Variations in Solar Activity Across the Spörer Minimum Based on Radiocarbon in Danish Oak

Several aspects concerning the origin and nature of grand solar minima remain unclear, andmore high-resolution10Be and14C records are needed to improve our understanding of these phenomena.Here, we report 137 new high-precision, annually resolved radiocarbon concentrations based on oak fromthe Danish dendrochronology. The new record covers a period (CE 1432–1578) that encompasses most ofthe penultimate grand solar minima known as the Spörer Minimum. A detailed comparison between theSpörer and Maunder (CE 1640–1720) minima shows that the Spörer Minimum is associated withenhancedΔ14C variability in a band centered around the 11-year Schwabe cycle from CE 1450 to 1479 andbetween CE 1545 and 1578, whereas little 11-year variability is observed from CE 1479 to 1539. In contrast,we only observe enhanced 11-year variability after the end of the Maunder Minimum at CE 1722–1744,which could indicate that the nature and origin of the two minima were different.