Microbiological Investigation of the Iron-Containing Floculent Mats in Various Deep Sea Environments

Conference abstract (August 14-19, 2011, Goldschmidt 2011 in Prague, Czech Republic)http://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt10-13_leg2/ehttp://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk10-10/

各地の深海底に存在する褐色変色域での微生物調査

BE11-P72ポスター要旨 / ブルーアース2011（2011年3月7日～8日, 東京海洋大学品川キャンパス）http://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt05-18/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt10-06_leg2/ehttp://www.godac.jamstec.go.jp/darwin/cruise/natsushima/nt10-13_leg2/ehttp://www.godac.jamstec.go.jp/darwin/cruise/yokosuka/yk10-10/

Comparative Analysis of Microbial Communities in Iron-Dominated Flocculent Mats in Deep-Sea Hydrothermal Environments

It has been suggested that iron is one of the most important energy sources for photosynthesis-independent microbial ecosystems in the ocean crust. Iron-metabolizing chemolithoautotrophs play a key role as primary producers, but little is known about their distribution and diversity and their ecological role as submarine iron-metabolizing chemolithotrophs, particularly the iron oxidizers. In this study, we investigated the microbial communities in several iron-dominated flocculent mats found in deep-sea hydrothermal fields in the Mariana Volcanic Arc and Trough and the Okinawa Trough by culture-independent molecular techniques and X-ray mineralogical analyses. The abundance and composition of the 16S rRNA gene phylotypes demonstrated the ubiquity of zetaproteobacterial phylotypes in iron-dominated mat communities affected by hydrothermal fluid input. Electron microscopy with energy-dispersive X-ray microanalysis and X-ray absorption fine structure (XAFS) analysis revealed the chemical and mineralogical signatures of biogenic Fe-(oxy)hydroxide species and the potential contribution of Zetaproteobacteria to the in situ generation. These results suggest that putative iron-oxidizing chemolithoautotrophs play a significant ecological role in producing iron-dominated flocculent mats and that they are important for iron and carbon cycles in deep-sea low-temperature hydrothermal environments

Diversity of fluid geochemistry affected by processes during fluid upwelling in active hydrothermal fields in the Izena Hole, the middle Okinawa Trough back-arc basin

Two active hydrothermal fields, Jade and Hakurei fields have been discovered within the Izena Hole, a rectangular 6 km × 3 km shape depression located in the middle Okinawa Trough back arc basin. In both fields, intense hydrothermal activity is represented by venting of high-temperature fluid (>300°C) and occurrence of sulfide/sulfate ore deposits. We collected hydrothermal fluids during dive expeditions of ROV Hyper Dolphin conducted in 2003, 2010 and 2011, in order to analyze both elemental and gas species. The geochemistry of high temperature hydrothermal fluids collected from the Jade and Hakurei fields is very similar to each other with exceptions in minor gas composition. Little temporal variation was observed in geochemistry of the high-temperature hydrothermal fluid of the Jade field over two decades, since a previous study carried out in 1989. These results suggest that these fluids are derived from a common fluid reservoir where fluid chemistry is basically controlled by fluid-mineral equilibria and gas species are dominantly contributed from the same magma. Venting of low temperature fluid (about 104°C) was discovered in the distal part of the Jade field, which was named as the Biwako vent. Chemical composition of the Biwako vent fluid was distinctive from that of the high temperature fluid in the proximal part of the Jade field, and could not be explained by simple dilution or cooling. This intra-field chemical diversity could be caused by phase separation and segregation during fluid upwelling, based on relationships in concentrations of Cl and major cations. On the other hand, the chemical diversity recognized in minor gas composition between the Jade and Hakurei fields is in accordance with results from previous plume survey. Difference in concentrations of minor gases such as H2 is attributed to contribution from thermal degradation of organic matter in the sediment, during fluid upwelling