Near Surface CO2 Triple Oxygen Isotope Composition

The isotopic composition of carbon dioxide in the atmosphere is a powerful tool for constraining its sources and sinks. In particular, the ^(17)O oxygen anomaly [Δ^(17)O = 1000 × ln(1 + δ^(17)O/1000) - 0.516 × 1000 × ln(1 + δ^(18)O/1000)], with a value ＞ 0.5 per mille produced in the middle atmosphere, provides an ideal tool for probing the exchange of carbon dioxide between the biosphere/hydrosphere and atmosphere. The biosphere/hydrosphere and anthropogenic emissions give values ≤ 0.3 per mille. Therefore, any anomaly in near surface CO_2 would reflect the balance between stratospheric input and exchange with the aforementioned surface sources. We have analyzed Δ^(17)O values of CO_2 separated from air samples collected in Taipei, Taiwan, located in the western Pacific region. The obtained mean anomaly is 0.42 ± 0.14 per mille (1-σ standard deviation), in good agreement with model prediction and a published decadal record. Apart from typically used δ^(13)C and δ^(18)O values, the Δ^(17)O value could provide an additional tracer for constraining the carbon cycle.