High precision δ18O measurements of atmospheric dioxygen using optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS)

• Main Authors: Piel, Clément, Romanini, Daniele, Farradèche, Morgane, Chaillot, Justin, Paul, Clémence, Bienville, Nicolas, Lauwers, Thomas, Sauze, Joana, Jaulin, Kévin, Prié, Frédéric, Landais, Amaëlle
• Format: Text
• Language: English
• Published: 2024
• Subjects: ice core
• Online Access: https://doi.org/10.5194/amt-2024-14; https://amt.copernicus.org/preprints/amt-2024-14/

Atmospheric dioxygen concentration and isotopic composition are closely linked to the carbon cycle through anthropic CO 2 emissions and biological processes such as photosynthesis and respiration. Measurement of isotopic ratio of atmospheric dioxygen, trapped in ice core bubbles, bring information about past variation in the hydrological cycle at low latitudes, as well as past productivity. Currently, the interpretation of those variations could be drastically improved with a better ( i.e. quantitative) knowledge of the oxygen fractionation that occur during photosynthesis and respiration processes. This could be achieved, for example, during experiment using closed- biological chambers. In order to estimate the fractionation coefficient with a good precision, one of the principal limitations is the need of high frequency on-line measurements of δ 18 O of O 2 and O 2 concentration. To address this issue, we developed a new instrument, based on the OF-CEAS (Optical-Feedback Cavity-Enhanced Absorption Spectroscopy) technique, enabling high temporal resolution and continuous measurements of dioxygen concentration as well as δ 18 O of O 2 , both simultaneously. Minimum of Allan deviation occurred between 10 and 20 minutes while precision reached 0.002 % for O 2 concentration and 0.06 ‰ for δ 18 O of O 2 , which correspond to the optimal integration time and analytical precision before drift start degrading the measurements. While humidity did not affect much the measured values, O 2 concentration had an influence on δ 18 O of O 2 , which should hence be quantified. To ensure good quality of O 2 concentration and δ 18 O of O 2 measurements we eventually proposed to measure calibration standard every 20 minutes.