Deutsche Übersetzung des Titels: Sauerstoffisotope als Indikator für biosphärische CO2 Bruttoflüsse : eine lokale Machbarkeitsstudie

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Übersetzung des Abstracts (Englisch)

Quantitative knowledge of gross biospheric CO2 fluxes is crucial in atmospheric carbon cycle budgeting, especially in view of unknown biospheric feedback mechanisms to an increasing atmospheric CO2 mixing ratio or to temperature changes. The 18O/16O ratio of CO2 has the potential to separate respiration and assimilation fluxes because of their characteristic isotopic signatures derived from equilibration with respective water reservoirs (i.e. soil and leaf water). The associated processes were investigated here on a local scale during three intensive measurement campaigns in a natural boreal forest reserve in Russia. Diurnal cycles of atmospheric CO2 and its stable isotope ratios, of the 18O/16O ratio of atmospheric water vapour, leaf and soil water were measured. The data sets were then quantitatively interpreted in a 222Radon-transport-calibrated 1-D canopy box model. On the basis of observations and plant physiological parameterisations, for the first time, the feasibility to separate gross ecosystem CO2 fluxes could be demonstrated. Reasonable agreement with classical local scale methods could be achieved, whereby the model results are most sensitive to the parameterisation of leaf internal CO2 gradients. Concurrent year-round aircraft CO2 and stable isotope observations showed that the biospheric ecosystem 18O signals are effectively transferred into the free troposphere. Provided that adequate parameterisations on the leaf scale can be achieved, this gives the perspective to successfully use the 18O/16O ratio in atmospheric CO2 within coupled mesoscale or even global biosphere-atmosphere models of the carbon cycle.