A Dual Inlet System for Laser Spectroscopy of Triple Oxygen Isotopes in Carbonate‐Derived and Air CO 2

Abstract

Abstract Analyzing the triple oxygen isotope (Δ′ 17 O) composition of carbonates and air CO 2 can provide valuable information about Earth system processes. However, accurately measuring the abundance of the rare 17 O‐bearing CO 2 isotopologue using isotope ratio mass spectrometry presents significant challenges. Consequently, alternative approaches, such as laser spectroscopy, have been developed. Here, we describe an adaptable dual inlet system for a tunable infrared laser direct absorption spectrometer (TILDAS) that maintains stable instrumental conditions for subsequent sample and reference measurements. We report ∆′ 17 O measurements on three types of samples: reference CO 2 , CO 2 derived from the acid digestion of carbonates, and air CO 2 . The external repeatability (±1 σ ) for reference‐sample‐reference bracketing measurements is generally better than ±10 ppm, close to the average internal error of ±6 ppm. Our results demonstrate that laser spectroscopy is a capable technique for measuring triple oxygen isotopes with the precision required to resolve variations in the ∆′ 17 O values of air CO 2 and to use the ∆′ 17 O of carbonates for paleothermometry.

Plain Language Summary Tunable infrared laser direct absorption spectroscopy (TILDAS) is a technique that determines isotopologue abundances by shining a laser through the analyzed gas and measuring the amount of light absorbed. Laser spectroscopy is emerging as a competitive alternative to the more common isotope ratio mass spectrometry due to its ability to provide rapid and precise measurements of rare isotope ratios directly on CO 2 gas. We present a cost‐effective dual inlet system for TILDAS to measure the triple oxygen isotope composition of carbonates and air CO 2 . Our setup maintains stable measurement conditions, for example, instrumental temperature, gas composition, pressure, and achieves external repeatability generally below ±10 ppm. Triple oxygen isotope measurements with such precision enable resolving variations in the 17 O‐anomaly of air CO 2 and using the ∆′ 17 O values of carbonates for paleoenvironmental applications.

Key Points An inlet system using inexpensive hardware and open‐source software was developed for tunable infrared laser absorption spectroscopy Spectroscopic measurements of ∆′ 17 O in CO 2 can be negatively influenced by variable temperatures, uneven CO 2 mixing, which were addressed The external standard deviation of repeated ∆′ 17 O measurements of CO 2 from carbonates and air was better than 10 ppm