SECULAR AND LARGE-SCALE CHANGES IN SOLAR ACTIVITY, COSMOGENIC ISOTOPES AND CLIMATE CHANGES V.A.Dergachev

Abstract. There is a grows body of evidence from a multi-proxy palaeoclimate records that hundred years and millennial years periodic climatic events have persisted during the last 10000 years, as for instance the well-known “Little Ice Age ” and cold episode about 2800 cal yr BP separated by about 2400-year time interval. Ice rafted debris in marine cores of the north Atlantic, which are attributed to changes in the north Atlantic deep water formation and probably forced by changes in solar activity, demonstrated about 1500-year cycles, which rather appear to reflect atmospheric circulation variations, ice sheet fluctuations and oceanographic changes. It is well established that the production of cosmogenic isotopes, such as 14C and 10Be, is modulated by solar activity and may thus serve as a proxy for solar activity changes. The 14C and 10Be signals from well-dated samples show similar trends during the last 10000 years. Removing the effects of the Earth’s magnetic field from the measured 14C concentration in tree-ring yields the residual radiocarbon signal, which potentially reflects changes in solar activity. As demonstrated by spectral analysis of sunspot numbers and reflected in the 14C proxies, solar activity displays a cyclic behavior with short-time, secular and large-scale periodicities. Hence, if solar activity is the driving force behind climate changes, these cyclicities should be observable in climate records. Evidence of warm and cold periods and of cyclic climate variability connected with secular and large-scale changes in solar activity are demonstrated by this work. Large-scale climate changes recognized as global events suggest periodicities of about 2400 years. The observed 210-year climate periodicity corresponds to secular changes in solar activity, such as the Maunder or Spoerer minimum. Direct solar forcing may account for a significant amount of the climate variations observed during the Holocene