Global 3-D Simulations of the Triple Oxygen Isotope Signature Δ 17 O in Atmospheric CO 2

Abstract

The triple oxygen isotope signature ￎﾔ17O in atmospheric CO2, also known as its ￢ﾀﾜ17O excess,￢ﾀﾝ has been proposed as a tracer for gross primary production (the gross uptake of CO2 by vegetation through photosynthesis). We present the first global 3￢ﾀﾐD model simulations for ￎﾔ17O in atmospheric CO2 together with a detailed model description and sensitivity analyses. In our 3￢ﾀﾐD model framework we include the stratospheric source of ￎﾔ17O in CO2 and the surface sinks from vegetation, soils, ocean, biomass burning, and fossil fuel combustion. The effect of oxidation of atmospheric CO on ￎﾔ17O in CO2 is also included in our model. We estimate that the global mean ￎﾔ17O (defined as with ￎﾻRL = 0.5229) of CO2 in the lowest 500ￂﾠm of the atmosphere is 39.6ￂﾠper meg, which is ￢ﾈﾼ20ￂﾠper meg lower than estimates from existing box models. We compare our model results with a measured stratospheric ￎﾔ17O in CO2 profile from Sodankylￃﾤ (Finland), which shows good agreement. In addition, we compare our model results with tropospheric measurements of ￎﾔ17O in CO2 from Gￃﾶttingen (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 ￎﾔ17O in tropospheric CO2 that can help to further increase our understanding of the global budget of ￎﾔ17O in atmospheric CO2.