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| Titel |
The evolution of Carbon isotopes in calcite in the presence of cyanobacteria |
| VerfasserIn |
Christian Grimm, Vasileios Mavromatis, Oleg S. Pokrovsky, Eric H. Oelkers |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128499
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| Publikation (Nr.) |
 EGU/EGU2016-8492.pdf |
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| Zusammenfassung |
| Stable isotopic compositions in carbonates are widely used as indicators of environmental
conditions prevailing during mineral formation. This reconstruction is substantially based on
the assumption that there is no change in the mineral composition over geological
time.
However, recent experimental studies have shown that carbon and magnesium isotopes in
hydrous Mg-carbonates undergo continuous re-equilibration with the ambient solution even
after mineral precipitation stopped ([1] and [2], respectively).
To verify whether this holds true for anhydrous Ca-bearing carbonates which readily form
at earth’s surface environments, a series of batch system calcite precipitation experiments
were performed in the presence of actively growing cyanobacteria Synechococcus sp. The
bacteria were grown at ambient temperature in a BG11 culture medium (SIGMA C3061) and
continuous stirring, air-bubbling and illumination. Calcite precipitation was initiated
by the addition of 8.5mM CaCl2 and 0–50 mM NaHCO3 or NaHCO3-Na2CO3
mixtures.
The presence of cyanobacteria is on one hand promoting CaCO3 formation due to
increasing pH resulting from photosynthesis. On the other hand, actively growing
cyanobacteria drastically change carbon isotope signature of the aqueous fluid phase by
preferably incorporating the lighter 12C isotope into biomass [1].
This study explores the effect of continuously changing carbon isotope compositions in
dissolved inorganic carbon (DIC) on precipitated calcite which is in chemical equilibrium
with the ambient fluid phase.
[1] Mavromatis et al. (2015). The continuous re-equilibration of carbon isotope
compositions of hydrous Mg-carbonates in the presence of cyanobacteria. Chem. Geol. 404,
41-51
[2] Mavromatis et al. (2012). Magnesium isotope fractionation during hydrous
magnesium carbonate precipitation with and without cyanobacteria. Geochim. Cosmochim.
Acta 76, 161-174 |
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