Departments of Chemistry and Earth and Planetary Science, University of California, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2013 Oct 29;110(44):17680-5. doi: 10.1073/pnas.1213082110. Epub 2013 Aug 12.
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.
我们报告了平流层 CO2 的观测结果，这些结果显示（17）O 的异常富集非常大，且与纬度、海拔和季节有系统的变化。在中层平流层和北极涡旋中，三重同位素斜率达到 1.95 ± 0.05（1σ），而在前一次观测中为 1.71 ± 0.03，与先前的观测结果相比，显著增加了 0.52 的质量依赖值的 4 倍。对实验室测量的光化学臭氧-CO2 同位素交换的动力学建模表明，单独的非质量依赖同位素效应对臭氧形成的定量解释了实验室中 CO2 中的（17）O 异常，解决了模型与实验室测量之间长期存在的差异。然后，模型对涉及 O3、O((1)D)或 CO2 的假设质量依赖同位素效应以及臭氧形成中异常动力学同位素效应的经验依赖性温度的敏感性，为理解实验室和平流层之间以及平流层不同区域之间同位素组成和三重同位素斜率的差异提供了概念框架。这种理解又为大气 CO2、O2、矿物硫酸盐和化石骨骼和牙齿中（17）O 异常在生物地球化学和古气候中的各种应用提供了更坚实的基础，所有这些都源自平流层 CO2。
