HOLOCENE CLIMATIC VARIATIONS IN SOUTHERN FINLAND RECONSTRUCTED FROM PEAT-INITIATION DATA

Radiocarbon and pollen analytical dates of 71 basal-peat samples from 23 sites in the Boreal region of southern Finland were used to reconstruct patterns of peat initiation and the subsequent spread of peat during the Holocene. Only mires known for certain as having originated through paludification were considered. Three new sites (Isosuo, Tremanskarr and Kantosuo) were investigated in detail by means of stratigraphic, biostratigraphic and morphometric analyses; other material was collected from existing written sources. The first peats began accumulating in the region about 10 700 cal. BP. Two distinct phases of more intensive peat initiation, followed by subsequent spread, were recognized: c. 8000-7300 cal. BP and from c. 4300 cal. BP onwards (mainly 4300-3000 cal. BP). This pattern may well reflect the increased humidity at those points in time, and show a striking similarity to the pattern of change in lake levels in southern Sweden. In all cases the peat initiation was evidently governed not only by climate but by a wealth of internal and external factors, complicating the evaluation of past influences of climate. However, results demonstrate the potential of basal peats as a source of proxy climatic data.