Observations of the anomalous oxygen isotopic composition of carbon dioxide in the lower stratosphere and the flux of the anomaly to the troposphere

Measurements of the triple oxygen isotopic composition of stratospheric CO2 in whole air samples from the NASA ER-2 aircraft show anomalous enrichments in O-17 and O-18. The compact correlation of the isotope anomaly (defined as Delta(17)O = delta(17)O - 0.516 x delta(18)O) with simultaneous N2O measurements demonstrates that Delta(17)O(CO2) is a long-lived tracer with a stratospheric source. These characteristics, and an isotopic link to O-3 production, make Delta(17)O(CO2) potentially useful as a tracer of integrated stratospheric chemistry and transport. The Delta(17)O(CO2):N2O correlation is also used to estimate a net Delta(17)O(CO2) flux to the troposphere of 3.6 +/- 0.9 x 10(15)parts per thousand mol CO2 yr(-1). This flux is required to predict and understand the CO2 and O-2 isotope anomalies in the troposphere and their use as tracers of gross carbon exchanges between the atmosphere and biosphere on interannual to glacial-interglacial time scales.