A tree-ring proxy of summer temperature anomalies for northern Finland for the past 7500 yr was analyzed using Fourier spectrum and wavelet approaches. Multicentennial (250–450 yr) variability is present in the proxy record during most of the time range. This variability is suggested to reflect low-frequency variability in the North Atlantic Oscillation. Century-scale (90–130 yr) variation is another important feature of the tree-ring proxy data during the Holocene and may be attributed to Glessberg solar activity variations. In addition, an approximately 2000-yr quasi-period is found in this temperature proxy data, similar to the millennial-scale variability, present in many climate records from the North Atlantic region. The results point to the importance of multiple forcings underlying significant Holocene climatic fluctuations.
