[A-OS16] Physical, biogeochemical, and ecological processes and variability in the Indian Ocean

[AOS16-P04] Fe-rich, S-depleted hydrothermal sediments at the newly discovered high-temperature Mirae-2 vent field, Central Indian Ridge

*Hanbeom Park¹、Yun Jae Kim²、Jonguk Kim³、Kiho Yang^1,4、Hyeonho An^3,4、Teddy Namirimu²、Yongmoon Lee⁵、Kitae Kim⁶、Hyun Young Chung⁶、Hyunwoo Lee⁷、Sun Ki Choi³、Young Kyu Park⁶、Jaewoo Jung^3,8 (1.Institute for Future Earth, Pusan National University、2.Marine Biotechnology & Bioresource Research Department, Korea Institute of Ocean Science & Technology、3.Ocean Georesources Research Department, Korea Institute of Ocean Science & Technology、4.Department of Oceanography, Pusan National University、5.Department of Geological Sciences, Pusan National University、6.Korea Polar Research Institute、7.School of Earth and Environmental Sciences, Seoul National University、8.Ocean Science, KIOST School, University of Science and Technology)

キーワード：Indian Ocean, Mirae-2 vent field, mineralogy, S-depleted sediment

The newly discovered Mirae-2 vent field, located at a depth of 3,300 m on the slow spreading Central Indian Ridge (14–15°S), commonly composed of Fe-rich basaltic substrate, is characterized as a high-temperature vent field. Samples were collected using remotely operated vehicle ROPOS to investigate the mineralogical, geochemical, and biological characteristics of the uppermost layer of the hydrothermal sediment and the microbial mat around the high-temperature Mirae-2 vent site. The results reveal that the Mirae-2 vent field sediments are iron-enriched but exhibit significant depletion of sulfur and other metal elements. The mineral assemblages indicate abundance of iron-oxide/oxyhydroxide and minor components of calcium carbonates and feldspar in sediments, while vent chimney structures are abundant in metal sulfides. Overall, the geochemical results indicate that the hydrothermal sediment and the microbial mat are significantly affected by hydrothermal processes, rather than being of lithogenic or pelagic origin. The microbial diversity within the hydrothermal sediment and the microbial mat is predominantly composed of Gammaproteobacteria and Alphaproteobacteria, which are frequently observed representative microbes in hydrothermal vent systems. The low concentrations of metals (except for iron) and sulfur relative to other hydrothermal vent fields may be attributed to local current effects and sub-seafloor mixing of the hydrothermal fluid with ambient seawater. The discovery of a new vent field, particularly with its sulfur-depleted hydrothermal sediments, provides valuable insights into the characteristics and ecological dynamics of hydrothermal systems in the Indian Ocean.