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Proc Natl Acad Sci U S A. 2013 Oct 29;110(44):17680-5. doi: 10.1073/pnas.1213082110. Epub 2013 Aug 12.

Unexpected variations in the triple oxygen isotope composition of stratospheric carbon dioxide.

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  • 1Departments of Chemistry and Earth and Planetary Science, University of California, Berkeley, CA 94720.

Abstract

We report observations of stratospheric CO2 that reveal surprisingly large anomalous enrichments in (17)O that vary systematically with latitude, altitude, and season. The triple isotope slopes reached 1.95 ± 0.05(1σ) in the middle stratosphere and 2.22 ± 0.07 in the Arctic vortex versus 1.71 ± 0.03 from previous observations and a remarkable factor of 4 larger than the mass-dependent value of 0.52. Kinetics modeling of laboratory measurements of photochemical ozone-CO2 isotope exchange demonstrates that non-mass-dependent isotope effects in ozone formation alone quantitatively account for the (17)O anomaly in CO2 in the laboratory, resolving long-standing discrepancies between models and laboratory measurements. Model sensitivities to hypothetical mass-dependent isotope effects in reactions involving O3, O((1)D), or CO2 and to an empirically derived temperature dependence of the anomalous kinetic isotope effects in ozone formation then provide a conceptual framework for understanding the differences in the isotopic composition and the triple isotope slopes between the laboratory and the stratosphere and between different regions of the stratosphere. This understanding in turn provides a firmer foundation for the diverse biogeochemical and paleoclimate applications of (17)O anomalies in tropospheric CO2, O2, mineral sulfates, and fossil bones and teeth, which all derive from stratospheric CO2.

PMID:
23940331
[PubMed - indexed for MEDLINE]
PMCID:
PMC3816447
Free PMC Article
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