The hydrothermal vents distributing along the mid-ocean ridge are geochemical hot-spots playing as a significant source of various elements (e.g., Fe, Mn, Co, Ni, etc.) to sea water, and are characterized by massive biological communities relying on chemosynthetic microbial communities. Although the significance of chemosynthetic processes in the hydrothermal vent ecosystem is well established, microbial and biogeochemical processes around the vent plume are relatively under-represented. We investigated the heterotrophic prokaryotes production (HPP) and microbial community structures associated with the vent plume around the Cheoeum hydrothermal vent system in the central Indian Ocean Ridge. The water in the plume was characterized by high concentrations of Mn (~ 200 nM), Fe (~ 6000 nM) and CH₄ (~ 300 nM). The HPP in the plume (average 9.46 µmol C m^-3 d^-1) was greater than that measured above and below the plume (average 2.34 µmol C m^-3 d^-1) and in the ambient deep water away from the vent sites (average 2.71 µmol C m^-3 d^-1). Molecular analysis revealed that microbial communities consist of diverse chemosynthetic ammonia-oxidizing archaea, sulfur-oxidizing bacteria, metal-oxidizing bacteria and methanotrophs, together with heterotrophic bacteria using S⁰, FeOOH and O₂ as an electron acceptor. Our results suggest that chemosynthetic microbial communities are likely to provide a substantial amount of organic substrates for supporting high HPP. Quantitative estimation on the dark CO₂ fixation to evaluate if it is enough to support the high HPP remains as a question to be solved.

Primary Presenter: Jung-Ho Hyun, Hanyang University (hyunjh@hanyang.ac.kr)

Authors:

Hyeonji Lee, Hanyang University  (guswl837@naver.com)

Jonguk Kim, Korea Institute of Ocean Science and Technology  (jukim@kiost.ac.kr)