[B-PT24_29AM1] Evolution of Chemosynthetic Ecosystem in Earth History

[BPT24-03] A trial on evaluating hydrothermal system evolution using geochronological dating and biological diversity analyses

*Hidenori KUMAGAI¹, Hiromi WATANABE², Takuya YAHAGI³, Shigeaki KOJIMA⁴, Shun'ichi NAKAI⁵, Shin TOYODA⁶, Jun-ichiro ISHIBASHI⁷ (1.Submarine Resources Research Project, JAMSTEC, 2.Japan Agency for Marine-Earth Science and Technology, 3.Graduate School of Frontier Sciences, The University of Tokyo, 4.Atmosphere and Ocean Research Institute, The University of Tokyo, 5.Earthquake Research Institute, University of Tokyo, 6.Department of Applied Physics, Faculty of Science, Okayama University of Science, 7.Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University)

Keywords:geochronology, biodiversity, TAIGA-project, ESR, U-Th disequilibrium, mitochondrial mismatch analysis

To elucidate the evolution of hydrothermal activities, we conducted an interdisciplinary study including geochemistry and biology to develop a method of obtaining reliable age information. Because there was a small amount of constraint on the lifetime of activity at hydrothermal sites, this study is one of the principal goals of the TAIGA-project,"Trans-crustal Advection and In-situ biogeochemical processes of Global sub-seafloor Aquifer" funded by a Grant-in-Aid for Scientific Research on Innovative Areas. As geochemical dating techniques, two methods applicable for hydrothermal ore minerals were developed and improved to fill the gap of the time-ranges in the conventional dating methods: electron spin resonance method and uranium-thorium disequilibrium method. Cross checks between the two methods generally showed good agreement for the range of hundreds to thousands of years. Except for the extreme values for each hydrothermal site, geochemical ages exceed 9ka for the southern Mariana Trough and for 16ka for the Okinawa Trough, respectively. As biological analysis, the biodiversity among faunal communities in the targeted areas was analyzed at the species and DNA levels. In the southern Mariana Trough, Alviniconcha gastropods and Neoverruca barnacles clearly show the greater genetic diversity with greater distances from the ridge axis, which fairly corresponds to the geochemical ages for ore minerals. In the Okinawa Trough, Bathyacmaea limpet showed greater genetic diversity at the Hakurei site in the Izena Hole where the ore minerals show oldest ages among the studied sites (Fig.). Species and genetic diversity of the local fauna were not always correlated to geochemical dating, either in the southern Mariana Trough region or in the Okinawa Trough region. Although the results are not simple, comparison of age information obtained from analyses of these two disciplines potentially provides important constraints for discussion of the history and evolution of hydrothermal activities.Figure caption (upper): Genetic divergence of COI gene indicated as mismatches in base sequences of Bathyacmaea secunda limpet of the Okinawa Trough. Scale bars are shown as five mismatches of partial COI sequences. (lower) Geochemical age range determined from the sulfide and sulfate deposits in Okinawa Trough. Active sites are shown from approximately SW to NE. The left-hand side is the southwestern end. Colored bars represent reliable age ranges for respective sites. The localities are denoted as follows: Yg, Daiyon-Yonaguni Knoll; Ht, Hatoma Knoll; Ir, Irabu Knoll; Izh, Hakurei-site in Izena Hole; Izj, JADE-site in Izena Hole; Ik, Iheya North Knoll; Yr, Yoron Hole; Me, Minami-Ensei Knoll.