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

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.The Swiss Science National Foundation (SNF) is acknowledged for its financial support through Grant No. 20-067620 and 20-105149. This study also received support from the NASA's Astrobiology Institute and the European Science Foundation (ESF) through Grant ArchEnviron No. 2650. DFR and RAP acknowledge support grants AYA-2009-11681 from MICINN (Spain) and 2503050-IPBSL from ERC. ASN acknowledges funding support CGL-2009-09249 and CGL-2007-66744-CO2-01 from MEC (Spain)Peer reviewe