Triple oxygen isotope measurements of air CO2 around Göttingen

The triple oxygen isotope composition (δ¹⁸O and ∆’¹⁷O) of atmospheric CO₂ provides valuable information about CO₂ sources and carbon exchange fluxes between atmospheric reservoirs [1-2]. For example, stratospheric CO₂ has a large positive ¹⁷O-anomaly due to photochemical processes. The ∆’¹⁷O of tropospheric CO₂ is primarily influenced by carbonic anhydrase-catalyzed oxygen isotope exchange between air CO₂ and water in vegetation, resulting in an air CO₂ ∆’¹⁷O mainly governed by the isotope composition of local meteoric water. Additionally, CO₂ from fossil fuel combustion processes shows a negative ¹⁷O-anomaly inherited from the isotope composition of atmospheric O₂ [3].

Starting in April 2023, we conducted automated triple oxygen isotope measurements of air CO₂ in Göttingen using tunable infrared laser direct absorption spectroscopy (TILDAS; Aerodyne, USA) coupled with a custom-built inlet system. The internal error of the ∆’¹⁷O measurements was < 10 ppm and of the δ¹⁸Omeasurements < 0.01‰.

In this report, we present our initial results and discuss the contribution of various reservoirs to the ∆’¹⁷O of atmospheric CO₂ in Göttingen. We also examine daily and seasonal variations observed in our data.

[1] G. Koren et al., J. Geophys. Res. Atmos. 124, 8808–8836 (2019).

[2]  M. E. G. Hofmann et al., Geochim. Cosmochim. Acta. 199, 143–163 (2017).

[3]  B. Horváth, M. E. G. Hofmann, A. Pack, Geochim. Cosmochim. Acta. 95, 160–168 (2012).