Abstract
The triple oxygen isotope signature Δ(17)O in atmospheric CO(2), also known as its "(17)O excess," has been proposed as a tracer for gross primary production (the gross uptake of CO(2) by vegetation through photosynthesis). We present the first global 3-D model simulations for Δ(17)O in atmospheric CO(2) together with a detailed model description and sensitivity analyses. In our 3-D model framework we include the stratospheric source of Δ(17)O in CO(2) and the surface sinks from vegetation, soils, ocean, biomass burning, and fossil fuel combustion. The effect of oxidation of atmospheric CO on Δ(17)O in CO(2) is also included in our model. We estimate that the global mean Δ(17)O (defined as Δ17O = ln(δ17O + 1) - λRL · ln(δ18O + 1) with λ (RL) = 0.5229) of CO(2) in the lowest 500 m of the atmosphere is 39.6 per meg, which is ∼20 per meg lower than estimates from existing box models. We compare our model results with a measured stratospheric Δ(17)O in CO(2) profile from Sodankylä (Finland), which shows good agreement. In addition, we compare our model results with tropospheric measurements of Δ(17)O in CO(2) from Göttingen (Germany) and Taipei (Taiwan), which shows some agreement but we also find substantial discrepancies that are subsequently discussed. Finally, we show model results for Zotino (Russia), Mauna Loa (United States), Manaus (Brazil), and South Pole, which we propose as possible locations for future measurements of Δ(17)O in tropospheric CO(2) that can help to further increase our understanding of the global budget of Δ(17)O in atmospheric CO(2).