Cyclicity of Solar Activity During the Maunder Minimum Deduced from Radiocarbon Content

This paper presents the features of the “eleven-year” cycle of radiocarbon content during the period of prolonged sunspot minimum called the Maunder Minimum (1645–1715 AD). Whether or not the Sun had maintained the cyclic polarity reversal even during the Maunder Minimum has been a controversial topic for a long time. Although persistency of the cyclicity has been investigated by using cosmogenic isotopes or by calculations, a consistent description has not been obtained so far. Hence, we have obtained a new record of carbon-14 content in tree rings from 1631–1739 AD, and made a comparison with the record previously obtained. Periods of 13–15 and 24–29 years detected in the variation of carbon-14 content seem to be suggesting that the Sun had retained periodic polarity reversal during this prolonged minimum with slightly longer periodicity than that of recent intense solar activity. Our results seem to support the inverse correlation between the intensity and the cycle length of solar activity.