EGU21-1890, updated on 10 Jan 2023
EGU General Assembly 2021
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Mn(II) carbonate authigenesis marks the benthic SMTZ and is fueled by Mn-driven anaerobic oxidation of methane: A Black Sea evidence

Tiantian Sun1,2, Michael E Böttcher1,3,4, Jens Kallmeyer5, Tina Treude6, Marko Lipka1, Iris Schmiedinger1, Sebastian Eckert7, Rolf Wehausen7, Bo B Jørgensen8, and Francisca Martinez-Ruiz9
Tiantian Sun et al.
  • 1Leibniz Institute for Baltic Sea Research, Geochemistry and Isotope Biogeochemistry Group, Warnemunde, Germany (
  • 2Ocean College, Zhejiang University, Zhoushan, P.R. China.
  • 3Marine Geochemistry, University of Greifswald, Germany
  • 4Interdisciplinary Faculty, University of Rostock, Germany
  • 5Geomicrobiology, GFZ Potsdam, Germany
  • 6Marine Geomicrobiology, University of California,Los Angeles, USA
  • 7ICBM, Microbiogeochemistry, University of Oldenburg, Germany
  • 8Max Planck Institute for Marine Microbiology, Biogeochemistry, Bremen, Germany
  • 9Instituto Andaluz de Ciencias de la Tiera (CSIC-UGR), Facultad de Ciencias, Granada, Spain

In the Black Sea, sediment cores covering the last brackish-limnic transition were recovered and investigated for anaerobic biogeochemical processes controlling sulfur, carbon, and metal cycling. The development of a sulfate-methane transition zone (SMTZ) is nowadays found below the brackish zone in the limnic part of the sediments that limits the upward migration of biogenic methane into surface sediments and the water column. The position of the SMTZ may have changed in the past due to dynamic fluxes of dissolved species in the pore water. Besides dissolved sulfate, metal-bearing minerals have been shown to serve as potential reactants, also converting CH4 into dissolved inorganic carbon (DIC). The pore water and sediment stable isotope (C, S, O) and geochemical composition were investigated, as well as in-situ microbial rates of sulfate reduction and total anaerobic oxidation of CH4 (AOM) obtained from sediment incubations for the identification of a potential contribution of manganese-bearing minerals to AOM in the limnic part of the sediments (Mn-AOM). In the limnic Black Sea sediments Mn-AOM is causes an upward flux of dissolved Mn whereas intense SO4-AOM located in shalower sediments leads to an increase in pH and a maximum in DIC concentrations in the SMTZ. The resulting change in saturation states leads to the precipitation of mixed MnCa-carbonate solid-solutions (‘rhodochrozitization front’) and the development of a zone enriched in excess sedimentary Mn(II). We further argue that these authigenic fronts may survive changes in pore water composition and are stable in the anoxic sedimentary record, marking the position of paleo-SMTZs. The persisting formation of this geochemical marker has advantage in application over the transient development of a sulfidization front of metastable mackinawite, that is fromed by the reaction of downard migrating sulfide with upward diffusing Fe(II), originating from SO4-AOM and Fe-AOM, respectively.

How to cite: Sun, T., Böttcher, M. E., Kallmeyer, J., Treude, T., Lipka, M., Schmiedinger, I., Eckert, S., Wehausen, R., Jørgensen, B. B., and Martinez-Ruiz, F.: Mn(II) carbonate authigenesis marks the benthic SMTZ and is fueled by Mn-driven anaerobic oxidation of methane: A Black Sea evidence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1890,, 2021.

Corresponding displays formerly uploaded have been withdrawn.