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<p>Volatiles emitted from black smokers provide crucial insights into mantle and hydrothermal processes. This study investigated the Cheoeum (CVF) and MIRAE-2 (M2VF) vent fields in the 12–16°S region of the Central Indian Ridge (CIR) using RV ISABU and ROV ROPOS. We measured <sup>3</sup>He/<sup>4</sup>He, <sup>4</sup>He/<sup>20</sup>Ne, CH<sub>4</sub> concentration, δ<sup>13</sup>C of CH<sub>4</sub>, and <sup>222</sup>Rn activity in 78 seawater samples from vent fluids and the overlying plume. The end-member <sup>3</sup>He/<sup>4</sup>He ratio is 7.94 Ra, indicating the MORB mantle source. Vent fluids show high CH<sub>4</sub> concentrations (up to 11,578&#xa0;nM/kg) and anomalously heavy δ<sup>13</sup>C values (-11.23 to -7.39 ‰), suggesting abiotic near-quantitative CO<sub>2</sub> reduction in closed-system environments such as olivine-hosted fluid inclusions. Principal Component Analysis distinguished the hydrothermal fluids from background waters by analyzing chemical proxies and spatial information. This first volatile-geochemistry dataset from the CIR provides direct isotopic evidence for mantle-derived helium and abiotic methane, offering a key reference for understanding deep-sea carbon cycling and chemosynthetic ecosystems at slow-spreading ridges.</p>

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Emissions of mantle helium and abiotic methane at newly discovered black smokers along the Central Indian ridge (12°S–16°S)

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月30日

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  • Heejun Kim,
  • Jungpyo Hong,
  • Wonnyon Kim,
  • Jonguk Kim,
  • Guebuem Kim,
  • Urumu Tsunogai,
  • Naoto Takahata,
  • Yuji Sano,
  • Hyunwoo Lee

摘要

Volatiles emitted from black smokers provide crucial insights into mantle and hydrothermal processes. This study investigated the Cheoeum (CVF) and MIRAE-2 (M2VF) vent fields in the 12–16°S region of the Central Indian Ridge (CIR) using RV ISABU and ROV ROPOS. We measured 3He/4He, 4He/20Ne, CH4 concentration, δ13C of CH4, and 222Rn activity in 78 seawater samples from vent fluids and the overlying plume. The end-member 3He/4He ratio is 7.94 Ra, indicating the MORB mantle source. Vent fluids show high CH4 concentrations (up to 11,578 nM/kg) and anomalously heavy δ13C values (-11.23 to -7.39 ‰), suggesting abiotic near-quantitative CO2 reduction in closed-system environments such as olivine-hosted fluid inclusions. Principal Component Analysis distinguished the hydrothermal fluids from background waters by analyzing chemical proxies and spatial information. This first volatile-geochemistry dataset from the CIR provides direct isotopic evidence for mantle-derived helium and abiotic methane, offering a key reference for understanding deep-sea carbon cycling and chemosynthetic ecosystems at slow-spreading ridges.