Climatic Changes in Northern Europe Since Late Glacial Times, with special reference to dendroclimatological studies in northern Finnish Lapland

摘要

The oxygen isotope variations in deep Greenland ice cores indicate large and extremely rapid temperature oscillations during the last ice age. Strongly fluctuating climatic conditions also characterized the final few thousand years of the Weichselian glaciation. Temperatures rose to levels near their present values during the Boelling-Alleroed interstadial, but during the Younger Dryas episode (12,700 -11,500 years ago) the cold ice age conditions came back. The cold spell ended with an abrupt warming about 11,500 years ago and it marked the beginning of the present warm interglacial, the Holocene. The Holocene climate has also varied, but all oscillations in temperatures have been an order of magnitude smaller than those common in the North Atlantic region during the last ice age. Temperatures rose to about present-day values in early Holocene time and generally continued to rise slowly until 6000 - 5000 BP. During the last 5000 years climatic conditions have gradually become cooler and obviously somewhat more unstable. The variations in humidity show some differences in various regions of Fennoscandia, but since 2500 BP, wetness has generally increased. There are different climatic proxy data which can be used for Holocene studies, but the extraction and interpretation of signals of small short-term changes is often difficult because of unavoidable inaccuracies in data and dating. The main trends of Holocene climatic development are relatively well known over northern Europe, but the short-term variations are not known in detail. Tree rings provide a possibility to study high-frequency climatic variability, since annual and even seasonal resolution in dating can be achieved using dendrochronology. The pine tree-ring data collected from the tree-line area of northern Fennoscandia indicate changes in past summer temperatures. The absolute tree-ring curve constructed from subfossil pines fPinus sylvestris, L.) of Finnish Lapland indicates a duration of over 2000 years, extending to 165 B.C. and, after a ca. 200-year gap, the older unbroken part of the chronology extends until about 7500 calendar years before present. Preliminary interpretations of the data suggest that the climatic variability in the study area increased around 5000 BP with a subsequent trend towards cooler and wetter climatic conditions.