Oxygen isotope fractionation and equilibration kinetics between CO@d2 and H@d2O as a function of salinity of aqueous solutions

• Published in: Chemical geology Vol. 264; no. 1-4; pp. 122 - 126
• Main Authors: Lecuyer, C, Gardien, V, Rigaudier, T, Fourel, F, Martineau, F, Cros, A
• Format: Journal Article
• Language: English
• Published: 30.06.2009
• ISSN: 0009-2541
• DOI: 10.1016/j.chemgeo.2009.02.017

Oxygen isotope fractionation and equilibration kinetics between CO@d2 and H@d2O have been investigated at 313 K for salinities (S) ranging from 0 to 250 g L@u-@u1. In this range of salinity, times needed to reach oxygen isotope equilibrium between CO@d2 and H@d2O increase from 4 h to 12 h. Isotopic exchanges are comparable for KCl and NaCl-like (sea salt) solutions and are described by first-order kinetic reactions with ln(k)=-8.1485(+ /-0.0057)-0.00474(+/-3.87x10@u-@u5)S. The oxygen isotope fractionation factor between CO@d2 and H@d2O increases with salinity for both sea salt and KCl solutions with concentrations ranging from 0 to 250 g L@u-@u1 according to the following equation: 1000 ln(a@dC@dO@d2@d-@dH@d2@dO)sea salt=37.02(+ /-5x10@u-@u3)+3.96x10@u-@u3(+/-1.1x10@u-@u4)S-6.38x10@u-@u6(+ /-4.5x10@u-@u7)S@u2 (R@u2=0.998). The oxygen isotope analysis of seawater samples with a salinity of 35 g L@u-@u1 requires minor corrections of -0.15%% (V-SMOW). However, oxygen isotope ratios are overestimated by 0.4%% to 0.6%% in the case of highly saline natural waters (100 < S < 250 g L@u-@u1). Corrections of the oxygen isotope ratios due to changes in the salinity-dependent fractionation factors between CO@d2 and H@d2O must be taken into account during the study of waters sampled from salt marshes, hypersaline lakes and lagoons, or hydrothermal brines.