For about the last 30 years it has been recognized that the high frequency component of the tree rings
14C/
12C record is dominated by the modulation of the cosmic ray flux by the solar wind. In particular, it has been demonstrated that the three most recent periods of low sunspot occurrence were characterized by high values of atmospheric
14C/
12C. During the last millennium other periods of high
14C/
12C values were observed but their solar origin is still debatable. In the present work we compare these fluctuations with an independent record of cosmogenic
10Be measured in ice from the South Pole to check the solar origin of the observed
14C/
12C variations. In order to compare quantitatively the results obtained on
10Be and
14C, it is necessary to take into account the different behaviour of these two cosmogenic isotopes, and especially the damping effect of the carbon cycle in the case of
14C. As an input to a 12-box numerical model we used the relative fluctuations of the
10Be concentrations record measured in South Pole ice and converted it into a synthetic
14C record. We took into account the fact that
10Be modulation is enhanced in polar regions due to the orientation of the geomagnetic field. As expected, the fluctuations of the modelled
14C record are much smaller (a factor of 20) than those observed for the raw
10Be record. In addition, the variations are smoother and shifted in time by a few decades. The
10Be-based
14C variations closely resemble the
14C measurements obtained on tree rings (R = 0.81). In particular, it is easy to identify periods of maximal
14C/
12C which correspond to solar activity minima centred at about 1060, 1320 (Wolf), 1500 (Spörer), 1690 (Maunder) and 1820 (Dalton) yr A.D. Cross-correlation calculations suggest that there is no significant lag between the
10Be-based
14C and the tree-ring
14C records. Our study strongly suggests the dominance of the solar modulation on the cosmonuclide production variations during the last millennium.
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