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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

Does carbon dioxide storage by cyanobacteria induce biomineralization in presence of basaltic glass?

Thomas Ferrini, Olivier Grandjouan, Olivier Pourret, Raul E. Martinez
Geochemical Journal, Vol. 55, No. 2, P. 51-58, 2021

ABSTRACT

Cyanobacteria induced biomineralization of atmospheric CO2 is a natural process leading to the formation of carbonates by spontaneous precipitation or through the presence of nucleation sites, under supersaturated conditions. As importance of basaltic rocks in the carbon cycle has already been highlighted, basaltic glass was chosen to test its ability to release cations needed for carbonate formation in presence of Synechococcus sp. cyanobacteria. Active cyanobacteria were expected to generate a local alkaline environment through photosynthetic metabolism. This process produces oxygen and hydroxide ions as waste products, raising the pH of the immediate cell surface vicinity and indirectly enhancing the carbonate CO32- concentration and providing the a degree of saturation that can lead to the formation of calcite CaCO3 or magnesite MgCO3. In the presence of active cells, the saturation index (SI) increased from -10.56 to -9.48 for calcite and from -13.6 to -12.5 for magnesite, however they remained negative due to the low Ca2+ and Mg2+ activities. Dead cells were expected to act as nucleation sites by the stepwise binding of carbonate with Ca2+ and Mg2+ on their surface. In the presence of inactive cells, SI values were closer to 0 but still negative due to the low pH and cation concentrations. Our results highlight that our current understanding of the carbon cycle suggests that Earth’s climate is stabilized by a negative feedback involving CO2 consumption and especially during chemical weathering of silicate minerals.

KEYWORDS

biomineralization, cyanobacteria, basaltic glass, carbonate, saturation index, critical zone

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