Triple oxygen isotope fractionation between CaCO3 and H2O in inorganically precipitated calcite and aragonite
Introduction
Calcium carbonate is well-known to have the potential to preserve various geochemical signals, reflecting the environmental conditions at the time in which the carbonate mineral formed. Since the pioneering works of Urey (1947) and Emiliani (1966), the isotopic composition, specifically δ18O, of marine and terrestrial carbonates has been used as a paleoclimate proxy that records a combination of temperature and water isotopic composition. Additional carbonate-based proxies, such as Mg/Ca and clumped isotopes, are often used as geochemical thermometers (e.g., Eiler, 2011; Elderfield et al., 2006), complementing information from δ18O. In terrestrial carbonates, such as speleothems, δ18O is interpreted as a recorder of the weighted mean rainfall δ18O, often reflecting the amount of rainfall in low latitude records (e.g., McDermott, 2004). This, however, does not capture the full hydrological complexity, such as the variability in moisture sources and the effect of local evaporation (although a few studies were able to link speleothem δ18O changes with changes in moisture sources during specific time intervals in the past, such as the 8.2 ka event; e.g., Dominguez-Villar et al., 2009; Voarintsoa et al., 2019). These gaps can be filled by information from 17Oexcess in water that may be archived in a variety of carbonates.
The parameter 17Oexcess is expressed as (ln(δ17O/1000 + 1) − λref ln(δ18O/1000 + 1)) × 106, or simply (δ′17O − λref × δ′18O) × 103, and is reported in per meg (e.g., Barkan and Luz, 2012; Luz and Barkan, 2010). The slope λref is a mass dependent reference, with the value 0.528 used in water, CO2, and CaCO3.
Meteoric water 17Oexcess is largely dependent on the atmospheric conditions, such as relative humidity, in the region where water vapor form (e.g., Angert et al., 2004; Luz and Barkan, 2010). However, there are indications for the influence of additional processes during precipitation, associated with local conditions. The 17Oexcess data of Li et al. (2015) from U.S tap waters suggest a potential influence of mixing of moisture sources and re-evaporation during precipitation. In high latitude regions, 17Oexcess is mainly influenced by kinetic processes related to super-saturation during vapor condensation at cold climate (e.g. Landais et al., 2012; Schoenemann et al., 2014). In mid to low latitude regions, 17Oexcess is mainly affected by evaporation of rain droplets, especially during warm climatic conditions (Landais et al., 2010; Risi et al., 2013; Li et al., 2015; Passey and Ji, 2019).
Whereas fossil water 17Oexcess can be obtained from ice cores, fluid inclusions, or gypsum hydration water (Affolter et al., 2015; Gázquez et al., 2018; Landais et al., 2008), these archives are limited in their geographic distribution. A broader coverage can be obtained by measuring 17Oexcess in carbonates. Recent analytical developments (Passey et al., 2014; Barkan et al., 2015; Mahata et al., 2016) enable high precisions measurements of 17Oexcess in CO2 released from CaCO3, which in turn may serve as a recorder of 17Oexcess of the water in which the mineral grows (Passey et al., 2014; Levin et al., 2014; Passey and Ji, 2019). Despite the recent advancement in measuring triple oxygen isotopes in carbonate materials, the fractionation involved in this proxy has not yet been characterized by laboratory experiments, to provide a framework necessary to quantitatively interpret past records. Here, we examine the triple oxygen isotope fractionation in the CaCO3–H2O system focusing on the effect of mineralogy, using laboratory precipitation experiments of calcite, aragonite, and their mixtures at temperatures of 10, 27, and 35 °C. We also examine the role of initial solution concentrations, as a simple way to assess the role of dissolved inorganic carbon (DIC) concentration on the triple oxygen isotope fractionation. The data allows us to calculate the fractionation slope, θ (=ln17α/ln18α), in order to interpret 17Oexcess in natural carbonates as a geochemical archive for paleo-hydrological processes.
Section snippets
Precipitation experiment
Precipitation experiments were performed by mixing solutions containing NaHCO3 (Baker Analyzed Reagent, J.T. Baker ref. 1-3506) and CaCl2·2H2O (Sigma-Aldrich CAS no. 10035-04-8) to reach an initial DIC concentration of 25 mM (at 10, 27, and 35 °C) and 5 mM (at 27 °C, to test the effect of initial DIC). MgCl2·6H2O (Sigma Aldrich CAS no. 7791-18-6) was added to obtain a total Mg-Ca concentration of 25 mM or 5 mM, respectively. The Mg:Ca ratio for either the 5 mM or 25 mM solution was defined
Results
The results from this study are presented in Fig. 1, Fig. 2, Fig. 3, Fig. 4, and details are given in Table 1, Table 2, Table 3.
Mineralogy and molarity
Calcite and aragonite are two common carbonate minerals that are used in paleoclimate and paleo-environment reconstruction (e.g., in speleothems, foraminifera, mollusk shells, and lake deposits). Often, calcite and aragonite co-occur in one sample (e.g., in speleothems; Holmgren et al., 2003; Voarintsoa et al., 2017). In such cases, the difference in 18α between the two polymorphs (Kim et al., 2007b) has to be accounted for in the aragonite δ18O to conform with the calcite values and to avoid
Conclusions
Results from this experimental study allow us to determine the triple oxygen isotope fractionations in the CaCO3–H2O system. We found that the fractionation slope θCaCO3–H2O is: (1) polymorph independent, i.e., we observe no significant difference between calcite, aragonite, and their mixture; (2) indistinguishable at temperatures of 10 and 27 °C but possibly slightly lower at 35 °C (the lower value may be associated with kinetic effects related to the fast precipitation observed in these
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was supported by ERC (Grant SPADE-724097) to HPA. NRGV is currently supported by the EU-HORIZON Marie SkŁodowska Curie Fellowship H2020-MSCA-IF-2017 no. 796707. We thank the editor and two anonymous reviewers for helpful comments.
References (60)
- et al.
Triple isotope (δD, δ17O, δ18O) study on precipitation, drip water and speleothem fluid inclusions for a Western Central European cave (NW Switzerland)
Quat. Sci. Rev.
(2015) - et al.
Kinetic 17O effects in the hydrological cycle: indirect evidence and implications
Geochim. Cosmochim. Acta
(2004) - et al.
Experimental studies of oxygen isotope fractionation in the carbonic acid system at 15°, 25°, and 40 °C
Geochim. Cosmochim. Acta
(2005) - et al.
Oxygen isotope fractionation in marine aragonite of coralline sponges
Geochim. Cosmochim. Acta
(2000) - et al.
Equilibrium mass-dependent fractionation relationships for triple oxygen isotopes
Geochim. Cosmochim. Acta
(2011) Paleoclimate reconstruction using carbonate clumped isotope thermometry
Quat. Sci. Rev.
(2011)- et al.
Calibrations for benthic foraminiferal Mg/Ca paleothermometry and the carbonate ion hypothesis
Earth Planet. Sci. Lett.
(2006) - et al.
Variations of 18O content of water from natural sources
Geochim. Cosmochim. Acta
(1953) - et al.
Oxygen isotope fractionation between calcite and fluid as a function of growth rate and temperature: an in situ study
Chem. Geol.
(2012) - et al.
Triple oxygen and hydrogen isotopes of gypsum hydration water for quantitative paleo-humidity reconstruction
Earth Planet. Sci. Lett.
(2018)
Oxygen and carbon isotope fractionation in biogenic aragonite–temperature effects
Chem. Geol.
Triple oxygen isotope fractionation in the DIC-H2O-CO2 system: a numerical framework and its implications
Geochim. Cosmochim. Acta
Isotopic fractionations associated with phosphoric acid digestion of carbonate minerals: insights from first-principles theoretical modeling and clumped isotope measurements
Geochim. Cosmochim. Acta
Theoretical calibration of the triple oxygen isotope thermometer
Geochim. Cosmochim. Acta
Persistent millennial-scale climatic variability over the past 25,000 years in Southern Africa
Quat. Sci. Rev.
Equilibrium and nonequilibrium oxygen isotope effects in synthetic carbonates
Geochim. Cosmochim. Acta
Phosphoric acid fractionation factors for calcite and aragonite between 25 and 75 °C: revisited
Chem. Geol.
Oxygen isotope fractionation between synthetic aragonite and water: influence of temperature and Mg2+ concentration
Geochim. Cosmochim. Acta
Normalization of stable isotope data for carbonate minerals: Implementation of IUPAC guidelines
Geochim. Cosmochim. Acta
Combined measurements of 17Oexcess and d-excess in African monsoon precipitation: implications for evaluating convective parameterizations
Earth Planet. Sci. Lett.
Triple oxygen isotope variations in sedimentary rocks
Geochim. Cosmochim. Acta
Continental scale variation in 17Oexcess of meteoric waters in the United States
Geochim. Cosmochim. Acta
Variations of 17O/16O and 18O/16O in meteoric waters
Geochim. Cosmochim. Acta
Palaeo-climate reconstruction from stable isotope variations in speleothems: a review
Quat. Sci. Rev.
Response of a modern cave system to large seasonal precipitation variability
Geochim. Cosmochim. Acta
Triple oxygen isotopes in biogenic and sedimentary carbonates
Geochim. Cosmochim. Acta
Triple oxygen isotope signatures of evaporation in lake waters and carbonates: a case study from the western United States
Earth Planet Sc Lett
Effect of polymorphism and magnesium substitution on oxygen isotope fractionation between calcium carbonate and water
Geochim. Cosmochim. Acta
Factors determining δ13C and δ18O fractionation in aragonitic otoliths of marine fish
Geochim. Cosmochim. Acta
Investigating the 8.2 ka event in northwestern Madagascar: Insight from data–model comparisons
Quat. Sci. Rev.
Cited by (0)
- 1
Current address: Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Leuven, Belgium.