Chemical studies on venting fluids from submarine plate boundaries (KAIKO-TOKAI Project)

深海底的板块边界，如大洋中脊和板块俯冲带，可以被视为开口或窗口，大量化学成分主要通过海水对流从地球内部上来或下到地球内部。由于喷口流体具有与周围海水完全不同的特性，因此建议这些流体应承担海洋和岩石圈之间化学通量的重要部分。这项研究关注了排放流体中溶解的气体成分，如甲烷、氦气、二氧化碳等，因为它们的浓度和稳定同位素比为我们提供了与孔隙流体行为相关的气体来源的许多有用信息。对于俯冲带的冷渗流，这项研究是1993年至1997年间在南海海槽俯冲带东部成功进行的日法KAIKO-TOKAI项目的一部分。我们采集了许多孔隙流体样品和底层海水进行化学表征。我们还推动了大洋中脊（东太平洋海隆、大西洋中脊、印度洋中脊）、弧后盆地（冲绳海槽、马里亚纳海槽、马努斯盆地）和弧火山（明神丘）等地点海底热液喷口的化学研究。包括时间序列数据在内的积累数据阐明了世界热液活动时空变化的复杂特征。到目前为止，我们已经发表了 29 篇关于该项目的原创论文。本研究的这些结果将作为未来更详细研究的初步数据库发挥重要作用。

Plate boundaries on the deep seafloor, such as mid-oceanic ridges and plate subduction zones, can be regarded as openings or windows through which much amount of chemical components comes up from or goes down to the earth interior chiefly by seawater convection. Since the venting fluids have quite different characteristiecs from ambient seawater, it is suggested that the fluids should bear significant parts of chemical flux between the ocean and the lithosphere. This study has paid attention to dissolved gas components, such as methane, helium, carbon dioxide etc. in venting fluids, because their concentrations and stable isotope ratios give us much useful information on the sources of the gases associated with pore fluid behaviors. As for the cold seepage at subduction zones, this study forms a part of Japan-France KAIKO-TOKAI Project which had been successfully conducted in the eastern Nankai Trough subduction zone between 1993 and 1997. We took many pore fluid samples and bottom seawaters for their chemical characterization. We have also promoted chemical investigations for submarine hydrothermal vents at various locations of mid-oceanic ridges (East Pacific Rise, Mid-Atlantic Ridge, Indian Ridge), back-arc basins (Okinawa Trough, Mariana Trough, Manus Basin), and arc volcanoes (Myojin Knoll). Accumulated data including time-series data have elucidated complicated chatacteristics of spatial and temporal variations of hydrothermal activity in the world. We have published 29 original papers on this project so far. These results of this study will play important role as preliminary databases for more detailed researches in the future.