Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published June 21, 2008 | Published
Journal Article Open

Seasonal cycle of C16O16O, C16O17O, and C16O18O in the middle atmosphere: Implications for mesospheric dynamics and biogeochemical sources and sinks of CO2


The isotopic anomaly of oxygen in atmospheric CO2 is caused by exchange reactions with isotopically anomalous O(1D) in the middle atmosphere. In the stratosphere, the major source of O(1D) is O3 photolysis; O3 is known to possess mass-independent isotopic composition, with δ 49O3 ≈ δ 50O3 ≈ 100‰ relative to atmospheric O2. Higher in the mesosphere, Lyman α-driven photodissociation of O2 provides a more important source of heavy O(1D) than O3 photolysis. Here we present a two-dimensional simulation of the isotopic composition of CO2 from the surface to an altitude of ∼130 km that adequately reproduce the observed seasonal cycle of CO2 in the upper troposphere and the age of air in the stratosphere. Our model results suggest that stratospheric-tropospheric exchange not only modifies the level of heavy CO2 in the troposphere, but also influences its seasonal cycle. Thus the isotopic composition of CO2 in the troposphere/biosphere could be affected by the downwelling air from the stratosphere. The predicted size of the effect is detectable by current instrumentation. Implications for the use of the isotopic composition of CO2 to constrain the gross carbon flux between the atmosphere and terrestrial biosphere and the dynamics in the remote mesosphere are discussed.

Additional Information

© 2008. American Geophysical Union. Received 3 January 2007; accepted 17 December 2008; published 21 June 2008. This work was supported in part by an NSC grant 96-2628-M-001-018 to the Academia Sinica and an NSF grant ATM-0529268 to the California Institute of Technology. Special thanks are due Xun Jiang and Run-Lie Shia for assisting in the construction of stream functions needed for the 2-D models for invaluable discussions and John Eiler for pointing out the reference describing the CO2-water isotopic exchange in firn.

Attached Files

Published - LIAjgrd08.pdf


Files (4.0 MB)
Name Size Download all
4.0 MB Preview Download

Additional details

September 14, 2023
October 23, 2023