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Description
Cosmogenic isotopes provide the only quantitative proxy to analyze the long-term solar variability over the centennial time scale. While an essential progress has been achieved in both measurements and modelling of the cosmogenic proxy, uncertainties still remain in the determination of the geomagnetic dipole moment evolution. Here we aim at improving the reconstruction of solar activity over the past nine millennia using a multi-proxy approach. We use records of the ^14^C and ^10^Be cosmogenic isotopes, up-to-date numerical models of the isotope production and transport in the Earth's atmosphere, and available geomagnetic field reconstructions, including a new reconstruction relying on an updated archeo/paleointensity database. The obtained series were analyzed using the SSA (Singular Spectrum Analysis) method to study the millennial-scale trends. A new reconstruction of the geomagnetic dipole field moment, referred to as GMAG.9k, is built for the last nine millennia. New reconstructions of solar activity covering the last nine millennia, quantified in terms of sunspot numbers, are presented and analyzed. A conservative list of Grand minima and maxima is also provided. The primary components of the reconstructed solar activity, as determined using the SSA method, are different for the ^14^C and ^10^Be based series. This shows that these primary components can only be ascribed to long-term changes in the terrestrial system, and not to the Sun. These components have therefore been removed from the reconstructed series. In contrast, the secondary SSA components of the reconstructed solar activity are found to be dominated by a common ~2400-year quasi-periodicity, the so-called Hallstatt cycle, in both the ^14^C and ^10^Be based series. This Hallstatt cycle thus appears to be related to solar activity. Finally, it is shown that the Grand minima and Grand maxima occurred intermittently over the studied period, with clustering near highs and lows of the Hallstatt cycle, respectively.
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