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Magnesium isotope fractionation during hydrous magnesiumcarbonate precipitation with and without cyanobacteria

Mavromatis, Vasileios; Pearce, Christopher R.; Shirokova, Liudmila S.; Bundeleva, Irina A.; Pokrovsky, Oleg S.; Benezeth, Pascale and Oelkers, Eric H. (2012). Magnesium isotope fractionation during hydrous magnesiumcarbonate precipitation with and without cyanobacteria. Geochimica et Cosmochimica Acta, 76 pp. 161–174.

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The hydrous magnesium carbonates, nesquehonite (MgCO3.3H2O) and dypingite (Mg5(CO3)4(OH)2.5(H2O)), were precipitated at 25 oC in batch reactors from aqueous solutions containing 0.05 M NaHCO3 and 0.025 M MgCl2 and in the presence and absence of live photosynthesizing Gloeocapsa sp. cyanobacteria. Experiments were performed under a variety of conditions; the reactive fluid/bacteria/mineral suspensions were continuously stirred, and/or air bubbled in most experiments, and exposed to various durations of light exposure. Bulk precipitation rates are not affected by the presence of bacteria although the solution pH and the degree of fluid supersaturation with respect to magnesium carbonates increase due to photosynthesis. Lighter Mg isotopes are preferentially incorporated into the precipitated solids in all experiments. Mg isotope fractionation between the mineral and fluid in the abiotic experiments is identical, within uncertainty, to that measured in cyanobacteria bearing experiments; measured δ26 ranges from -1.54‰ to -1.16‰ in all experiments. Mg isotope fractionation is also found to be independent of reactive solution pH and Mg, CO32-, and biomass concentrations. Taken together, these observations suggest that Gloeocapsa sp. cyanobacterium does not appreciably affect magnesium isotope fractionation between aqueous fluid and hydrous magnesium carbonates.

Item Type: Journal Article
Copyright Holders: 2011 Elsevier Ltd
ISSN: 0016-7037
Academic Unit/Department: Science > Environment, Earth and Ecosystems
Item ID: 30526
Depositing User: Chris Pearce
Date Deposited: 03 Jan 2012 14:05
Last Modified: 23 Feb 2016 21:36
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