On solar forcing of Holocene climate: evidence from Scandinavia

Abstract

The focus of this study is the possible correlation between changes in the climate of Scandinavian and changes in solar irradiation. Reliable information about Holocene climatic change in Sweden and Norway is currently available from two main sources: the 14 C dating of pine wood retrieved from above the present pine-tree limit and studies of glacier variations based on proglacial lacustrine sediments and on moraines. The reconstructed alpine tree-limit reveals that summer temperature in general was warmer during the early Holo cene than it was during the late Holocene. Superimposed on this general trend are several fluctuations of a few hundred years' duration. Relatively cold periods with a duration of the order of 300-600 years occurred frequently during the Holocene. In this paper, dates of the major climatic events are compared with an index of solar activity, the so-called δ 14 C anomalies. For most of the last 9000 years a good correspondence is demonstrated between the timing of cold events in Scandinavia and the timing of major δ 14 C anomalies (low solar irradiation). The general Holocene cooling trend is believed to be partly a result of land uplift following deglaciation and partly a result of orbitally forced changes in irradiation. Large fluctuations in Scandinavian summer temperature can be reconciled with the pattern of climatic change presented in several recent studies in the North Atlantic region. A link between these areas could be provided by changes in the production of North Atlantic Deep Water.