Interdisciplinary studies: Introduction of TAIGA concept

After the discovery of seafloor hydrothermal venting, it became evident that the subseafloor fluid advection system plays an extremely important role in the Earth’s element cycle. We designate these fluid advections as sub-seafloor TAIGAs (which stand for Trans-crustal Advection and In-situ biogeochemical processes of Global sub-seafloor Aquifers. In Japanese, “taiga” refers to “a great river”). This concept emphasizes dynamic signature of subseafloor hydrosphere, especially for a hydrothermal fluid circulation system that might support subseafloor microbial ecosystem. However, the link between the fluid advection and microbial activity has never been clearly demonstrated. Wetherefore hypothesized four types of sub-seafloor TAIGAs; hydrogen, methane, sulfur, and iron to investigate the relation. Each type of TAIGA is characterized by the most dominant reducing substance available for chemosynthesis. Our trans-disciplinary research between 2008 and 2012 indicates that the hypothesis is valid and the microbial activity within the flow of TAIGAs has strong linkage to chemical characteristics of each TAIGA; that is, the subseafloor TAIGA supplies four different kinds of electron donor for respective chemolithoautotroph ecosystem which is suitable for particular electron donor. It is also shown that the composition of dissolved chemical species in the subseafloor TAIGAs are substantially affected by the geological background of their flow path such as volcanism, surrounding host rocks and tectonic settings. Our research clearly indicates that the chemosynthetic sub-seafloor biosphere is controlled and supported by Earth’s endogenous flux of heat and mass beneath the seafloor.