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Hitoshi Tomaru

Biogeochemistry Group

Department of Earth Sciences

Topics

  • Formation and dissociation of methane hydrates during the Earth's history

  • 129I geochronology for fluid system

Research Subjects

  • Methane hydrates are crystalline compounds composed of water and methane that form at high pressure and low temperature, ubiquitously found along the continental margins. Because of their pressure/temperature-sensitive nature, they have been formed or dissociated in response to the environmental changes during the earth's history. Our research aims to understand the linkage between methane hydrates and past-present-future environmental changes in terms of geochemical and sedimentological techniques.

  • Natural iodine system has a long-lived radioisotope (129I; half-life of 15.7 Myr). The amount of 129I in geological fluids has been useful to determine the age of iodine-rich host sediments, providing a relative-age model for the fluid domain. We apply recently developed 129I geochronology for material transport and/or accumulation via fluid in the shallow geosphere.

Selected Publications

  • Snyder, G.T., Matsumoto, R., Suzuki, Y., Kouduka, M., Kakizaki, Y., Zhang, N., Tomaru, H., Sano, Y., Takahata, N., Tanaka, K., Bowden, S.A., Imajo, T. (2020) Evidence in the Japan Sea of microdolomite mineralization within gas hydrate microbiomes. Nature Scientific Reports, 10, 1876, doi:10.1038/s41598-020-58723-y.
  • Snyder, G.T., Sano, Y., Takahata, N., Matsumoto, R., Kakizaki, Y., Tomaru, H. (2020) Magmatic fluids play a role in the development of active gas chimneys and massive gas hydrates in the Japan Sea. Chemical Geology, 535, 119462, doi:10.1016/j.chemgeo.2020.119462.
  • Yanagawa, K., Shiraishi, F., Tanigawa, Y., Maeda, T., Mustapha, N.A., Owari, S., Tomaru, H., Matsumoto, R., Kano, A. (2019) Endolithic Microbial Habitats Hosted in Carbonate Nodules Currently Forming within Sediment at a High Methane Flux Site in the Sea of Japan. Geosciences, 9, 463, doi:10.3390/geosciences9110463.
  • Owari, S., Tomaru, H., Matsumoto, R. (2019) Long-term, continuous OsmoSampler results for interstitial waters from an active gas venting site at a shallow gas hydrate field, Umitaka Spur, eastern margin of the Japan Sea. Applied Geochemistry, 104, 25–32, doi:10.1016/j.apgeochem.2019.03.011.
  • Ijiri, A., Inagaki, F., Kubo, Y., Adhikari, R. R., Hattori, S., Hoshino, T., Imachi, H., Kawagucci, S., Morono, Y., Ohtomo, Y., Ono, S., Sakai, S., Takai, K., Toki, T., Wang, D. T., Yoshinaga, M. Y., Arnold, G. L., Ashi, J., Case, D. H., Feseker, T., Hinrichs, K.-U., Ikegawa, Y., Ikehara, M., Kallmeyer, J., Kumagai, H., Lever, M.A., Morita, S., Nakamura, K., Nakamura, Y., Nishizawa, M., Orphan, V. J., Roy, H., Schmidt, F., Tani, A., Tanikawa, W., Terada, T., Tomaru, H., Tsuji, T., Tsunogai, U., Yamaguchi, Y. T. and Yoshida, N. (2018) Deep-biosphere methane production stimulated by geofluids in the Nankai accretionary complex. Science Advances, 4, eaao4631, doi:10.1126/sciadv.aao4631.
  • Kano, A., Miyahara, R., Yanagawa, K., Mori, T., Owari, S., Tomaru, H., Kakizaki, Y., Snyder, G., Shimono, T., Kakuwa, Y. and Matsumoto, R. (2017) Gas hydrate estimates in muddy sediments from the oxygen isotope of water fraction. Chemical Geology, 470, 107–115, doi:10.1016/j.chemgeo.2017.08.027.
  • Kouduka, M., Tanabe, A.S., Yamamoto, S., Yanagawa, K., Nakamura, Y., Akiba, F., Tomaru, H., Toju, H. and Suzuki, Y. (2017) Eukaryotic diversity in late Pleistocene marine sediments around a shallow methane hydrate deposit in the Japan Sea. Geobiology, 15, 715–717, doi:10.1111/gbi.12233.
  • Nunoura, T., Takaki, Y., Shimamura, S., Kakuta, J., Kazama, H., Hirai, M., Masui, N., Tomaru, H., Morono, Y., Imachi, H., Inagaki, F. and Takai, K. (2016) Variance and potential niche separation of microbial communities in subseafloor sediments off Shimokita Peninsula, Japan. Environmental Microbiology, 18, 1889–1906, doi:10.1111/1462-2920.13096.
  • Inagaki, F., Hinrichs, K.-U., Kubo, U., Bowles, M. W., Heuer, V. B., Hong, W.-L., Hoshino, T., Ijiri, A., Imachi, H., Ito, M., Kaneko, M., Lever, M. A., Lin, Y.-S., Methe, B. A., Morita, S., Morono, Y., Tanikawa, W., Bihan, M., Bowden, S. A., Elvert, M., Glombitza, C., Gross, D., Harrington, G. J., Hori, T., Li, K., Limmer, D., Liu, C.-H., Murayama, M., Ohkouchi, N., Ono, S., Park, Y.-S., Phillips, S. C., Prieto-Mollar, X., Purkey, M., Riedinger, N., Sanada, Y., Sauvage, J., Snyder, G., Susilawati, R., Takano, Y., Tasumi, E., Terada, T., Tomaru, H., Trembath-Reichert, E., Wang, D. T. and Yamada, Y. (2015) Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor. Science, 349, 420–424, doi:10.1126/science.aaa6882.
  • Hachikubo, A., Yanagawa, K., Tomaru, H., Lu, H. and Matsumoto, R. (2015) Molecular and isotopic composition of volatiles in gas hydrates and in sediment from the Joetsu Basin, eastern margin of the Japan Sea. Energies, 8, 4647–4666, doi:10.3390/en8064647.
  • Tomaru, H. and Fehn, U. (2015) Movement of fluids in the Nankai Trough area: Insights from 129I and halogen distributions along the IODP NanTroSEIZE transect. Geochimica et Cosmochimica Acta, 149, 64–78, doi:10.1016/j.gca.2014.10.028.
  • Miyakawa, A., Saito, S., Yamada, Y., Tomaru, H., Kinoshita, M. and Tsuji, T. (2014) Gas hydrate saturation at Site C0002, IODP Expeditions 314 and 315, in the Kumano Basin, Nankai Trough. Island Arc, 23, 142–156, doi:10.1111/iar.12064.
  • Yanagawa, K., Kouduka, M., Nakamura, Y., Hachikubo, A., Tomaru, H. and Suzuki, Y. (2014) Distinct microbial communities thriving in gas hydrate-associated sediments from the eastern Japan Sea. Journal of Asian Earth Sciences, 90, 243–249.
  • Toki, T., Uehara, Y., Kinjo, K., Ijiri, A., Tsunogai, U., Tomaru, H. and Ashi, J. (2012) Methane production and accumulation in the Nankai accretionary prism: Results from IODP Expeditions 315 and 316. Geochemical Journal, 46, 89–106.
  • Tomaru, H. and Fehn, U. (2012) Data report: Distribution of iodine concentration and 129I in interstitial fluid in the Nankai Trough accretionary prism collected during IODP Expeditions 315 and 316. In Proceedings of the Integrated Ocean Drilling Program, 314/315/316, edited by Kinoshita, M., Tobin, H., Ashi, J., Kimura, G., Lallemant, S., Screaton, E. J., Curewitz, D., Masago, H., Moe, K. T. and the Expedition 314/315/316 Scientists, Integrated Ocean Drilling Program Management International, Inc., Washington, DC, doi:10.2204/iodp.proc.314315316.220.2012.
  • Tomaru, H., Fehn, U., Lu, Z., Takeuchi, R., Inagaki, F., Imachi, H., Kotani, R., Matsumoto, R. and Aoike, K. (2009) Dating of dissolved iodine in pore waters from the gas hydrate occurrence offshore Shimokita Peninsula, Japan: 129I results from the D/V Chikyu shakedown cruise. Resource Geology, 59, 359–373, doi:10.1111/j.1751-3928.2009.00103.x.
  • Tomaru, H., Lu, Z., Fehn, U. and Muramatsu, Y. (2009) Origin of hydrocarbons in the Green Tuff region of Japan: 129I results from oil field brines and hot springs in the Akita and Niigata Basins. Chemical Geology, 264, 221–231, doi:10.1016/j.chemgeo.2009.03.008.
  • Tomaru, H., Lu, Z., Fehn, U., Muramatsu, Y. and Matsumoto, R. (2007) Age variation of pore water iodine in the eastern Nankai Trough, Japan: Evidence for different methane sources in a large gas hydrate field. Geology, 35, 1015–1018, doi:10.1130/G24198A.1.
  • Tomaru, H., Ohsawa, S., Amita, K., Lu, Z. and Fehn, U. (2007) Influence of subduction zone settings on the origin of forearc fluids: Halogen concentrations and 129I/I ratios in waters from Kyushu, Japan. Applied Geochemistry, 22, 676–691, doi:10.1016/j.apgeochem.2006.12.014.

Teaching

General Education Course

  • Basic Laboratory/Field Class of Earth Sciences B

Undergraduate Course

  • Basic Earth Science Seminar
  • Chemistry of the Earth Surface Environment–1, 2
  • Field Class of Geology II
  • Field Class of Snow and Ice Studies
  • Laboratory Class of Geochemistry
  • Laboratory Class of Biogeochemistry
  • Earth Science Seminar
  • Undergraduate Research

Graduate Course

  • Biogeochemistry IV
  • Biogeochemistry V
  • Advanced Seminar I
  • Graduate Research I
  • Advanced Seminar II
  • Graduate Research II

Academic Society Membership

  • Geological Society of Japan
  • Sedimentological Society of Japan
  • Tokyo Geographical Society
  • Geochemical Society of Japan
  • Society of Iodine Science
  • American Geophysical Union
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