Open AccessExperimental Constraints on Clumped Isotope Fractionation During BaCO 3 Precipitation
Author(s) -
Guo Yangrui,
Deng Wenfeng,
Wei Gangjian
Publication year - 2022
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2021gc010249
Subject(s) - carbonate , equilibrium fractionation , isotope fractionation , fractionation , disequilibrium , geology , isotopes of carbon , precipitation , oxygen isotope ratio cycle , stable isotope ratio , isotopes of oxygen , isotope , mineralogy , geochemistry , chemistry , environmental chemistry , total organic carbon , medicine , physics , organic chemistry , quantum mechanics , meteorology , ophthalmology
Reliable temperature reconstruction by carbonate clumped isotope (Δ 47 ) thermometry requires isotopic equilibrium during carbonate growth. However, many carbonate minerals grow at high rates and exhibit disequilibrium isotopic states. Carbonate Δ 47 disequilibrium arising from kinetic isotope effects (KIEs) specific to carbonate growth still remains unclear, and requires experimental constraints. Here we present a series of rapid witherite (BaCO 3 ) precipitation experiments intended to constrain bulk carbon, oxygen and clumped isotopic fractionation during unidirectional precipitation of BaCO 3 from dissolved inorganic carbon solutions under various pH and temperature conditions. We found that rapid BaCO 3 growth can lead to lower δ 13 C, δ 18 O, and Δ 47 values in HCO 3 − ‐dominated solutions, especially at low temperatures. Our experiments provide constraints on kinetic fractionation factors (KFFs) associated with the rapid carbonate growth and their temperature dependence. KFFs for δ 13 C and δ 18 O are broadly consistent with previous experimental estimates, although the Δ 47 KFF for BaCO 3 precipitation from HCO 3 − ‐dominated solution is not consistent with an earlier theoretical estimate, necessitating a re‐evaluation of the current model of the KIE associated with carbonate growth. Our results clearly verify a preference for the CO 3 2− pathway during carbonate precipitation, with important implications for new isotope fractionation models for natural carbonates. The fractionation relationship between Δ 47 and δ 18 O found in this study allows more precise identification of KIEs associated with rapid carbonate growth.