Long-term observation of mass-independent oxygen isotope anomaly in stratospheric CO sub(2)

• Published in: Atmospheric chemistry and physics 2008-01, Vol.8 (20), p.6189-6197
• Main Authors: Kawagucci, S, Tsunogai, U, Kudo, S, Nakagawa, F, Honda, H, Aoki, S, Nakazawa, T, Tsutsumi, M, Gamo, T
• Format: Article
• Language: English
• ISSN: 1680-7316; 1680-7324

Stratospheric and upper tropospheric air samples were collected during 1994-2004 over Sanriku, Japan and in 1997 over Kiruna, Sweden. Using these archived air samples, we determined the triple oxygen-isotope composition of stratospheric CO sub(2) and the N sub(2)O mixing ratio. The maximum Delta super(17)OCO sub(2) value of +12.2ppm, resembling that observed previously in the mesosphere at 60 km height, was found in the middle stratosphere over Kiruna at 25.6 km height, suggesting that upper stratospheric and mesospheric air descended to the middle stratosphere through strong downward advection. A least-squares regression analysis of our observations on a delta super(18)OCO sub(2)- delta super(17)OCO sub(2) plot (r super(2)>0.95) shows a slope of 1.63+/-pm0.10, which is similar to the reported value of 1.71+/- 0.06, thereby confirming the linearity of three isotope correlation with the slope of 1.6-1.7 in the mid-latitude lower and middle stratosphere. The slope decrease with increasing altitude and a curvy trend in three-isotope correlation reported from previous studies were not statistically significant. Using negative linear correlations of Delta super(17)OCO sub(2) and delta super(18)OCO sub(2) with the N sub(2)O mixing ratio, we quantified triple oxygen-isotope fluxes of CO sub(2) to the troposphere as +48ppm GtC/yr ( Delta super(17)OCO sub(2)) and +38ppm GtC/yr ( delta super(18)OCO sub(2)) with similar to 30% uncertainty. Comparing recent model results and observations, underestimation of the three isotope slope and the maximum Delta super(17)OCO sub(2) value in the model were clarified, suggesting a smaller O sub(2) photolysis contribution than that of the model. Simultaneous observations of delta super(18)OCO sub(2), delta super(17)OCO sub(2), and N sub(2)O mixing ratios can elucidate triple oxygen isotopes in CO sub(2) and clarify complex interactions among physical, chemical, and photochemical processes occurring in the middle atmosphere.