Aerobic biomineralization of Mg-rich carbonates: Implications for natural environments

• Published in: Chemical geology 2011-02, Vol.281 (3), p.143-150
• Main Authors: Sánchez-Román, Mónica, Romanek, Christopher S., Fernández-Remolar, David C., Sánchez-Navas, Antonio, McKenzie, Judith Ann, Pibernat, Ricardo Amils, Vasconcelos, Crisogono
• Format: Article
• Language: English
• Subjects: Bacteria; calcite; calcium; carbon; Carbon isotopes; Carbonates; Culture; Dolomite; Halophilic aerobic bacteria; Huntite; Magnesium; metabolism; Mg-rich carbonates; Microorganisms; organic compounds; Precipitates; Precipitation; Stable carbon isotope; stable isotopes
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/j.chemgeo.2010.11.020

We studied the formation of Mg-rich carbonate in culture experiments using different aerobic bacterial strains and aqueous Mg/Ca ratios (2 to 11.5) at Earth surface conditions. These bacteria promoted the formation of microenvironments that facilitate the precipitation of mineral phases (dolomite, huntite, high Mg-calcite and hydromagnesite) that were undersaturated in the bulk solution or kinetically inhibited. Dolomite, huntite, high Mg-calcite, hydromagnesite and struvite precipitated in different proportions and at different times, depending on the composition of the medium. The Mg content of dolomite and calcite decreased with an increasing Ca concentration in the medium. The stable carbon isotope composition of the Mg-rich carbonate precipitates reflected the isotope composition of the organic compounds present in the media, suggesting that microbial metabolism strongly influenced the carbon isotope composition of biomediated carbonates. We observed that Ca-enriched carbonate precipitates have relatively low carbon isotope composition. These results provide insights into the mechanism(s) of carbonate formation in natural systems, and they are of fundamental importance for understanding modern environments in which carbonate minerals form as a window into the geologic past. [Display omitted] ►Mg-rich carbonates precipitate in aerobic culture experiments. ►Mineral precipitation sequence depends on the ionic composition of the culture medium. ►Microbial metabolism strongly influences the C isotope composition of carbonates. ►Metastable carbonate phases can dissolve, alter or transform to more stable phases.