SREL Reprint #2936

Carbon isotope fractionation in synthetic magnesian calcite

Concepción Jimenez-Lopez1,2, Christopher S. Romanek2, and Emilia Caballero1

1Estacion Experimental del Zaidin, CSIC, Professor Albareda 1, 18008 Granada, Spain
2Savannah 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 103 ln αMg-Cl—HCO3(aq)-) 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 103 ln αMg-Cl—HCO3(aq)- 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 α could not be evaluated from these experiments.

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.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).