Carbon Dioxide Isotope Analyzer

• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: Funded in 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 570615253

Oxygen, carbon, and hydrogen are the main elements of the hydrosphere, biosphere, lithosphere, and important components of the atmosphere. By studying the isotopic ratios of these elements in various material groups, it is possible to reconstruct processes (e.g., photosynthesis), conditions (e.g., temperature), and material flows (e.g., sources and sinks) in the present-day environment as well as throughout Earth's history. A general challenge with stable isotopes lies in their one-dimensional scale. The interpretation of 2H/1H, 13C/12C, and 18O/16O ratios is often ambiguous, as different processes may overlap. For instance, paleo-temperatures are reconstructed from measured 18O/16O ratios in carbonates. This is feasible when the carbonate forms in near-equilibrium with seawater. However, for many carbonates, this approach does not work because kinetic isotope fractionation processes distort equilibrium fractionation. Diagenesis can also alter the reconstructed temperatures. On the one-dimensional 18O/16O scale, these overlapping processes can often only be identified indirectly (e.g., using 13C/12C) and sometimes not at all. With the proposed instruments, 17O/16O ratios can be measured with the highest precision, allowing the resolution of minute differences in purely mass-dependent fractionation processes. This second dimension of oxygen isotopes enables the identification, quantification, and correction of overlapping processes. Using conventional mass spectrometers, high-precision 17O/16O ratios can only be determined on O2 gas, because in CO or CO2 gas, isotopologues containing 13C and 17O comprise the same masses. Even with new high-resolution mass spectrometers, comparable precision to that achieved with O2 gas cannot be attained with CO2, even with extended measurement times. The quantitative conversion of CO2 to O2 is, however, technically challenging. The instruments requested here are not mass spectrometers. Instead, they are based on an optical measurement approach. Such spectroscopic analyses are suitable for the direct measurement of CO2 gas from standard sample preparation methods. The analysis gas is introduced into an optical cell, where isotopologues are excited by a laser. By measuring the isotope-specific absorption bands, the isotopic composition of the analysis gas can be determined within fractions of a second. Similar instruments for H2O are already widely used. Recently, a commercial manufacturer has also developed a comparable instrument for CO2that meets our precision requirements for 17O/16O. In Bochum, there is an opportunity to combine the novel triple-oxygen isotope systematics (expressed as Δ′17O) with the relatively new clumped isotope thermometry (Δ47). A peripheral device specifically designed for Δ47 analyses to prepare carbonates is also included in this proposal.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Kohlendioxid-Isotopen Analysator
• Instrumentation Group: 1520 Meßgeräte für Gase (O2, CO2)
• Applicant Institution: Ruhr-Universität Bochum
• Leader: Professor Dr. Daniel Herwartz