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<p>Hydrothermal systems at ultraslow-spreading mid-ocean ridges remain poorly characterized, particularly where sedimentary and ultramafic influences intersect. Here we present geochemical analyses of vent fluids collected in 2024 from the Jøtul hydrothermal field on the northern Knipovich Ridge. Major element concentrations, dissolved gases, and thermodynamic modeling are used to investigate fluid-rock interactions. The fluids exhibit exceptionally high CH<sub>4</sub> concentrations, that exceed those at the Guaymas Basin, and display characteristics typical of sediment-hosted hydrothermal systems, indicating thermal decomposition of organic matter in clastic sediments. In contrast, high H<sub>2</sub> (&gt;15 mM) and low H<sub>2</sub>S concentrations are more typical of ultramafic-hosted fluids, while geological evidence indicates that the vent field lies atop a detachment fault. Thermodynamic modeling suggests that these high H<sub>2</sub>/H<sub>2</sub>S ratios may result solely from degradation of organic matter followed by abiotic CH<sub>4</sub> oxidation at ~400 °C, rather than from reactions with ultramafic rocks. These results expand the known diversity of sediment-hosted vent fluid compositions and highlight fluid-sediment interaction as an underestimated source of carbon and hydrogen.</p>

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High H2 production in sediment-hosted hydrothermal fluids at an ultraslow spreading mid-ocean ridge

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月6日

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  • Alexander Diehl,
  • Eirini Anagnostou,
  • Patrick Monien,
  • Thomas Pape,
  • Eva-Maria Meckel,
  • Miriam Römer,
  • Leila Mezri,
  • Wolfgang Bach,
  • Donata Monien,
  • Christian Hansen,
  • Aaron Röhler,
  • Katharina Streuff,
  • Sabina Strmic Palinkas,
  • Yann Marcon,
  • Ines Barrenechea Angeles,
  • Charlotte Kleint,
  • Stig‑Morten Knutsen,
  • Gerhard Bohrmann

摘要

Hydrothermal systems at ultraslow-spreading mid-ocean ridges remain poorly characterized, particularly where sedimentary and ultramafic influences intersect. Here we present geochemical analyses of vent fluids collected in 2024 from the Jøtul hydrothermal field on the northern Knipovich Ridge. Major element concentrations, dissolved gases, and thermodynamic modeling are used to investigate fluid-rock interactions. The fluids exhibit exceptionally high CH4 concentrations, that exceed those at the Guaymas Basin, and display characteristics typical of sediment-hosted hydrothermal systems, indicating thermal decomposition of organic matter in clastic sediments. In contrast, high H2 (>15 mM) and low H2S concentrations are more typical of ultramafic-hosted fluids, while geological evidence indicates that the vent field lies atop a detachment fault. Thermodynamic modeling suggests that these high H2/H2S ratios may result solely from degradation of organic matter followed by abiotic CH4 oxidation at ~400 °C, rather than from reactions with ultramafic rocks. These results expand the known diversity of sediment-hosted vent fluid compositions and highlight fluid-sediment interaction as an underestimated source of carbon and hydrogen.