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Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria

Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria
Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria
The hydrous magnesium carbonates, nesquehonite (MgCO3·3H2O) and dypingite (Mg5(CO3)4(OH)2·5(H2O)), were precipitated at 25 °C 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 ?26Mg 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
0016-7037
161-174
Mavromatis, Vasileios
b15603d0-512c-48f1-ab49-10b5294ab4df
Pearce, Christopher R.
3d683112-72dc-444f-ae06-da9c571d799a
Shirokova, Liudmila S.
ead3938a-da5f-4ad7-84cb-bdf26e5a4d71
Bundeleva, Irina A.
c45bc92a-f820-4787-8b6a-e78a47422afc
Pokrovsky, Oleg S.
29fe42af-c104-459c-9f47-4076999f9ce3
Benezeth, Pascale
e43270bc-82df-4c1d-af45-7ee17a2c1574
Oelkers, Eric H.
3cf51d71-be44-4bed-803e-3b240bdb147b
Mavromatis, Vasileios
b15603d0-512c-48f1-ab49-10b5294ab4df
Pearce, Christopher R.
3d683112-72dc-444f-ae06-da9c571d799a
Shirokova, Liudmila S.
ead3938a-da5f-4ad7-84cb-bdf26e5a4d71
Bundeleva, Irina A.
c45bc92a-f820-4787-8b6a-e78a47422afc
Pokrovsky, Oleg S.
29fe42af-c104-459c-9f47-4076999f9ce3
Benezeth, Pascale
e43270bc-82df-4c1d-af45-7ee17a2c1574
Oelkers, Eric H.
3cf51d71-be44-4bed-803e-3b240bdb147b

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 magnesium carbonate precipitation with and without cyanobacteria. Geochimica et Cosmochimica Acta, 76, 161-174. (doi:10.1016/j.gca.2011.10.019).

Record type: Article

Abstract

The hydrous magnesium carbonates, nesquehonite (MgCO3·3H2O) and dypingite (Mg5(CO3)4(OH)2·5(H2O)), were precipitated at 25 °C 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 ?26Mg 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

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Published date: January 2012
Organisations: Geochemistry

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Local EPrints ID: 342520
URI: http://eprints.soton.ac.uk/id/eprint/342520
ISSN: 0016-7037
PURE UUID: 59d1ac3a-5e0a-4e02-8841-19369e42bcfc

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Date deposited: 07 Sep 2012 13:26
Last modified: 16 Dec 2019 20:36

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