Nakagawa, Motoki Sasakawa, Daisuke D. Komatsu, Akira Ijiri, Junko Yamaguchi, Takeo Horiguchi, Hiroshi Kawamura, Aika Yamaguchi, Atsushi Tsuda

  Jun. 2009, MARINE CHEMISTRY, 115(1-2) (1-2), 92 - 101, English

  [Refereed]

  Scientific journal


• Paleoenvironmental changes in the northern area of the East China Sea during the past 42,000 years

  A Ijiri, LJ Wang, T Oba, H Kawahata, CY Huang, CY Huang

  Apr. 2005, PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 219(3-4) (3-4), 239 - 261, English

  [Refereed]

  Scientific journal


• Characteristics of calcareous concretions with Calyptogena sp. in the Miocene Morai Formation, Hokkaido

  ISHIMURA Toyoho, IJIRI Akira, ABE Kohei, TSUNOGAI Urumu

  The Geological Society of Japan, Mar. 2005, The Journal of the Geological Society of Japan, 111(3) (3), VII - VIII, Japanese

  [Refereed]


• An exceptionally well-preserved fossil seep community from the Cretaceous Yezo Group in the Nakagawa area, Hokkaido, northern Japan

  Yoshinori Hikida, Seiichi Suzuki, Yoshihiro Togo, Akira Ijiri

  Palaeontological Society of Japan, Dec. 2003, Paleontological Research, 7(4) (4), 329 - 342, English

  [Refereed]

  Scientific journal


• A simple method for oxygen-18 determination of milligram quantities of water using NaHCO3 reagent

  A Ijiri, U Tsunogai, T Gamo

  2003, RAPID COMMUNICATIONS IN MASS SPECTROMETRY, 17(13) (13), 1472 - 1478, English

  [Refereed]

  Scientific journal


• Data Report: Authigenic Carbonates at Sites 1150 and 1151

  Akira Ijiri, Tatsuhiko Sakamoto, Urumu Tsunogai, Toshitaka Gamo, Saneatsu Saito, Kiyoshi Suyehiro

  Proceedings of the Ocean Drilling Program, Scientific Results, 186, 12, English

  [Refereed]

  Research society

• 「桧原宿跡」の学術調査-湖底に眠る宿場町と近代日本最大の火山災害の痕跡を探る

  谷川亘, 谷川亘, 山本裕二, 中村璃子, 多田井修, 山本哲也, 井尻暁, 廣瀬丈洋, 木村淳, 山崎新太郎, 吉田昌央

  2024, Isotope News (Web), (793) (793)


• Multi isotope analysis of gas species in geothermal fluids and application to a new geothermometer

  石橋純一郎, 井尻暁

  2022, 岩谷直治記念財団研究報告書, 45


• 海底下の微生物起源ガスとメタンハイドレート（その2）

  稲垣 史生, 井尻 暁

  Dec. 2020, 天然ガス, 6, 21 - 30, Japanese

  [Invited]

  Introduction research institution


• 海底下の微生物起源ガスとメタンハイドレート（その１）

  稲垣 史生, 井尻 暁

  Oct. 2020, 天然ガス, 5, 18 - 27, Japanese

  [Invited]

  Introduction research institution


• Volume 358: NanTroSEIZE Plate Boundary Deep Riser 4: Nankai Seismogenic/Slow Slip Megathrust

  Tobin, H, Hirose, T, Ikari, M, Kanagawa, K, Kimura, G, Kinoshita, M, Kitajima, H, Saffer, D, Yamaguchi, A. Eguchi, N, Maeda, L, Toczko, S, J. Bedford, S. Chiyonobu, T.A. Colson, M. Conin, P.H. Cornard, A. Dielforder, M.-L. Doan, J. Dutilleul, D.R. Faulkner, R. Fukuchi, G. Guérin, Y. Hamada, M. Hamahashi, W.-L. Hong, A. Ijiri, D. Jaeger, T. Jeppson, Z. Jin, B.E. John, M. Kitamura, A. Kopf, H. Masuda, A. Matsuoka, G.F. Moore, M. Otsubo, C. Regalla, A. Sakaguchi, J. Sample, A. Schleicher, H. Sone, K. Stanislowski, M. Strasser, T. Toki, T. Tsuji, K. Ujiie, M.B. Underwood, S. Yabe, Y. Yamamoto, J. Zhang, Y. Sanada, Y. Kido, E. Le Ber, S. Saito, T. Kanamatsu

  International Ocean Discovery Program, 18 Jul. 2020, Proceedings of the International Ocean Discovery Program, English, International magazine, Co-authored internationally


• Preliminary Report Expedition 358: NanTroSEIZE Plate Boundary Deep Riser 4: Nankai Seismogenic/Slow Slip Megathrust

  H. Tobin, T. Hirose, M. Ikari, K. Kanagawa, G. Kimura, M. Kinoshita, H. Kitajima, D. Saffer, A. Yamaguchi, N. Eguchi, L. Maeda, S. Toczko, J. Bedford, S. Chiyonobu, T.A. Colson, M. Conin, P.H. Cornard, A. Dielforder, M.-L. Doan, J. Dutilleul, D.R. Faulkner, R. Fukuchi, G. Guérin, Y. Hamada, M. Hamahashi, W.-L. Hong, A. Ijiri, D. Jaeger, T. Jeppson, Z. Jin, B.E. John, M. Kitamura, A. Kopf, H. Masuda, A. Matsuoka, G.F. Moore, M. Otsubo, C. Regalla, A. Sakaguchi, J. Sample, A. Schleicher, H. Sone, K. Stanislowski, M. Strasser, T. Toki, T. Tsuji, K. Ujiie, M.B. Underwood, S. Yabe, Y. Yamamoto, J. Zhang, Y. Sanada, Y. Kido, E. Le Ber, S. Saito, T. Kanamatsu

  International Ocean Discovery Program, 22 Oct. 2019, International Ocean Discovery Program Preliminary Report, English, International magazine, Co-authored internationally


• Development of simple method for oxygen isotope analysis on microgram quantities of biogenic opal

  井尻 暁

  海洋出版, 2018, 海洋. 号外 = Kaiyo monthly : カラー版, (61) (61), 91 - 96, Japanese


• New scope from research on deep-sea mud volcano

  西尾嘉朗, 井尻 暁

  Jan. 2015, Techno-Ocean News, 55, 1 - 2, Japanese

  [Invited]


• Expedition 323 summary

  K.Takahashi, A.C.Ravelo, C.A.Zarikaian, the Expeditio, Scientists, Ivano Aiello, Hirofumi Asahi, Gretta Bartoli, Beth Caissie, Muhong Chen, Elena Colmenero-Hidalgo, Mea Cook, Kelsie Dadd, Gilles Guèrin, Katrine Husum, Akira Ijiri, Sev Kender, Douglas LaVigne, Tanzhuo Liu, Steve Lund, Christian März, Alan Mix, Maheswar Ojha, Makoto Okada, Yusuke Okazaki, Jonaotaro Onodera, Taou␣k Radi, Tatsuhiko Sakamoto, David Scholl, Zuzanna N. Stroynowski

  2011, Proc. IODP, 323, English


• Structure and cold seep of the Nankai accretionary prism off Kumano-Outline of the off Kumano survey during YK01-04 Leg 2 Cruise-

  芦寿一郎, 倉本真一, 森田澄人, 角皆潤, 後藤秀作, 小島茂明, 岡本拓士, 石村豊穂, 井尻暁, 土岐知弘, 工藤新吾, 浅井聡子, 内海真生

  2002, JAMSTEC 深海研究, 20, 1 - 8, Japanese

• 小豆島沖海底の謎の気泡湧出現象：メタン同位体分析による発生要因の解明

  長谷川 風華, 井尻 暁, 中國 正寿, 岸本 浩二, 山口 一岩, 近藤 文義

  沿岸海洋研究集会, Dec. 2024


• 桧原湖湖底遺跡（桧原宿跡）の堆積物コア解析による遺跡の水没過程と湖の環境変遷の調査

  岩原 ほのか, 井尻 暁, 村山 雅史, 山本 裕二, 山本 哲也, 廣瀬 丈洋, 木村 淳, 中川 栄, 島田 彰広, 中村 璃子, 谷川 亘

  第10回地球環境史学会年会, Nov. 2024


• 炭化水素ガスの炭素安定同位体比を指標とした八丁原地熱地帯の地化学調査

  近谷 優毅, 井尻 暁, 松井 洋平, 石橋 純一郎

  日本地熱学会令和6年東京大会, Nov. 2024


• 喜界島周辺海域における観測地震によるタービダイト層検出の試み―KS-24-4次航海の調査速報―

  中西 諒, 成瀬 元, 喜岡 新, 常岡 廉, 根本 夏林, 藤島 誠也, 佐藤 瑠晟, 天野 敦子, 井尻 暁, 横山 祐典

  日本地質学会第131年学術大会, Sep. 2024


• Upward migration of biogenic methane near the frontal thrust in the Nankai Trough

  Yudai Kobayashi, Akira Ijiri

  Workshop on Slow-to-Fast Earthquakes, Sep. 2024


• Origin of fluid along a plate boundary seismogenic zone estimated by hydrogen and oxygen isotopic compositions of water in fluid inclusion of quartz veins at the Nobeoka Thrust, Southwest Japan

  Kanji Tatsumi, Akira Ijiri, Ryu Uemura, Makoto Otsubo, Minoru Ikehara, Asuka Yamaguchi

  Workshop on Slow-to-Fast Earthquakes, Sep. 2024


• 南大洋大西洋セクターで採取された黄金色藻シスト

  加藤 悠爾, 井尻 暁, 池原 実

  地球惑星科学連合 2024年大会, May 2024


• 炭素安定同位体組成から推定する九州八丁原地熱地帯の炭化水素ガスの起源

  近谷 優毅, 井尻 暁, 松井 洋平, 石橋 純一郎

  日本地球惑星科学連合 2024年大会, May 2024


• 潮岬海底谷の潜航調査に基づく南海付加体発達史の更新と大地震セグメント境界の地質学的実態解明：「よこすか」YK23-10S航海報告

  山口 飛鳥, 福地 里菜, 濱田 洋平, 高下 裕章, 川村 喜一郎, 井尻 暁, 奥田 花也, 浜橋 真理, 照井 孝之介, 細川 貴弘, 辰巳 寛二, 芦 寿一郎, 笠谷 貴史, 木下 正高, 亀尾 浩司, 久保田 好美, 辻 健, 白石 和也, 木村 学

  地球惑星科学連合2024年大会, May 2024


• 南部沖縄トラフ背弧海盆における表層堆積物中の間隙水の化学的及び同位体的特徴

  土岐 知弘, 宮城 裕, 平良 優佳, 宮里 香江, 鹿児島 渉悟, 井尻 暁, 宮嶋 佑典, 新城 竜一, 大坪 誠, 木下 正高, 乗船研究者一同

  地球惑星科学連合2024年大会, May 2024


• 延岡衝上断層周辺に分布する石英脈流体包有物の水の水素･酸素同位体分析による地震性分岐断層深部の水の起源と挙動の解明

  辰巳 寛二, 井尻 暁, 植村 立, 大坪 誠, 池原 実, 山口 飛鳥

  地球惑星科学連合2024年大会, May 2024


• 間隙水Li同位体比を用いた日本海メタンハイドレート分布域での深部流体検出

  宮嶋 佑典, 阪井 康真, 井尻 暁, 山岡 香子, 荒岡 大輔, 井川 怜欧, 吉岡 秀佳

  地球惑星科学連合2024年大会, May 2024


• 日向灘・種子島沖・喜界島沖海底泥火山表層堆積物中の流体の起源

  山田 貫太郎, 土岐 知弘, 大塚 宏徳, 板木 拓也, 村山 雅史, 井尻 暁

  日本地球惑星科学連合 2024年大会, May 2024


• 上越沖メタンハイドレート胚胎域における間隙水の高Cl濃度異常

  阪井 康真, 井尻 暁, 宮嶋 佑典, 吉岡 秀佳

  日本地球惑星科学連合 2024年大会, May 2024


• 海底泥火山群からの溶存態有機物および栄養塩の放出

  吉崎 結衣, 星野 辰彦, 松井 洋平, 川口 慎介, 竹内 誠, 岡村 慶, 野口 拓郎, 乙坂 重嘉, 井尻 暁

  地球惑星科学連合2024年大会, May 2024


• Mapping cyanobacterial biomarkers in modern hot spring stromatolites by MALDI-TOF/MS imaging method

  奥村 知世, 井尻 暁, 齋藤 大樹, 山口 耕生

  地球惑星科学連合2024年大会, May 2024


• 喜界島～日向灘における泥火山分布 -白鳳丸KH-23-4 地物調査速報-

  大塚 宏徳, 井尻 暁, 中西 諒, 福地 里菜, 星野 辰彦, 土岐 知弘, 板木 拓也, 北田 数也, 浅田 美穂, 中尾 眞子, 鈴木 由布, 波多野 泰成, 松下 誠, 辰巳 寛二, 吉本 剛瑠, 乗船研究者

  地球惑星科学連合2024年大会, May 2024


• KH-23-4航海で採取された西南海トラフおよび琉球海溝北部の泥火山噴出物の空隙率

  福地 里菜, 趙 陽, 井尻 暁, 板木 拓也, 吉本 剛瑠, 山口 飛鳥, 村山 雅史, 大塚 宏徳, 土岐 知弘, 星野 辰彦, 乗船研究者

  地球惑星科学連合2024年大会, May 2024


• 琉球海溝・南海トラフ域海底泥火山群におけるプランクトン分布調査

  渡部 裕美, 山本 志乃, Wong Kingsley, Tong Wei, 服部 俊平, 森田 亜美, 井尻 暁

  地球惑星科学連合2024年大会, May 2024


• Discharge and dispersal of deep sub-seafloor microorganisms from mud volcanoes into ocean

  星野 辰彦, 土岐 知弘, 野口 拓郎, 芦 寿一郎, 村山 雅史, 井尻 暁

  地球惑星科学連合2024年大会, May 2024


• Evidence for Archean oxygenic-photosynthesis by 2D mapping by imaging mass spectrometry (MALDI-TOFMS)

  ISHIKAWA Keiichiro, YAMAGUCHI Kosei E, OKUMURA Tomoyo, IJIRI Akira

  Annual Meeting of the Geological Society of Japan, 2024, Japanese, The Geological Society of Japan, 約24億年前、大気中の酸素濃度が爆発的に上昇するGreat Oxidation Event (GOE) が起きたとされている（Holland, 1994; “Early Life on Earth”）。GOE以前の大気中酸素濃度は、現在（約20％）の100万分の１以下、10^–6 atm以下であったと考えられている (Kasting, 1993; Science)。この酸素の起源は、酸素発生型光合成バクテリアであるシアノバクテリア由来のものであるが、当初は大気および海洋中の還元的物質（例：メタン、鉄イオン、硫化物イオン）の酸化に使われたため、すぐに大気中に集積することはなかった。約35億年前のオーストラリア北西部の珪質岩中の炭素の濃集組織が、形態的・化学的特徴からシアノバクテリアの微化石であるとの見方もあるが（Schopf, 1993; Science）、堆積後の非生物的な熱変成作用でも似た同位体組成を持った炭素の濃集体が形成されうることが指摘されている(Braiser et al., 2002; Nature)。一方、約27億年前の黒色頁岩より、シアノバクテリアのバイオマーカー (2α-メチルホパン) が報告された(Brocks et al., 1999; Science)が、これは後の時代の混入（石油の流入や掘削中の混入）である可能性が示唆された（Rasmussen et al., 2008; Nature）。以上のように、シアノバクテリアの誕生を示す地質学的証拠の信頼性は揺らいでるため、酸素発生型光合成の開始時期という初期地球の大気—海洋—生命システムの進化において極めて重要であるこの疑問の回答は、未だ得られていない。GC-MSによる従来型のバイオマーカ―分析では、試料前処理の際に粉末化した岩石から有機溶媒に可溶な有機物を抽出するため、バイオマーカーの岩石中の位置情報が失われる。そのため、バイオマーカーが堆積時の微生物の死骸由来（現地性）のものか、堆積後に石油等の流体として導入された汚染由来なのかが、判断ができない。そこで本研究では、非破壊分析であるイメージング質量分析（iMScope; 原理はMALDI-TOFMS）を地質試料に応用し、位置情報を伴ったバイオマーカーマッピングを高解像度で行うことで、酸素発生型光合成バクテリアの痕跡を探ることにした。2-メチルホパンの標準試料を試料プレート上に滴下した部分にのみ、側鎖が切れて2位のメチル基が置換していると考えられる2-メチルホパンのm/z=368.4のピークが検出された。m/z=368.4と同様の分布を示すピーク（m/z=369.4、340.4、312.3）も検出された。Brocks et al. (1999)では、2-メチルホパンのフラグメントはm/z=191.2 とされてきたが、今回の標準試料測定では、m/z=191.2はわずかしか検出されなかった。これは、本研究のMALDI-TOFMSと従来法のGC-MSでの、有機分子のイオン化の方法の違いによると考えられる。オーストラリア北西部のピルバラで掘削された（現代の風化の影響が極小の）約27億年前の堆積岩試料WRL1（深海性）、RHDH2A（浅海性）、ABDP#10（ストロマトライト炭酸塩岩）を用いて分析を行った結果、全ての試料において、シアノバクテリアのバイオマーカ―であるホパンを示唆するm/z = 368.4が、初生的な堆積構造に沿う局所的な分布を示すことを確認できた。また、2-メチルホパンのフラグメント由来と考えられるm/z=369.4や312,3も、m/z=368.4と同様の平面分布を示していることが確認できた。以上より、2-メチルホパンが堆積時に集積したことが示唆され、つまりは約27億年前の海洋で酸素発生型光合成が行われていたことが強く示唆される。


• Emission of dissolved organic carbon from submarine mud volcanoes off Kikaijima Island, Tanagashima Island and Hyuga-nada, Japan

  吉崎結衣, 星野辰彦, 松井洋平, 川口慎介, 竹内誠, 岡村慶, 野口拓郎, 乙坂重嘉, 井尻暁

  日本地球化学会年会要旨集(Web), 2024


• Origin of fluids in surface sediments of submarine mud volcanoes off Hyuga-nada, Tanegashima Island, and Kikaijima Island.

  山田貫太郎, 土岐知弘, 大塚宏徳, 板木拓也, 村山雅史, 井尻暁

  日本地球化学会年会要旨集(Web), 2024


• 「よこすか」YK23-10S航海報告:潮岬海底谷の潜航調査に基づく南海付加体発達史の更新と大地震セグメント境界の地質学的実態解明

  山口飛鳥, 福地里菜, 濱田洋平, 高下裕章, 川村喜一郎, 井尻暁, 奥田花也, 浜橋真理, 照井孝之介, 細川貴弘, 辰巳寛二, 芦寿一郎, 笠谷貴史, 木下正高, 亀尾浩司, 久保田好美, 辻健, 白石和也, 木村学

  海と地球のシンポジウム発表課題一覧・要旨集(CD-ROM), 2024


• 間隙水および炭化水素ガスの化学・同位体組成から推定される南海トラフ熊野前弧海盆深部の流体移動

  小林 祐大, 井尻 暁, 河合 達也, 石川 剛志

  Japan Geoscience Union Meeting 2023, May 2023


• 日本海上越沖の海底深部掘削コアに見る炭酸塩コンクリーションの初期形成過程

  宮嶋 佑典, 風呂田 郷史, 太田 雄貴, 鈴木 清史, 井尻 暁, 吉岡 秀佳, 天野 敦子, 高橋 浩, 青柳 智, 堀 知行, 佐藤 幹夫

  Japan Geoscience Union Meeting 2023, May 2023


• Single-channel seismic structure of mud volcanoes on the landward slope of Ryukyu Trench off Tanegashima island

  大塚 宏徳, 北田 数也, 井尻 暁, 飯島 耕一, 町山 栄章, 山本 富士夫, 稲垣 史生

  Japan Geoscience Union Meeting 2023, May 2023


• 種子島沖第15海底泥火山の噴出堆積物中から採取されたメタンハイドレートの起源

  山田 貫太郎, 土岐 知弘, 村山 雅史, 井尻 暁

  Japan Geoscience Union Meeting 2023, May 2023


• 種子島沖海底泥火山群からの溶存有機態炭素の放出

  吉崎 結衣, 星野 辰彦, 松井 洋平, 川口 慎介, 井尻 暁

  Japan Geoscience Union Meeting 2023, May 2023


• 桧原湖湖底遺跡の湖底堆積物に記録される自然災害と人工改変

  谷川 亘, 山本 裕二, 山崎 新太郎, 井尻 暁, 廣瀬 丈洋, 木村 淳, 佐々木 蘭貞, 中川 永, 島田 彰広, 山本 哲也

  Japan Geoscience Union Meeting 2023, May 2023


• Updating tectonic evolution of the Nankai accretionary prism and geological structures of the boundary between segments of megathrust earthquakes based on submersible survey along Shionomisaki submarine canyon: Initial report of R/V Yokosuka YK23-10S cruise

  Yamaguchi Asuka, Fukuchi Rina, Hamada Yohei, Koge Hiroaki, Kawamura Kiichiro, Ijiri Akira, Okuda Hanaya, Hamahashi Mari, Terui Konosuke, Hosokawa Takahiro, Tatsumi Kanji, Ashi Juichiro, Kasaya Takafumi, Kinoshita Masataka, Kameo Koji, Kubota Yoshimi, Tsuji Takeshi, Shiraishi Kazuya, Kimura Gaku

  Annual Meeting of the Geological Society of Japan, Sep. 2023, Japanese, The Geological Society of Japan, 世界の沈み込み帯の中で、南海トラフは付加体の発達する代表的な沈み込み帯であり、前弧域の大構造とその発達史の理解は、海溝型地震の発生場、および沈み込み帯のダイナミクスを理解する上で重要である。南海トラフにおける近年の深海掘削・反射法探査の成果をふまえて、東南海・南海地震のセグメント境界付近に位置し、付加体断面が露出する潮岬海底谷沿いの海底地質調査・サンプリングを「しんかい6500」で行うことを目的として、2023年6月15日～23日に「よこすか」YK23-10S航海が行われた。本発表ではその速報結果を報告する。 YK23-10S航海では紀伊半島沖の潮岬海底谷において「しんかい6500」による潜航調査を実施し、南海トラフ付加体および前弧海盆堆積物の採取、プッシュコアラーによる表層堆積物および冷湧水の採取、地形調査・地磁気観測・熱流量観測などの地球物理調査を行った。海底谷の崖沿いに行った4潜航では、付加体を構成すると考えらえる泥岩、斜面堆積盆または前弧海盆最下部をなすと考えられる礫岩、前弧海盆堆積物と考えられる砂岩泥岩互層を視認・撮影し、合計104個・195 kgの岩石試料を採取した。また、礫岩と砂岩泥岩互層の境界露頭を4潜航全てで確認した。今後、石灰質ナンノプランクトンおよび浮遊性有孔虫による年代測定を行い、付加体と前弧海盆の境界の年代を決定することで南海付加体および前弧海盆の発達史を更新できると期待される。海底谷を縦断した1潜航では、「しんかい6500」に搭載したサブボトムプロファイラーによる海底下構造探査とプッシュコア、「よこすか」による海底地形調査を総合し、海底谷の発達過程と物質移動に関する知見が得られた（浜橋ほか、本大会）。Tsuji et al. (2013) は、潮岬海底谷直下に高密度なドーム状岩体が存在することを反射法地震探査から指摘しており、このドーム状岩体は中期中新世の火成複合岩体で、東南海・南海地震の破壊領域にも影響を与える可能性が指摘されている（Kimura et al., 2022）。本航海では、「しんかい6500」に搭載した熱流量測定装置（SAHF）による地殻熱流量測定を9地点で行った。今後、熱流量測定結果、および「よこすか」搭載の三成分磁力計・プロトン磁力計による広域地磁気観測に基づき、火成岩体の存在について多角的に検討を行う予定である。 本航海は海況に恵まれ、予定していた5潜航を完遂することができた。今後、乗船後研究の進展により、南海付加体と熊野海盆の形成初期の発達史、およびセグメント境界の実態を物質科学的に解明することが可能になると期待される。「しんかい6500」による広域の海底調査と大量の試料採取は、反射法地震探査などの地球物理観測と鉛直１次元の深海掘削を、スケールを越えてつなぐ上で非常に強力なツールである。 文献： 浜橋真理ほか，本大会T6セッション；Kimura, G. et al. (2022) Geochemistry, Geophysics, Geosystems, 23, e2022GC010331; Tsuji, T. et al. (2013) Tectonophysics, 600, 52–62.


• Measuring microbial growth and metabolic processes at high hydrostatic pressure and temperature using a novel cultivation system

  諸野祐樹, 森郁晃, 井尻暁, 井尻暁, 西村知泰, 若松泰介, 勝木希, 勝木希

  日本微生物生態学会大会(Web), 2023


• Documentation of channel morphology and backscatter intensity facies along the Shionomisaki Canyon, Nankai Trough, using newly acquired multi-beam bathymetry data and surface sediment cores

  Hamahashi Mari, Koge Hiroaki, Terui Konosuke, Fukuchi Rina, Kawamura Kiichiro, Okuda Hanaya, Yamaguchi Asuka, Hamada Yohei, Ijiri Akira, Tatsumi Kanji, Hosokawa Takahiro

  Annual Meeting of the Geological Society of Japan, 2023, Japanese, The Geological Society of Japan, The geomorphology of submarine channels along the Nankai subduction zone exhibits complex nature that are likely the result of dynamic climatic, tectonic, and oceanic forcings. Submarine canyons are considered to be important passageways for sediment transport from the hinterland and continental shelf, feeding into the trench floor and ocean basin. The Shionomisaki Canyon (SC), with walls of up to ~600 m in height, is a major submarine canyon that has incised into the forearc basin and accretionary prism along the Nankai Trough. The evolution of submarine canyons in active margins and their depositional/incisional processes, however, are yet poorly constrained (Puig et al. 2014). Along the SC, complex forms of sediment waves are inferred, and instability of canyon walls is suggested by multiple scars, gullies, steep flanks and debris flows. During YK23-10S Cruise, high-resolution multi-beam bathymetry data covering ~4600 km² around the full length (upstream to downstream) of the SC was acquired onboard the R/V Yokosuka, using a Kongsberg EM 122 Multi-narrow Beam Echo Sounder, operating at sonar frequencies of 12 kHz, with 432 beams by dual swath, and swath width of 120°. Together with bathymetry survey, sub-bottom profiler data was acquired using the 3300-HM (EdgeTech) Subbottom Profile Subsystem. The motivation of our research is to characterize the seafloor of the contemporary SC using the newly acquired MBES dataset, focusing on the channel morphology and backscatter seismic facies of seafloor sediments. Generally, the intensities of acoustic signals backscattered from the seafloor indicate seafloor characteristics such as interface roughness, acoustic impedance, and surficial heterogeneity, related to seafloor composition, grain size, and small-scale topographies (Lamarche et al. 2011). In this study, we investigate the seafloor sediment distribution from the derived relationship between sediment mean grain size and backscatter angular response. For this purpose, we conduct analyses of facies and grain size using the push core sediments acquired at the channel floor and adjacent terrace surface during the dives of the R/V Shinkai 6500, which provided a unique opportunity to sample seafloor sediments along the SC. Reference: Puig, P. et al (2014), Ann Rev Mar Sci; Lamarche, G. et al (2011), Cont Shelf Res


• Understanding of past ecosystem using environmental DNA remaining in the sediment of Uranouchi Bay, Kochi Prefecture

  星野辰彦, 谷川亘, 井尻暁, 遠山早紀, 村山雅史, 神徳理紗

  日本水環境学会年会講演集, 2023


• 珪藻殻化学分析の高精度化に向けたタクサごとの分離手法の確立

  加藤 悠爾, 諸野 祐樹, 井尻 暁, 寺田 武志, 池原 実

  Japan Geoscience Union Meeting 2022, May 2022

  [Invited]


• 長野県松本市の中部中新統別所層より産出したチューブワーム化石

  延原 尊美, 小池 伯一, 井尻 暁

  Japan Geoscience Union Meeting 2022, May 2022


• 海底下泥火山微生物群集の起源と直上海水との相互作用

  星野 辰彦, 土岐 知弘, 野口 拓郎, 芦 寿一郎, 村山 雅史, 井尻 暁

  Japan Geoscience Union Meeting 2022, May 2022


• Drilling of Mud Volcano in Hyuga-nada: The destination of Seismogenic fluid with Linkage between the activites and subduction dynamics

  福地 里菜, 浅田 美穂, 川村 喜一郎, 山下 幹也, 山下 裕亮, 岩井 雅夫, 井尻 暁, 土岐 知弘

  Japan Geoscience Union Meeting 2022, May 2022


• ベーリング海大陸斜面堆積物中の低温でのスメクタイト—イライト反応 〜微生物代謝活動による反応促進の可能性〜

  井尻暁, 富岡尚敬, 若木重行, 益田晴恵, 小豆川勝美, Kim Sungh, Khim Boo-keum, 村山雅史, 松尾基之, 稲垣史生

  Japan Geoscience Union Meeting 2022, May 2022, Japanese

  [Invited]


• 種子島沖海底泥火山群の総合調査（KS-21-27次航海）速報

  井尻 暁, 土岐 知弘, 村山 雅史, 星野 辰彦, 瀬戸口 亮眞, 満留 由来, 宮本 洋好, 田代 昴士, 安村 幸真, 小林 祐大, 山田 貫太郎, 吉崎 結衣, 大塚 宏徳, 加藤 萌

  Japan Geoscience Union Meeting 2022, May 2022, Japanese

  Oral presentation


• fluid source in the diagenesis of pelagic sediments

  MIZUNO Hitomi, Yamaguchi Asuka, Ijiri Akira, Sano Takashi

  Annual Meeting of the Geological Society of Japan, Sep. 2022, Japanese, The Geological Society of Japan, 沈み込み帯における水の挙動は地震発生に関係していると考えられている。珪質軟泥は、海洋底の年齢が古く海溝の水深が炭酸塩保証深度を超える冷たい沈み込み帯に供給される主要な構成物であり、その脱水がプレート境界断層の発達に関与している可能性がある(Kameda et al., 2012; Kimura te al., 2012)。本研究では日本海溝のような冷たい沈み込み帯における流体の挙動を理解するために、美濃帯犬山セクションをその陸上アナログとして研究した。犬山セクションは分厚い層状チャートが60 m.y.以上の期間にわたって堆積しており、古い海洋プレートの沈み込みで形成されたことを示唆している(Matsuda and Isozaki, 1991)。犬山セクションでは、赤色チャートの層の中に2－10 mおきに白色チャートの層がみられ、これは流体の通り道であったと考えられている(Kameda et al., 2012)。白色チャートを形成するために必要な流体の量は単位質量あたりの珪質軟泥から脱水する水の量よりも明らかに多く (Yamaguchi et al. 2016)、外部からの移流があると考えられる。本研究では冷たい沈み込み帯に供給される流体の起源を制約するため、チャートの露頭や研磨片、薄片の観察を行うとともにチャートの中の様々な沈殿タイミングの石英に対し酸素同位体比と微量元素の分析を行った。チャート中の石英の形態は赤色チャート、白色チャート、石英脈の3つに大別され、また先に述べた順番に沈殿している (Kameda et al., 2012)。本研究では赤色チャート、白色チャート、石英脈中の石英についてそれぞれの酸素同位体比及び微量元素の値を測定し、石英を沈殿させた流体の起源を議論する。 酸素同位体比について、赤色チャート7試料、白色チャート4試料、石英脈3試料の測定をActivation Laboratories Ltd.に依頼した。その結果、赤色チャートはδ18O＝-3.70~10.00‰、白色チャートはδ18O＝-1.00~14.00‰、石英脈はδ18O＝0.55~13.00‰となった。一方、白色チャート3試料について高知コアセンターの酸素同位体分析ライン（Ijiri et al., 2014）で分析したところδ18O＝26.6～25.5‰となった。Kameda et al. 2012の計算によると、日本海溝における石英の沈殿は70℃前後で開始し100～130℃で終了する。同位体平衡の元、70℃及び130℃で石英が沈殿したと仮定すると、流体のδ18OはActivation Laboratories Ltd.で測定された値を採用すると-29.56~-11.86‰ (70℃) 、-21.14~-3.44‰ (130℃) 、高知コアセンターで測定された値を採用すると-0.4~0.7‰ (70℃) 、8.1~9.2‰ (130℃) となる。Activation Laboratories Ltd.のデータから計算された流体のδ18O値は天水、高知コアセンターで測定したデータから計算された流体のδ18O値は海洋地殻やマントルウェッジ由来の、深部からの水が起源であると考えられる。このため、差異が生じた理由を検討し、流体の起源を制約するために微量元素の分析を行う予定である。 引用文献 Ijiri et al., 2014. Journal of Quaternary Science, 29, 455-462. Kameda et al., 2012. Earth Planet. Sci. Lett., 317–318, 136–144. Kimura et al., 2012. Earth Planet. Sci. Lett., 339–340, 32–45. Matsuda, T., Isozaki, Y., 1991. Tectonics, 10, 475–499. Yamaguchi et al., 2016. Tectonophysics, 686, 146–157.


• Purification of disc-shaped diatoms from Southern Ocean sediment by cell sorter and their oxygen isotope analysis

  Ijiri, A, Izumi, T, Morono, Y, Kato, Y, Terada, T, Ikehara, M

  American Geophysical Union 2021, Dec. 2021


• Purification of Disc-Shaped Diatoms from the Southern Ocean Sediment by a Cell Sorter to Obtain an Accurate Oxygen Isotope Record

  Akira Ijiri, Takeshi Izumi, Yuki Morono, Yuji Kato, Takeshi Terada, Minoru Ikehara

  ACS Earth and Space Chemistry, Sep. 2021, American Chemical Society (ACS)


• 堆積物の熱履歴解析による種子島沖泥火山群の噴出機構の解明

  瀬戸口亮眞, 井尻 暁, 山形武靖, 松崎浩之, 萩野恭子, 濱田洋平, 多田井修, 谷川亘, 芦寿一郎, 村山雅史

  日本地質学会第128年学術大会, Sep. 2021


• イメージング質量分析による約27億年前の堆積岩中のバイオ マーカーマッピング

  齋藤大樹, 山口耕生, 井尻 暁, 奥村知世

  日本地質学会第128年学術大会, Sep. 2021


• 南海地震水没伝承「黒田郡」の痕跡発掘に向けた沿岸域海底調査：高知県須崎市野見湾を例に

  谷川亘, 村山雅史, 井尻暁, 廣瀬丈洋, 岡崎啓史, 濱田洋平, 浦本豪一郎, 星野辰彦, 山本裕二, 正木裕香, 徳山英一

  Jun. 2021


• 種子島沖海底泥火山から採取された噴出堆積物の特徴と起源

  瀬戸口亮眞, 井尻暁, 山形武靖, 松崎浩之, 萩野恭子, 芦寿一郎, 村山雅史

  Japan Geoscience Union Meeting 2021, Jun. 2021


• Geochemical study of fumaroles collected from Hatchobaru geothermal field

  石橋純一郎, 井尻暁, 北村圭吾, 藤光康宏

  日本地熱学会学術講演会講演要旨集, 2021


• Oxygen isotope fractionation observed for synthesized amorphous silicate: Implications for the paleo thermometer using diatoms

  河口温子, 堀真子, 成田一人, 井尻暁

  日本地球化学会年会要旨集(Web), 2021


• Origin of the fluid in Taketomi submarine hot spring and estimated temperature of the reservoir

  土岐知弘, 土岐知弘, 新城竜一, 新城竜一, 新垣典之, 原由宇, 満留由来, 安村幸真, 大嶋将吾, 益田晴恵, 井尻暁, 中屋眞司

  日本地球化学会年会要旨集(Web), 2021


• Measuring microbial growth process at high hydrostatic pressure and temperature using a novel cultivation system

  森郁晃, 勝木希, 井尻暁, 井尻暁, 諸野祐樹

  極限環境生物学会誌(Web), 2021


• Preliminary investigation on geochemical distribution of heavy metals in Uranouchi Inlet Bay sediments during the the Anthropocene Epoch

  村山雅史, 谷川亘, 星野辰彦, 井尻暁, 廣瀬丈洋, 新井和乃, 浦本豪一郎, 近藤康生

  Japan Geoscience Union Meeting 2021

• 地球環境史学会


• THE GEOLOGICAL SOCIETY OF JAPAN


• THE GEOCHEMICAL SOCIETY OF JAPAN

• 海底泥火山活動が繋ぐ地圏-水圏-生命圏：深部生命・炭素の海洋拡散過程とその影響

  井尻 暁

  日本学術振興会, 科学研究費助成事業, 基盤研究(A), 神戸大学, 01 Apr. 2024 - 31 Mar. 2029


• Exploration of the limits and adaptations of life in subseafloor biosphere

  諸野 祐樹, 伊藤 元雄, 細川 正人, 加納 英明, 井尻 暁, 阪口 昌彦

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), Japan Agency for Marine-Earth Science and Technology, 01 Apr. 2023 - 31 Mar. 2027


• Clarification of underwater ruins of Lake Hibara and the volcanic disaster that caused the submergence of the lake

  谷川 亘, 山本 裕二, 廣瀬 丈洋, 山崎 新太郎, 井尻 暁, 佐々木 蘭貞, 木村 淳

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), Japan Agency for Marine-Earth Science and Technology, 01 Apr. 2022 - 31 Mar. 2026


• メタン・二酸化炭素凝集同位体温度指標を応用した新しい地化学地熱探査手法の開発

  井尻 暁, 石橋 純一郎, 坂井 三郎, 松井 洋平

  日本学術振興会, 科学研究費助成事業, 挑戦的研究(萌芽), 神戸大学, 30 Jun. 2023 - 31 Mar. 2025


• 非晶質シリカの構造特性が酸素安定同位体温度計に与える影響

  堀 真子, 井尻 暁

  日本学術振興会, 科学研究費助成事業, 基盤研究(C), 大阪教育大学, 01 Apr. 2022 - 31 Mar. 2025


• 石英脈微小流体包有物の直接化学分析によって解き明かす地震発生帯流体の起源と挙動

  井尻 暁

  日本学術振興会, 科学研究費助成事業 学術変革領域研究(A), 学術変革領域研究(A), 神戸大学, 16 Jun. 2022 - 31 Mar. 2024


• 完新世における東南極トッテン氷河の融解と暖水塊流入の影響評価

  板木 拓也, 関 宰, 中山 佳洋, 井尻 暁, 菅沼 悠介, 池原 実

  日本学術振興会, 科学研究費助成事業 基盤研究(B), 基盤研究(B), 国立研究開発法人産業技術総合研究所, 01 Apr. 2021 - 31 Mar. 2024

  近年、南極では外洋の温暖な深層水が棚氷の下面に入り込むことで棚氷の融解/氷床の海への流出の原因となっていることが示されており、巨大氷冠を有する東南極ではトッテン氷河の融解にともなう海水準上昇が懸念されている。しかし、今後起こるとされている融解の加速を現在の海洋観測データだけで検証することは難しく、過去の融解と海洋変動の記録を合わせて評価する必要がある。第61次日本南極地域観測では、2019年11月から2020年3月に砕氷船「しらせ」を用いた採泥調査が実施され、世界に先駆けて東南極トッテン氷河の前縁域から海底コアが採取された。本研究では、海底コアから精密かつ多様な古環境情報を抽出することで、過去の気候変動によって引き起こされた氷河融解の影響を明らかにし、コンピュータによるモデル計算でそのメカニズムに関する理解を得ることを目的とする。調査の空白域である氷河前縁域の理解が進むことによって、南極氷床と海洋がかかわる気候変動・海水準変動の将来予測の精度向上が期待される。本年度は、採取された表層堆積物およびコアの基礎データを取得し、当該海域における堆積物の性状に関する分析を行った。表層堆積物に関しては、1編の論文が受理され、更に1編が執筆中である。今後、これらの情報をコアに応用して、過去の環境変動を検討する。また、モデル計算にかかる境界条件などについて検討を行った。様々な条件での実験と古環境データと比較することで、より確からしいメカニズムを検討する予定である。


• Challenges to deep sea paleoceanography by establishing oxygen isotope proxy of siliceous sponge spicules

  池原 実, 井尻 暁

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kochi University, 01 Apr. 2020 - 31 Mar. 2024

  四国海盆内および周辺海域において本研究に適用できる海底コアとして前年度に選定したトカラ海峡東方のTSK-1PCを主な試料と設定し、コア全体のおよそ300層準から浮遊性有孔虫3種（Globigerinoides ruber、Globigerinoides sacculifer、Globorotalia inflata）を抽出し、質量分析計IsoPrimeにて炭素・酸素同位体比を測定した。また、TSK-1PC の13層準から浮遊性有孔虫の表層種（G. ruber、G. sacculifer）を抽出し、放射性炭素年代を委託分析した（前年度に8層準実施）。その結果、コア最下部（14m）が約6万年前であり、平均堆積速度が約24cm/1000年であった。年代の逆転がなく、タービダイトなどのイベント堆積物もほとんど挟在しないことから、TSK-1PCは古海洋変動研究にとって極めて良質の海底コアであることがわかった。TSK-1PCおよび四国海盆表層堆積物からの珪質海綿骨針の抽出を行い、酸素同位体分析の準備を進めた。また、東シナ海における現生の珪質海綿サンプルの収集を進めた。


• 熱分解炭化水素の同位体システマチクスを決定する

  川口 慎介, 井尻 暁, 上野 雄一郎

  日本学術振興会, 科学研究費助成事業 基盤研究(B), 基盤研究(B), 国立研究開発法人海洋研究開発機構, 01 Apr. 2020 - 31 Mar. 2023

  本研究は、熱分解に起源を有する低分子炭化水素が呈する同位体システマチクスを実験および観測で解明することを目的とする。非生物天体における有機物合成 経路として知られる非生物炭化水素合成(abiotic syntheis)や、嫌気環境で普遍的に見られる微生物メタン生成(microbial methanogenesis)に注目が集まる 中、それら対象に対する「コンタミ」として扱われる熱分解起源炭化水素類の特徴を十分に調査することが、本研究の目的である。本年度は、随伴する炭化水素が熱分解起源である蓋然性の高い温泉付随ガスの採取を行った。具体的には、九州霧島系の火山帯における温泉水ならびに噴気孔において気体成分を採取した。天然に気体成分が分離している地点については、ガラス製の試料採取瓶の内部が十分に試料ガスで置換されるまで採取した。気体成分の分離が困難な温泉水については、事前に真空に排気したガラス製の試料採取瓶に温泉水を吸入し、瓶内の気相に溶存気体を抽出した。採取した試料は、研究分担者である井尻が持ち帰り次第ただちにGC-FIDを用いてLHC濃度を定量し、同位体分析に十分な量が含まれるかを判定した。採取試料の炭素同位体比(13C/12C比)および水素同位体比(D/H比)を海洋研究開発機構横須賀本部で実施した。メタンの多重置換同位体分子組成(13CDH3/12CH4)の分析については井尻が担当し、神戸大学において実施した。分子内部位別同位体組成(13C12C12CH8 / 12C13C12CH8)の分析については、研究分担者である上野が担当する。一連の同位体組成分析に先立って、各種同位体分析の最適条件を検討する実験を各拠点で行った。


• Changes in the environments and biological communities revealed from the sediment core of Uranouchi Inlet Bay, Kochi during Anthropocene

  村山 雅史, 山本 裕二, 星野 辰彦, 新井 和乃, 井尻 暁, 谷川 亘, 近藤 康生

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Kochi University, 01 Apr. 2020 - 31 Mar. 2023

  地球温暖化にともなう海洋環境の変化や人為起源の汚染物質ならびに生態系への影響が強く懸念されており，内湾から採取した連続する堆積物試料の各種解析から，人新世以前と以後との海洋環境の変遷を解明することを目的としている。そのため，精度の高い年代軸を加え，重金属元素，有機・無機炭素，硫黄，酸素量，環境DNAなどの湾内における物質循環と生物生産やその内容，底層の酸化・還元度の変動を数十年単位の時間解像度で定量的に復元し，環境変化の要因，過程，変化の程度，それらの相互作用などを明らかにする。 ダイバーによる海底表層コア（50cm）の直接採取を、浦ノ内湾の湾奥、湾央、湾口の3点で実施した。特に、湾奥と湾口の堆積物表層コアは、シルト質泥であり、X線CT・帯磁率・年代測定の結果から，1900年代以降に連続で堆積していた。XRFコアスキャナーによる連続元素分析では，重金属元素（Cu，Zn，Ni）が，湾奥では，コア表層より約18cm付近から変化し，湾央では，約36．5cm付近からの変化が見られた．これらは、1960年代以降に顕著に増加していた。また，Mnも，同様な深さから減少しており，海底環境が還元的になったと推定される．さらに、EA-IR-MSによる有機物分析から有機炭素量（TOC）と炭素・窒素同位体比は、湾奥コアで約25cm、湾央コアで約45cmから変化しており、養殖がおこなわれた時期以降と一致しており、人為的な影響があったと考えられる． また、多産する貝化石の同定も行い、それらから湾内の生態環境変化について考察中である。 以上の成果については、国際論文（査読有）1本、学会発表3件をおこなった。


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

  井尻 暁, 星野 辰彦, 乙坂 重嘉, 村山 雅史, 土岐 知弘, 野口 拓郎

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kobe University, Apr. 2020 - Mar. 2023

  本研究は、種子島沖海底泥火山群の調査により採取された海水・堆積物試料中の炭素含有物質(メタン、有機物)の炭素安定同位体・放射性炭素同位体分析および微生物叢解析により、泥火山から放出される炭素物質・微生物の起源を明らかにする。また、これら炭素含有物質の海洋中の挙動（拡散、反応過程）を調べ、微生物活動との関連について定量的に把握することにより、泥火山活動を介した地圏-水圏-生命圏の相互作用を解き明かすことを目的とする。 令和2年度に溶存態有機物の濃度・安定・放射性炭素同位体比の測定を行う予定であったが、コロナ禍のために研究が進められなかったた。令和3年度は、TOC計を立ち上げ、海水中溶存態有機炭素濃度の精密測定のプロトコルの作成を行った。この結果、外洋の低濃度溶存態有機炭素濃度を繰り返し測定精度を1%以内におさえる分析手順を確立した。 その他、種子島沖海底泥火山で得られた間隙水、ガス、噴出堆積物の分析をすすめた。堆積物中のビトリナイトの反射率から堆積物の温度履歴を求めた。その結果、堆積物の経験温度は70℃程度であり、泥火山の流体に含まれる熱分解起源炭化水素ガスや、粘土鉱物の脱水由来の水を生成するには経験温度が低いことが明らかになった。このことは、水や炭化水素ガスは、噴出堆積物の起源層よりも深い深度から供給されていることを示唆しており、泥火山の噴出には、泥火山の噴出堆積物起源層への深部流体の注入とそれによる間隙水圧の上昇が寄与している可能性が高いと考えられる。


• 生命の生存限界を探る：海底下高温高圧環境での活動的生命圏の限界と生き残り戦略

  諸野 祐樹, 井尻 暁, 伊藤 元雄, 伊藤 民武, 阪口 昌彦, 星野 辰彦, 山村 雅幸, 若松 泰介

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), Grant-in-Aid for Scientific Research (A), Japan Agency for Marine-Earth Science and Technology, 01 Apr. 2019 - 31 Mar. 2022

  本研究では、生命の存続に必須の「栄養供給」と均衡する生命活動を明らかにするため、海底下地層環境を題材として、そこで連続的、経時的に変化する温度・圧力条件と生命およびその存続について観察することを目的としている。この観察により、地球内部での生命圏限界、または限界をもたらす物理化学的、生理学的因子を解明し、さらに限界生命圏の姿、生命の適応メカニズム、進化学的な議論を展開することを期待している。 本課題では、昨年度までは国際深海科学掘削計画（IODP)におけるグアイマス海盆掘削航海において、高温の熱水が循環し、有機物の現場分解による炭化水素の供給も活発な生命圏から得られた試料において、高感度の生命検出などの第一次分析、および地層試料を現場温度・圧力等、様々な条件で培養する高温高圧培養装置において純粋菌株を用いた培養を実施していた。メタン菌や硫酸還元菌など、高温高圧環境から取得された培養株を用いた試験を実施、常圧環境での培養との挙動の違いなどについての解析を実施したところ、高圧をかけると常圧で実施したこれまでの取得データと異なる培養特性を示した。これはその後の掘削試料を用いた培養の成否に関わる重要なポイントと判断し、研究期間を延長して純粋菌株での高温高圧検証実験を繰り返し、細胞の増殖を確認した。その後、掘削試料を用いた高温高圧実験を延長した研究期間から開始した。延長期間ではまず高温高圧環境下で非生物的に起こる反応の検証を目指し、滅菌済みの試料から炭化水素が遊離してくる様子が観察された。


• Paleoclimate dynamics of the Southern Ocean

  Ikehara Minoru

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Kochi University, 30 Jun. 2017 - 31 Mar. 2022

  The development of a purified method for diatom shells and its oxygen isotope analysis, and the establishment of an automated radiolarian analysis technique using AI deep learning, have successfully brought new developments to paleoceanographic studies in the Southern Ocean. The validity of precise age contrast between marine sediment cores and Antarctic ice cores using dust indices was examined, and it was clarified that local biases such as regional nature of dust variability and contamination of volcaniclastic debris should be fully taken into account in the Indian sector in the Southern Ocean. We reconstructed surface and sub-surface seawater temperature variations in the Indian sector of the Southern Ocean over a wide area, and found that short-term variations are linked to the Southern Annular Mode (SAM), and that marine isotope stages 5e and 9 have significantly higher surface water temperatures than other interglacial stages.


• How the world-largest earthquake occurred at the world-hottest ridge subduction zone? A challenge from geothermal prespective.

  Kinoshita Masataka

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), The University of Tokyo, 01 Apr. 2018 - 31 Mar. 2021

  The research cruise to the world's hottest Chilean Triple Junction (CTJ) was completed in January 2019 to clarify the contribution of the subduction plate thermal structure to the magnitude of subduction-zone earthquakes. It took about 5 days, but shallow reflection survey (4 survey lines), heat flow measurement (6 points), piston coring (6 points), dredge (2 points), and ocean-bottom seismometer installation (13 points). On the seaward side of the ridge axis, at the point uplifted by the normal fault, the deposition rate suddenly changed (fast in the deep part, low in the shallow part) at a depth of about 1 m. The heat flow was 140.210 mW / m2 at the mid-ocean ridge, while it was 370 mW / m2 on the normal fault scarp on the west side and over 230 mW / m2 on the land side (lower part of the accretionary prism slope).


• Marine environments recorded in siliceous microfossil skeletons: species-level analysis of isotopic ratios and minor trace elements

  Takuya Itaki

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), National Institute of Advanced Industrial Science and Technology, 01 Apr. 2018 - 31 Mar. 2021

  Oxygen isotope ratio and trace elements recorded in siliceous microfossil skeletons such as diatoms and radiolarians are expected to be powerful tools for paleoenvironmental studies using sediments from areas or periods where carbonates are not preserved, however what kind of environmental information these values actually indicate is not fully understood. In this study, we developed a system that links the latest technology of automatic sorting and accumulation of fine particles with the automatic classification of microfossils using artificial intelligence, and established a method to accumulate a large amount of siliceous microfossils of a single species. This has paved the way for the analysis of small siliceous microfossils as a single species, which has been difficult in the past.


• Investigation of ancient methane seepage in Sakhalin using silica clathrate minerals

  門馬 綱一, 長瀬 敏郎, ジェンキンズ ロバート, 谷 健一郎, 井尻 暁, 宮脇 律郎

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), National Museum of Nature and Science, Tokyo, 01 Apr. 2016 - 31 Mar. 2021

  シリカクラスレート鉱物とは，結晶構造中にメタンなどの天然ガス分子を含む鉱物である。これまで，産出の極めて稀な鉱物と考えられてきたが，メタン湧水環境において普遍的に産出する可能性が高い。堆積物中の有機物は，地中深くまで運ばれると地熱により分解されてガスとなり，断層や泥火山などの地質構造を通して冷湧水とともに地表（海底）に湧出する。海水中に湧出したガスは微生物に酸化され，最終的には二酸化炭素として再び大気中に放散される。このような地球規模での炭素循環過程を解明する手掛かりとして，シリカクラスレート鉱物は新たな物証を与える。本研究はシリカクラスレート鉱物から古代のメタン湧水環境に関するより詳細な情報を得ることを目的とし，極東ロシア サハリンをモデル地域として研究を行うもので、これまでの調査でサハリン南西部の３ヶ所から、シリカクラスレート鉱物の一種、メラノフロジャイト、およびその仮晶（結晶の形だけを残し，変質したもの）を見出した。 令和元年度は前年度に調査した試料を分析予定であったが、ロシア国外への岩石持ち出し手続きが厳しくなり、試料の入手が遅れたため、次年度に分析予定である。一方、野外調査としては石英の仮晶に注目した対比調査として、九州およびウラジオストク近郊の鉱山等において、シリカクラスレート以外から石英に変質した試料を採取した。また、シリカクラスレート等の精密な結晶構造解析につながる解析技術（最大エントロピー法）の改良について国際学会で発表したほか、シリカクラスレートの一種について共著での論文発表を行った。


• Investigation of birth and evolutional history of photosynthetic organism by biomarker imaging of Achaean rocks

  Ijiri Akira

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Challenging Research (Exploratory), Challenging Research (Exploratory), Japan Agency for Marine-Earth Science and Technology, 29 Jun. 2018 - 31 Mar. 2020

  This study aims to determine when ancient cyanobacteria triggered an increase in the partial pressure of oxygen in the Earth's atmosphere 2.4 billion years ago, and clarifying their environment. Using an imaging mass spectrometry, we succeeded in the high-resolution mapping of hopan, which is a biomarker of bacteria, in the samples of modern cyanobacteria culture strains and cyanobacteria mat, as well as geological samples such as shale and stromatolites from 2.7 billion years ago. Our method of mapping the two-dimensional distribution of biomarkers, may play an important role in discussing the origin of the biomarkers in the Archaean.


• study on the formation and accumulation process of microbial methane by highly sensitive methane clumped isotope analysis

  IJIRI Akira

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Japan Agency for Marine-Earth Science and Technology, 01 Apr. 2017 - 31 Mar. 2020

  We established a high-precision analytical system for the clumped isotope analysis of methane, and performed clumped isotope analysis of methane sampled from the Minami Kanto Natural Gas Field, and found that methane is a microbial-origin methane produced at low temperatures, and that it produces slowly and reaches isotope equilibrium, similar to biogenic methane previously found in subseafloor. Based on the analysis of clumped isotope of methane obtained from the Kumano Basin mud volcano, it was found that more than 90% of the methane in the mud volcano was produced by microorganisms and that the methane production is promoted by the fluid supply.


• Paleoenvironmental reconstruction by imaging mass spectrometry of banded sediment

  IJIRI Akira

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research, Grant-in-Aid for Challenging Exploratory Research, Japan Agency for Marine-Earth Science and Technology, 01 Apr. 2015 - 31 Mar. 2018

  We established the method to analyze a two-dimensional distribution of organic molecules (biomarkers), which is an index of environmental variation contained in single layer of oceanic and lake sediments, by using Imaging Mass Spectrometry. And, by using the method, we tried to analyze geological samples.


• Investigation of subseafloor environments based on methane stable isotopologues

  IJIRI Akira

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Japan Agency for Marine-Earth Science and Technology, 01 Apr. 2014 - 31 Mar. 2017

  We extracted methane from drilled sediment samples from the submarine mud volcano at Kumano basin and the coal-bearing formation off Shimokita. Based on methane clumped isotope, which is a proxy of formation temperature of methane, we revealed the large contribution of microbial methanogenesis in deep subseafloor at both site.


• Estimation of subsidence records and earthquake damages of Nankai earthquakes from the investigation of structures and objects on the seafloor along the Kochi coastline.

  Tokuyama Hidekazu, MURAYAMA Masafumi, YAMAMOTO Yuji, HIROSE Takehiro, IJIRI Akira, HOSHINO Tatsuhiko

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research, Grant-in-Aid for Challenging Exploratory Research, Kochi University, 01 Apr. 2014 - 31 Mar. 2016

  The fate of Kuroda-gori, a coastal village that was submerged under seawater due to subsidence after the Hakuho Earthquake in 684 AD, is widely known in Kochi Prefecture. In addition, structures presumed to be the remnants of historical villages have been observed on the seafloor along the Kochi coastline. This study was conducted to investigate the origin and characteristics of the sub-bottom structures to understand the nature of the land subsidence and elucidate the size of the tsunamis that occurred in Kochi region. We observed the structures at 5 sites on the seafloor near coastline. Our results suggest that structures at Tsumajiro and Nomi-bay areas are artificial, though the structures at Kashiwajima, To-chi, and off-Shiwa areas are probably natural. Stone pillars on the seafloor near Tsumajiro are probably carried by the flow of tsunami waves. Small terrace on the seafloor at Nomi bay area is habitable space and probably submerged due to subsidence after Nankai earthquakes.


• Investigation of microbial conversion process of CO2 in marine sediment-a basic study for carbon dioxide capture and storage-

  IJIRI Akira

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A), Grant-in-Aid for Young Scientists (A), Japan Agency for Marine-Earth Science and Technology, 01 Apr. 2011 - 31 Mar. 2014

  Microbial conversion processes of CO2 in marine sediments were investigated by using the sediment samples obtained by the two drilling cruises. The impact of the CO2 injection to a bituminous coal was also examined by simulating in-situ pressure and temperature using a high-pressure reactor system. The results from these studies suggest that the contribution of homo-acetogenesis from H2/CO2 cannot be ignored as a CO2 conversion process.


• Reconstruction of sub-bottom section of geologic methane-seep site - variety of seep activity indicated by fossil chemosynthetic communities

  NOBUHARA Takami, IJIRI Akira, ISHIMURA Toyoho, MAJIMA Ryuichi, KONDO Yasuo, AMANO Kazutaka, JENKINS Robert

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Shizuoka University, 2011 - 2013

  This study made clear sub-bottom cross-sections of the geological past methane-seep sites in the Eocene Poronai Formation and the Miocene Morai Formation, both of which are bathyal siltstones yielding abundant vesicomyid fossils in Hokkaido, north Japan. Detail observations of their mode of fossil occurrences and seep-carbonate blocks (scale, shape, petrology, and internal textures) indicate that the two seep-sites are contrast in style of seepage activity. The Poronai seep is channelized focused-flow characterized by its fractured lithology due to fluid overpressure, whereas the Morai seep is diffusive and static through interspaces of clotted-mud, without such fracturing texture. These results show that chemosynthetic vesicomyid clams have utilized both types of seepage. This is related with their high mobility in semi-infaunal life position, which can provide a key to solve the question: why they have made success and flourish in the post-Cretaceous age.


• Oxygen isotope measurements on silica in marine sediments from the western North Pacific

  OKAZAKI Yusuke, IJIRI Akira, NAGASHIMA Kana, YAMANE Masako

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Japan Agency for Marine-Earth Science and Technology, 2009 - 2011

  In order to develop a novel quantitative proxy for paleoceanography, we measured oxygen isotopes on silica in marine sediments. Our analytical system is able to measure the oxygen isotopes of small amount of silica(～ 50μg) within analytical errors of+-0.2‰. We measured oxygen isotopes of diatom frustules, radiolarian skeletons and quartz in marine sediments to collect basic data for paleoceanography.


• Development of a simple method for oxygen isotope analysis on microgram quantities of biogenic opal

  IJIRI Akira

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research, Grant-in-Aid for Challenging Exploratory Research, 2009 - 2011

  We developed a rapid and simple method for oxygen isotope analysis on microgram quantities of biogenic opal. The sample size of opal was reduced to<1/10 compared to conventional methods without reducing the precision of the oxygen isotope ratio. We succeeded in the oxygen isotope analysis on monospecific radioralian skeletons by using our new method, and applied the method to analysis for the samples retrieved during Integrated Ocean Drilling Program(IODP) Expeditions.


• Evolution of chemosynthetic communities since the Cretaceous-with special reference to sub-bottom structure of methane-seepage habitats

  NOBUHARA Takami, MAJIMA Ryuichi, AMANO Kazutaka, KONDO Yasuo, SASAKI Taketomo, WADA Hideki, TSUNOGAI Urumu, IJIRI Akira, ISHIMURA Toyoho, JENKINS Robert

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Shizuoka University, 2006 - 2009

  深海底の化学合成群集は,湧水等に含まれるメタンや硫化水素を栄養源とする.化学合成群集は白亜紀以降,その分類構成を変化させたが,その原因は未詳である.本研究は,白亜紀および新生代の化石産地において,岩相や化石相の分布調査,安定同位体比等の分析を行い,湧水場の地下構造を復元した.その結果,新生代に大繁栄したシロウリガイ類は,他の分類群が利用しがたい不安定な湧水を利用していたことが明らかにされた.


• 自生炭酸塩岩の同位体分子指標を用いた沈み込み帯の間隙流体移動の長期観測

  井尻 暁

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Exploratory Research, Grant-in-Aid for Exploratory Research, Japan Agency for Marine-Earth Science and Technology, 2007 - 2008

  海洋プレートの沈み込み帯は、陸源砕屑物の供給や高い生産性により厚い堆積物に覆われている。ここでは、厚い堆積物やプレート沈み込みに伴う高い圧力により、断層や泥ダイアピルを通じて、堆積物中の間隙流体の移動・海底への湧出がおこり、沈み込み帯における物質循環や地震活動に大きな影響を与えていると考えられている。 本研究ではプレート沈み込み帯で形成された自生炭酸塩脈に、新しい「^<13>C-^<18>O結合温度指標」を応用し、炭酸塩脈形成時の流体の温度と酸素同位体比を復元し、海洋プレート沈み込み帯の流体の起源、流路の長期変動について定量的な観測を行うことを目的とする。 今年度は、二酸化炭素の精製システムと「^<13>C-^<18>O結合温度指標」の測定システムが確立されている東京工業大学にて試料の分析を行った。 試料は北海道北部中川町に産出する上部白亜系大曲層の炭酸塩岩を用いた。この地層は過去の海洋プレート沈み込み帯に形成された前弧海盆の堆積物と考えられている。炭酸塩岩はチューブワームなどの化学合成生物化石を含み、炭酸塩岩の炭素同位体比も-40(‰PDB)前後を示すことから、この炭酸塩岩は白亜紀の前弧海盆海底のメタン湧水域において形成されたと考えられる。 炭酸塩の生成温度は,37℃〜44℃(±6℃)と水温が高めで,生成当時の流体の酸素同位体比は,-3.2〜2.6(‰SMOW)と大きな幅を持つ。今後,炭酸塩岩が二次的な変質を受けていないとすると,この炭酸塩岩は,海水よりも温かい水が湧出しているところで生成したと考えられる。この結果から,「^<13>C-^<18>O結合温度指標」は過去の湧水環境の復元のために極めて有効な指標になる可能性が示唆された。

• 二酸化炭素の再資源化方法

  稲垣 史生, 井尻 暁

  特願2013-116581, 03 Jun. 2013, 国立研究開発法人海洋研究開発機構, 特開2014-233248, 15 Dec. 2014, 特許第6202371号, 08 Sep. 2017

  Patent right

  IRI