Signal strength and climate calibration of a European tree-ring isotope network

We present the first European network of tree ring delta C-13 and delta O-18, containing 23 sites from Finland to Morocco. Common climate signals are found over broad climatic-ecological ranges. In temperate regions we find positive correlations with summer maximum temperatures and negative correlations with summer precipitation and Palmer Drought Severity Indices (PDSI) with no obvious speciesspecific differences. Regional delta C-13 and delta O-18 chronologies share high common variance in year-to-year variations. Long-term variations, however, exhibit differences that may reflect spatial variability in environmental forcings, age trends and/or plant physiological responses to increasing atmospheric CO2 concentration. Rotated principal component analysis (RPCA) and climate field correlations enable the identification of four sub-regions in the delta O-18 network - northern and eastern Central Europe, Scandinavia and the western Mediterranean. Regional patterns in the delta C-13 network are less clear and are timescale dependent. Our results indicate that future reconstruction efforts should concentrate on delta O-18 data in the identified European regions.