[B-PT24_29AM1] 化学合成生態系の進化をめぐって

[BPT24-03] 地球年代学と生物多様性解析の融合による熱水系進化解析の試み

*熊谷 英憲¹、渡部 裕美²、矢萩 拓也³、小島 茂明⁴、中井 俊一⁵、豊田 新⁶、石橋 純一郎⁷ (1.海洋研究開発機構海底資源研究プロジェクト、2.海洋研究開発機構、3.東京大学大学院新領域創成科学研究科、4.東京大学大気海洋研究所、5.東京大学地震研究所、6.岡山理科大学理学部応用物理学科、7.九州大学大学院理学研究院地球惑星科学部門)

キーワード：地球年代学, 生物多様性解析, 海底下の大河, 電子スピン共鳴, ウラン-トリウム非平衡, 塩基置換解析

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.