Triple oxygen isotope fractionation between CaCO3 and H2O in inorganically precipitated calcite and aragonite
Voarintsoa, N.R.G.; Barkan, E.; Bergel, S.; Vieten, R.; Affek, H.P. (2020). Triple oxygen isotope fractionation between CaCO3 and H2O in inorganically precipitated calcite and aragonite. Chem. Geol. 539: 119500. https://hdl.handle.net/10.1016/j.chemgeo.2020.119500 In: Chemical Geology. Elsevier: New York; London; Amsterdam. ISSN 0009-2541; e-ISSN 1872-6836, more |  |
| Author keywords | Triple oxygen isotope fractionation; Calcite-Aragonite; O-17(excess); Paleo-hydrology proxy |
| Authors | | Top | - Voarintsoa, N.R.G., more
- Barkan, E.
- Bergel, S.
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| Abstract | Carbonate bearing materials, such as foraminifera, mollusks shells, or speleothems, have the potential to preserve geochemical and isotopic signatures reflecting the environmental conditions at the time they formed. Beyond the conventional δ18O, information from triple oxygen isotopes (reported as 17Oexcess, which is defined as (ln (δ17O/1000 + 1) − λref ln (δ18O/1000 + 1)) × 106) in these archives promises to be a valuable tool to reconstruct past hydrological processes. The goal of this study is to determine the triple oxygen isotope fractionation between CaCO3 and H2O under well-constrained laboratory conditions. We performed laboratory experiments to precipitate CaCO3 polymorphs, either calcite or aragonite, at temperatures between 10 and 35 °C. We then evaluated the effect of polymorphism, temperature, and solution concentration on the 17Oexcess of CO2 extracted from these carbonates and the 17O isotopic fractionation (17α) between water and CaCO3. The obtained values of 18α and 17α between CO2 extracted from CaCO3 and parent water allow us to calculate the fractionation slope θ (=ln17α/ln18α). Our observations suggest that θ is indistinguishable at temperatures of 10 and 27 °C, but is slightly lower at 35 °C. The lower value at 35 °C may be related to disequilibrium during these experiments. We found that θ is independent of polymorph and of solution concentration, indicating that 17Oexcess is less sensitive than δ18O to these geochemical parameters and can thus be a robust proxy for reconstructing 17Oexcess of parent water. |
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