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

• Published in: Atmospheric chemistry and physics discussions 2007-11, Vol.7 (6), p.15723-15737
• 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: 1680-7367; 1680-7375

Anomalous oxygen isotopic compositions of stratospheric CO sub(2) were first reported in 1989, although their detailed behavior in the middle atmosphere is still open question. We collected 60 stratospheric air samples over Sanriku, Japan from 1991 to 2004 and Kiruna, Sweden in 1997. Using these accumulated air samples, we performed long-term observations of triple oxygen isotope compositions of stratospheric CO sub(2). It is the first simultaneous observation in the stratosphere of both relations between Delta super(17)O sub(CO2) and [N sub(2)O], and delta super(18)O sub(CO2) and delta super(17)O sub(CO2), accurately. Observations confirmed simultaneous linear correlations between delta super(18)O sub(CO2), Delta super(17)O sub(CO2), and [N sub(2)O] within [N sub(2)O]>50 ppbv: the correlations faded away along with decreasing [N sub(2)O] from 50 ppbv. For dividing observation results by [N sub(2)O]=50 ppbv, the divided datasets show that 1) both Delta super(17)O sub(CO2) and delta super(18)O sub(CO2) are conservative parameters within the N sub(2)O-rich division, 2) the slope of least squares regression on delta super(18)O- delta super(17 )O plot for the N sub(2)O-rich division is significantly steeper than that of the N sub(2)O-depleted one, and 3) the N sub(2)O-depleted division shows a discrepancy with recent model calculations, suggesting unconsidered isotope fractionation processes on complicated oxygen interactions in the CO sub(2)-O sub(3)-O sub(2[ /subscript] system in the upper stratosphere and mesosphere.)