EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Uniquely low stable iron isotopic signatures in deep marine sediments caused by Rayleigh distillation

Male Köster1, Michael Staubwasser2, Anette Meixner3,4, Simone A. Kasemann3,4, Hayley R. Manners5, Yuki Morono6, Fumio Inagaki7,8, Verena B. Heuer4, Sabine Kasten1,3,4, and Susann Henkel1,4
Male Köster et al.
  • 1Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany, Marine Geochemistry, Bremerhaven, Germany (
  • 2University of Cologne, Cologne, Germany
  • 3University of Bremen, Faculty of Geosciences, Bremen, Germany
  • 4MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
  • 5School of Geography, Earth and Environmental Sciences, University of Plymouth, Plymouth, United Kingdom
  • 6Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Sciences and Technology (JAMSTEC), Nankoku, Kochi, Japan
  • 7Mantle Drilling Promotion Office, Institute for Marine-Earth Exploration and Engineering (MarE3), JAMSTEC, Yokohama, Japan
  • 8Department of Earth Sciences, Graduate School of Science, Tohoku University, Sendai, Japan

Microbially mediated iron (Fe) reduction is suggested to be one of the earliest metabolic pathways on Earth and Fe(III)-reducing microorganisms might be key inhabitants of the deep and hot biosphere [1, 2]. Since microbial Fe cycling is typically accompanied by Fe isotope fractionation, stable Fe isotopes (δ56Fe) are used as tracer for microbial processes in modern and ancient marine sediments [3, 4]. Here we present Fe isotope data for dissolved and sequentially extracted sedimentary Fe pools from subseafloor sediments that were recovered during International Ocean Discovery Program Expedition 370 from a 1,180 m deep hole drilled in the Nankai Trough off Japan where temperatures of up to 120°C are reached at the sediment-basement interface. The expedition aimed at exploring the temperature limit of microbial life and identifying geochemical and microbial signatures that differentiate the biotic and abiotic realms [5, 6]. Dissolved Fe (Fe(II)aq) is isotopically light throughout the ferruginous sediment interval but some samples have exceptionally light δ56Fe values. Such light δ56Fe values have never been reported in natural marine environments and cannot be solely attributed to microbially mediated Fe(III) reduction. We show that the light δ56Fe values are best explained by a Rayleigh distillation model where Fe(II)aq is continuously removed from the pore water by diffusion and adsorption onto Fe (oxyhydr)oxide surfaces. While the microbially mediated Fe(II)aq release has ceased due to an increase in temperature beyond the threshold of mesophilic microorganisms, the abiotic diffusional and adsorptive Fe(II)aq removal continued, leading to uniquely light δ56Fe values. These findings have important implications for the interpretation of Fe isotope records especially in deep subseafloor sediments.



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[4] Anbar, A.D. and Rouxel, O., 2007. Annu. Rev. Earth Planet. Sci. 35: 717-746.

[5] Heuer, V.B. et al., 2017. In Proc. IODP Volume 370.

[6] Heuer, V.B. et al., 2020. Science 370: 1230-1234.

How to cite: Köster, M., Staubwasser, M., Meixner, A., Kasemann, S. A., Manners, H. R., Morono, Y., Inagaki, F., Heuer, V. B., Kasten, S., and Henkel, S.: Uniquely low stable iron isotopic signatures in deep marine sediments caused by Rayleigh distillation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6603,, 2023.