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The response of the ¹⁸O/¹⁶O composition of atmospheric CO₂ to changes in environmental conditions

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  • This study investigates the response of the global mean and spatial variations of the δ¹⁸O value of atmospheric CO₂ (δCₐ) to changes in soil CO₂ hydration rates, relative humidity, the δ¹⁸O value of precipitation and water vapor, visible radiation, temperature, and ecosystem flux partitioning. A three-dimensional global transport model was coupled to a mechanistic land surfacemodel and was used to calculate isotopic fluxes of CO₂ and H2Oand the resulting δCₐ. The model reproduced the observed global mean and north-south gradient in δCₐ. The simulated seasonal amplitude and phases of CO₂ and δCₐ agreed well at some but not all locations. Sensitivity tests with relative humidity increased by 3.2% from its original value decreased δCₐ by 0.21‰. Similarly, a global 3.3‰ decrease in the isotopic composition of both precipitation and water vapor (δWP and δWₐᵥ, respectively) caused a 2.6‰decrease in δCₐ. A 1 K increase in atmospheric temperatures also affected δCₐ, but there was a very small δCₐ response to realistic changes in light levels. Experiments where leaf and soil CO₂ fluxes were repartitioned revealed a nontrivial change to δCₐ. The predicted north-south δCₐ gradient increased in response to an increase in soil CO₂ hydration rates. However, the δCₐ gradient also had a large response to global changes in δWₚ and δWₐᵥ. This result is particularly important since most models fail to deplete δWₚ enough at middle and high latitudes, where the influence of δWₚ and δWₐᵥ on the δCₐ gradient is strongest.
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  • Buenning, N., D. Noone, J. Randerson, W. J. Riley, and C. Still (2014), The response of the ¹⁸O/¹⁶O composition of atmospheric CO₂ to changes in environmental conditions. Journal of Geophysical Research: Biogeosciences, 119, 55–79. doi:10.1002/2013JG002312
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  • 119
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  • 1
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  • Office of Science, Office of Biological and Environmental Research, Climate and Environmental Science Division, of the U.S. Department of Energy under contract DEAC02-05CH11231 to Berkeley Lab, NOAA Climate Program Office (award NA03OAR4310059)
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