400 YEAR RECORD OF DELTA-C-14 IN TREE-RINGS - THE SOLAR-ACTIVITY CYCLE BEFORE, DURING AND AFTER MAUNDER MINIMUM AND THE LONGER CYCLES

The analysis of Delta(14)C in dated tree ring series from 1600 to 1940 AD is presented. The data series is divided into two parts, namely be fore and after 1780 AD to better study the characteristic of its cycli cities before, during and after the Maunder Minimum period. The data a fter 1780 AD show the presence of significant cyclical variations in t he 10-12 year range, similar to the ones observed in other solar-activ ity index series. On longer time scales, only the <<Gleissberg>> cycle , which appears to modulate the 11 y cycle, seems to be significant. T he origin of this last fluctuation in radiocarbon production is influe nced by cosmic-ray intensity variations connected to long-term solar-w ind flux variations. The analysis of Delta(14)C in two independent ser ies of dated tree rings during 1564-1780 AD shows that there is an enh ancement in radiocarbon level during the Maunder Minimum. Our data sho w that there are time variations of C-14 production rate even during t he Maunder Minimum, as cosmic rays were modulated by the Sun in spite of the very low solar activity.