Determination of triple oxygen isotope composition in CO2 from various biogeochemical processes

A higher level of ¹⁷O isotope anomaly (defined as Δ¹⁷O=1000*ln(1+δ¹⁷O/1000)-0.525*1000*ln(1+δ¹⁸O/1000)) has been observed in the tropospheric CO₂ in the Taiwan region using a newly developed method of analysis. The Δ¹⁷O signal is somewhat larger than that previously estimated. In addition, there is a large variability in Δ¹⁷O. Several possibilities exist to explain the data. Apart from the interpretation of high flux of Δ¹⁷O from outside sources it is possible that the triple isotope signature of biological CO₂ sources could be different from that assumed so far. This would impact the derivation of Δ¹⁷O value. For example, the analysis assumes a coefficient of 0.525 in the tropospheric CO₂ but the CO₂ in near surface region can come from diverse sources with differing coefficients. If the true coefficient is higher than 0.525 we would obtain a higher Δ¹⁷O values than calculated with 0.525. Therefore, it is important to characterize the triple oxygen isotope of soil respired CO₂ for proper interpretation of high Δ¹⁷O of air CO₂ from Taiwan. Reference: Mahata S, Bhattacharya SK, Wang CH, Liang MC (2012) An improved CeO2 method for high precesion measurements of 17O/16O ratios for atmospheric carbon dioxide. Rapid Commun. Mass Spectrom 26,1019-1022