RADIOCARBON VARIATIONS IN ANNUAL TREE RINGS WITH 11-YEAR SOLAR CYCLES DURING 1800–1950

ABSTRACT The results of radiocarbon variation studies observed in annual tree rings from the NW Pacific (USA Northwest) (Stuiver and Braziunas 1993) and Europe (England, Brehm et al. 2021; Slovakia, Povinec 1977, 1987) are reviewed with the aim of better understanding the 11-year radiocarbon cycle and possible impacts of solar proton events on 14 C levels in the atmosphere and biosphere. The average Δ 14 C amplitude in tree rings for the period of 1798–1944 was 1.3 ± 0.3‰, the average periodicity was 11 ± 1 years, and the average time shift between the sunspot numbers and Δ 14 C records was 3 ± 1 years. A new solar activity minimum (Gleissberg minimum, 1878–1933) has been identified in the Δ 14 C data sets from the NW Pacific and England, showing Δ 14 C excess of 7‰, comparable to the Dalton minimum (1797–1823). No significant changes in Δ 14 C levels were identified that could be associated with solar proton events during 1800–1950.