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 O-17 oxygen anomaly [Delta O-17 = 1000 x ln(1 + delta O-17/1000) - 0.516 x 1000 x ln(1 + delta O-18/1000)], with a value > 0.5 parts per thousand 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 parts per thousand. Therefore, any anomaly in near surface CO2 would reflect the balance between stratospheric input and exchange with the aforementioned surface sources. We have analyzed Delta O-17 values of CO2 separated from air samples collected in Taipei, Taiwan, located in the western Pacific region. The obtained mean anomaly is 0.42 +/- 0.14 parts per thousand (1-sigma standard deviation), in good agreement with model prediction and a published decadal record. Apart from typically used delta C-13 and delta O-18 values, the Delta O-17 value could provide an additional tracer for constraining the carbon cycle.