Marko Scholze

Remarks on the Use of 13C and 18O isotopes in Atmospheric CO2 to Quantify Biospheric Carbon Fluxes

This chapter uses the mass-conservation equations for CO 2 and its isotopomers 13 CO 2 and CO 18 O that can be used to infer globally biospheric and oceanic net fluxes in the case of 18 C, and gross terrestrial biospheric fluxes in the case of 18 O. The quantitative use of atmospheric measurements of 13 C and 18 O in CO 2 to better constrain those fluxes requires knowledge of various processes specific to each isotopomer. The chapter is divided into two parts, one on each isotope. For 13 C, it reviews existing work that calculated isofluxes either using global estimates or derived isofluxes from spatially and temporally explicit models. In addition, it estimates the magnitude of new isofluxes that were not addressed in former studies. These cover the effects of biomass burning, rock weathering and volcanism, and the oxidation of reduced carbon gases into CO 2 within the atmosphere.