Large-Scale Climate Signals Of A European Oxygen Isotope Network From Tree Rings

We investigate the climate signature of delta O-18 treering records from sites distributed all over Europe covering the last 400 years. An empirical orthogonal function (EOF) analysis reveals two distinct modes of variability on the basis of the existing delta O-18 tree-ring records. The first mode is associated with anomaly patterns projecting onto the El Nino-Southern Oscillation (ENSO) and reflects a multiseasonal climatic signal. The ENSO link is pronounced for the last 130 years, but it is found to be weak over the period from 1600 to 1850, suggesting that the relationship between ENSO and the European climate may not be stable over time. The second mode of delta O-18 variability, which captures a north-south dipole in the European delta O-18 tree-ring records, is related to a regional summer atmospheric circulation pattern, revealing a pronounced centre over the North Sea. Locally, the delta O-18 anomalies associated with this mode show the same (opposite) sign with temperature (precipitation). Based on the oxygen isotopic signature derived from tree rings, we argue that the prevailing large-scale atmospheric circulation patterns and the related teleconnections can be analysed beyond instrumental records.