EGU22-626, updated on 26 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Triple oxygen isotope fractionation of carbonate during carbonate precipitation and acid digestion

Pallab Roy1, Amzad Laskar2, and Mao-Chang Liang1
Pallab Roy et al.
  • 1Institute of Earth Sciences, Academia Sinica, No. 128, Section 2, Academia Rd, Nangang District, Taipei City, 115, Taiwan
  • 2Physical Research Laboratory, Physical Research Laboratory, University Area, Ahmedabad, Gujarat 380009, India

Stable oxygen isotopic composition (δ18O) of CO2 produced from carbonates in natural archives is a useful proxy for paleo precipitation and paleo temperature reconstruction. However, there exist multiple factors controlling the δ18O values, the applications of the δ18O alone for paleoclimate studies are thus limited. Anomaly in 17O in carbonates, expressed by Δ′17O=1000*ln(δ17O/1000+1)-λ*1000*ln(δ18O/1000+1) is another proxy to independently constrain aspects of climatic variables such as precipitation source variation and kinetic effects during carbonate precipitation. However, to use 17O anomaly for such studies, the triple oxygen isotope fractionation exponent (θ= lnα17/lnα18) must be known precisely. Knowledge of this parameter is central to emerging applications of carbonate triple oxygen isotopes to paleoclimate and paleo-hydrology studies. Though a number of theoretical and experimental studies have been carried out in the last few years, there remains no consensus on 𝛳 value for carbonate-water system, likely due to kinetic isotope fractionation during precipitation.

Here, we measured Δ′17O in synthetic carbonates as well as in the water from which the carbonates are precipitated to check how reliable the Δ′17O value of the parent water can be reconstructed from the carbonates or carbonate-digested CO2. To determine θcarbonate_CO2-water for precipitated carbonates, we synthesized carbonates in the laboratory at temperatures ranging from 10 ⸰C to 66 ⸰C using passive/active CO2 degassing method. Triple oxygen isotope compositions of the water were determined using water-CO2 equilibration followed by CO2-O2 exchange method and of the carbonate (CO2 liberated by acid digestion) using CO2-O2 exchange method. We analyzed our isotope data for their possible kinetic isotope effect and determined the 𝛳carbonate_CO2-water value for precipitated carbonates. We find that most of our synthetic carbonate samples did not attain the equilibrium. The 𝛳carbonate_CO2-water increases as the disequilibrium effect increases. We determined the θcarbonate_CO2-water from the samples precipitating in equilibrium. Furthermore, we do not find any differences in the 𝛳carbonate_CO2-water value for carbonate precipitated in equilibrium at 25 ⸰C and 35 ⸰C. An important issue of using Δ′17O in carbonates is to resolve the 𝛳acid for acid digestion which is resolved in the present study. Additionally, we determined the temperature dependent variation in 𝛳acid and find no significant changes between 0 ⸰C and 70 ⸰C.

How to cite: Roy, P., Laskar, A., and Liang, M.-C.: Triple oxygen isotope fractionation of carbonate during carbonate precipitation and acid digestion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-626,, 2022.


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