Significant changes of subseries-means in the Finnish tree-ring index of 7638 years, with comparisons to glaciological evidence from Greenland and Alps

This study applies the scanning t-test to the tree-ring chronology of Scots pine (Pinus sylvestris L.) from Finnish Lapland for 7638 years for detecting significant changes of subseries means. Analyses are done on multi-centennial scales and the results are demonstrated both as figures and tables. Firstly, the tree-ring data were processed to smooth the high frequency fluctuations by using an 81-year low-pass Gaussian filter following the Maximum Entropy Spectrum analysis, which revealed two significant periodicities on 80.3-87.7-year and 30.8-31.8-year scales. Secondly, the scanning t-test detected 20 change-points in the low-passed series of the tree-ring chronology. The 7638-year tree-ring chronology was partitioned into 21 episodes with comparatively high or low subseries-mean index. The episode durations range from 105 to 845 years. On longer temporal scales, a decreasing tree-ring trend (indicating palaeoclimatic cooling) appeared during the period from 4960BC to 2442BC, an increasing trend (indicating palaeoclimatic warming) occurred during years 2441BC to 449BC, then a roughly normal stage followed between 425BC and 1148AD. The last 850 years contain three episodes of obvious changes: the episode in 1149-1447AD in high index, the episode in 1448AD-1735AD as a low index, and the episode in 1736-2004AD showing back to high index again. Thirdly, all the detected 21 episodes were verified by comparing the results with the previously published studies and their interpretation. This verification was expanded to some works on the ice-core and glacier in the Greenland and the Alps respectively, in the regional view.