Annual oak (Quercus robur L.) latewood Δ13C values are presented for the period 1895--1994 for two sites with different hydrological characteristics in southwest Finland. No appreciable anthropogenic 13C depletion was observed in the time-series. Δ13C indices record high-frequency common forcing better than lower-frequency forcing. High-frequency fluctuations in the Δ13C indices are highly correlated with climatic variables. Cross correlation analysis of tree ring Δ13C indices and climate variables show that there is no significant difference (p<0.01) in the climate response of tree ring Δ13C indices between the two sites. This work demonstrates that significant climate signals are contained in isotopic measurements of trees whose ring-widths contain little or no such information.¿ 1997 American Geophysical Union