Microbial diversity in deep-sea methane seep sediments presented by SSU rRNA gene tag sequencing

http://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk06-03/

Atribacteria from the Subseafloor Sedimentary Biosphere Disperse to the Hydrosphere through Submarine Mud Volcanoes

Submarine mud volcanoes (SMVs) are formed by muddy sediments and breccias extruded to the seafloor from a source in the deep subseafloor and are characterized by the discharge of methane and other hydrocarbon gasses and deep-sourced fluids into the overlying seawater. Although SMVs act as a natural pipeline connecting the Earth’s surface and subsurface biospheres, the dispersal of deep-biosphere microorganisms and their ecological roles remain largely unknown. In this study, we investigated the microbial communities in sediment and overlying seawater at two SMVs located on the Ryukyu Trench off Tanegashima Island, southern Japan. The microbial communities in mud volcano sediments were generally distinct from those in the overlying seawaters and in the well-stratified Pacific margin sediments collected at the Peru Margin, the Juan de Fuca Ridge flank off Oregon, and offshore of Shimokita Peninsula, northeastern Japan. Nevertheless, in-depth analysis of different taxonomic groups at the sub-species level revealed that the taxon affiliated with Atribacteria, heterotrophic anaerobic bacteria that typically occur in organic-rich anoxic subseafloor sediments, were commonly found not only in SMV sediments but also in the overlying seawater. We designed a new oligonucleotide probe for detecting Atribacteria using the catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). CARD-FISH, digital PCR and sequencing analysis of 16S rRNA genes consistently showed that Atribacteria are abundant in the methane plumes of the two SMVs (0.58 and 1.5 × 104 cells/mL, respectively) but not in surrounding waters, suggesting that microbial cells in subseafloor sediments are dispersed as “deep-biosphere seeds” into the ocean. These findings may have important implications for the microbial transmigration between the deep subseafloor biosphere and the hydrosphere

Structure and hydrogeology of the Nankai acnetionary prism

報告番号: 甲08937 ; 学位授与年月日: 1991-03-29 ; 学位の種別: 課程博士 ; 学位の種類: 理学博士 ; 学位記番号: 博理第2413号 ; 研究科・専攻: 理学系研究科地質学専

(Table 1) Remanence properties of discret samples of ODP Holes 126-787B and 126-793B

Samples with vein structures were taken from Sites 787 and 793 in the forearc basin of the Izu-Bonin island arc off Aoga Shima and Sumisu Jima, respectively, between the present volcanic front and the outer arc high. The samples were studied by thin section, X-ray radiograph, and magnetometer; they are discussed with respect to the tectonic implication of the vein structures to the island-arc development. Vein structures are developed in finer, more clayey, preferentially radiolarian-bearing mudstone, subvertical to the bedding plane, which is mostly horizontal. The veins are restricted to certain horizons: in the upper Oligocene at Site 787 and in the lower Miocene at Site 793. The veins are filled with a dominant clay mineral (montmorillonite), which flowed into the vein when the fracture and concomitant stress drop occurred. Some clay mineral was deposited from the fluid that invaded the vein. Some veins might have occurred as hydraulic fractures. The shape, mode of occurrence, and other structural features indicate that the veins originated either as extension fractures or shear cleavages, and then were rotated by the following shearing parallel to the bedding. Sometimes the bedding-parallel slip planes are dislocated by the veins, and sometimes vice versa. This suggests that the vein formation and bedding parallel slip alternately occurred within the same stress environment. Vein attitude was measured by a magnetometer, after alternating field demagnetization; we interpret that they originally formed as subvertical planes, the trends of which average to N45W. The quantity of samples studied was small, but the trends suggest that the stress field for veining might have had a relative extensional stress axis that lay subhorizontally and trended generally northeast. This stress orientation might be attributed to either bending or normal faulting in the forearc basin, at a time when the arc trended northwest

Origin and transport of pore fluids in the Nankai accretionary prism inferred from chemical and isotopic compositions of pore water at cold seep sites off Kumano

We used push corers during manned submersible dives to obtain sediment samples of up to 30 cm from the subseafloor at the Oomine Ridge. The concentrations of B in pore water extracted from the sediment samples from cold seep sites were higher than could be explained by organic matter decomposition, suggesting that the seepage fluid at the site was influenced by B derived from smectite-illite alteration, which occurs between 50°C and 160°C. Although the negative δ18OH2O and δDH2O values of the pore fluids cannot be explained by freshwater derived from clay mineral dehydration (CMD), we considered the contribution of pore fluids in the shallow sediments of the accretionary prism, which showed negative δ18OH2O and δDH2O values according to the results obtained during Integrated Ocean Drilling Program (IODP) Expeditions 315 and 316. We calculated the mixing ratios based on a four-end-member mixing model including freshwater derived from CMD, pore fluids in the shallow (SPF) accretionary prism sediment, seawater (SW), and freshwater derived from methane hydrate (MH) dissociation. However, the Oomine seep fluids were unable to be explained without four end members, suggesting that deep-sourced fluids in the accretionary prism influenced the seeping fluids from this area. This finding presents the first evidence of deep-sourced fluids at cold seep sites in the Oomine Ridge, indicating that a megasplay fault is a potential pathway for the deep-sourced fluids

南海トラフ付加体の構造と水理地質

University of Tokyo (東京大学