Carbon isotope fractionation in synthetic magnesian calcite
Concepción Jimenez-Lopez,a, b, * Christopher
S. Romanekb and Emilia Caballeroa
aEstacion
Experimental del Zaidin, CSIC, Professor Albareda 1, 18008 Granada,
Spain
bSavannah River Ecology Laboratory and Department of Geology,
University of Georgia, Drawer E, Aiken SC 29802, USA
Abstract
Mg-calcite was precipitated at 25 °C in closed system, free-drift
experiments, from solutions containing NaHCO3, CaCl2
and MgCl2. The carbon stable isotope composition of bulk
solid and solution were analyzed from subsamples collected during
time course experiments of 24 h duration. Considering only the Mg-content
and d13C values for the bulk solid, the carbon isotope
fractionation factor for the Mg-calcite–HCO3(aq)-
system (as
) increased
with average mol percentage of Mg (XMg) in the solid at
a rate of (0.024 ± 0.011) per mol% MgCO3. Extrapolation
of this relationship to the pure calcite end member yields a value
of 0.82 ± 0.09, which is similar to published values for the
calcite–HCO3(aq)- system. Although did
not vary for precipitation rates that ranged from 103.21
to 104.60 µmol m-2 h-1, it
was not possible to hold Mg-content of the solid constant, so kinetic
effect on 103 ln a could not be evaluated from these experiments.
Correspondence
*Corresponding author. Present address: Departamento de Microbiologia,
Facultad de Ciencias, Universidad de Granada, Campus de Fuentenueva s/n,
18071 Granada, Spain. Fax: +34 958 249486.
E-mail address: cjl@ugr.es (C. Jimenez-Lopez).
SREL Reprint #2936
Concepción, J.-L., C. S. Romanek and E. Caballero. 2006. Carbon isotope fractionation in synthetic magnesian calcite. Geochimica et Cosmochimica Acta 70:1163-1171.
