Dependence of delta18O and delta D in precipitation on climate

Different kinds of comparisons of delta18O with temperature are discussed, mainly for European stations from the IAEA/WMO network. Anomalies (deviations from mean monthly values) of delta18O are significantly correlated to temperature anomalies, but this correlation explains only about 10-20% of the overall isotopic variability. According to the Rayleigh condensation model, delta18O and delta D directly depend on the degree of rainout f which is given by the ratio between the water vapour mixing ratios at the sampling station and in the vapour source region. The observed relation between delta D and f at Valentia, Stuttgart and Vienna, taking the Azores as representing the vapour source region, is in remarkably good agreement with the Rayleigh model. (author)