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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-449
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-449
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Dec 2019

Submitted as: research article | 05 Dec 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Authigenic formation of Ca-Mg carbonates in the shallow alkaline Lake Neusiedl, Austria

Dario Fussmann1, Avril Jean Elisabeth von Hoyningen-Huene2, Andreas Reimer1, Dominik Schneider2, Hana Babková3, Robert Peticzka4, Andreas Maier4, Gernot Arp1, Rolf Daniel2, and Patrick Meister3 Dario Fussmann et al.
  • 1Geobiology, Geoscience Centre, Goldschmidtstraße 3, Georg-August-University Göttingen, 37077 Göttingen, Germany
  • 2Genomic and Applied Microbiology Genomics Laboratory, Institute of Microbiology and Genetics, Grisebachstraße 8, Georg-August-University Göttingen, Göttingen, 37077 Germany
  • 3Department of Geodynamics and Sedimentology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria
  • 4Department of Geography and Regional Research, University of Vienna, Althanstraße 14, 1090 Vienna, Austria

Abstract. Despite advances regarding the microbial and organic-molecular impact on nucleation, the formation of dolomite in sedimentary environments is still incompletely understood. Since 1960, apparent dolomite formation has been reported from mud sediments of the shallow, oligohaline and alkaline Lake Neusiedl, Austria. To trace potential dolomite formation or diagenetic alteration processes in its deposits, lake water samples and sediment cores were analyzed with respect to sediment composition, hydrochemistry and bacterial community composition. Sediments comprise 20 cm of homogenous mud with 60 wt % carbonate, which overlie dark-laminated consolidated mud containing 50 wt % carbonate and plant debris. Hydrochemical measurements reveal a shift from oxic lake water with pH 9.0 to anoxic sediment pore water with pH 7.5. A decrease in SO42− with a concomitant increase of ΣH2S and NH4+ from 0–15 cm core depth, indicates anaerobic heterotrophic decomposition, including sulfate reduction. The bacterial community composition reflects the zonation indicated by the pore water chemistry, with a distinct increase of fermentative taxa below 15 cm core depth.

The water column is highly supersaturated with respect to (disordered) dolomite and calcite, whereas saturation indices of both minerals rapidly approach zero in the sediment. Notably, the relative proportions of different authigenic carbonate phases and their stoichiometric compositions remain constant with increasing core depth. Hence, evidence for Ca-Mg carbonate formation or ripening to dolomite is lacking within the sediment of Lake Neusiedl. As a consequence, precipitation of high-magnesium-calcite (HMC) and very-high-magnesium-calcite (VHMC) does not occur in association with anoxic sediment and sulfate reducing conditions. Instead, analytical data for Lake Neusiedl suggest that authigenic HMC and VHMC precipitate from the supersaturated, well-mixed aerobic water column. This observation supports an alternative concept to dolomite formation in anoxic sediments, comprising Ca-Mg carbonate precipitation in the water column under aerobic and alkaline conditions.

Dario Fussmann et al.
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Dario Fussmann et al.
Dario Fussmann et al.
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Short summary
Dolomite [CaMg(CO3)2] is supersaturated in many aquatic settings (e.g. sea water) on modern earth, but does not precipitate directly from the fluid. A fact, known as the dolomite problem. The widely acknowledged concept of dolomite precipitation involves microbial extracellular polymeric substances (EPS) and anoxic conditions as important drivers. In contrast, results from Lake Neusiedl support an alternative concept of Ca-Mg carbonate precipitation under aerobic and alkaline conditions.
Dolomite [CaMg(CO3)2] is supersaturated in many aquatic settings (e.g. sea water) on modern...
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