Radiocarbon variations with the 11-year solar cycle during the last century

Abstract

As ¹⁴C is produced in the atmosphere by interactions between neutrons and nitrogen atoms, changes in the cosmic ray flux associated with the 11-yr solar cycle will produce variations in ¹⁴C production with the same period¹. These variations are difficult to observe because the atmosphere acts as a low-pass filter, greatly attenuating their amplitude². Previous investigations on short-term ¹⁴C variations in tree rings either reported no correlation with the 11-yr solar cycle^3–5 or found a correlation with an average amplitude of 1.5 to 3‰ (refs 6–10). However, Baxter et al. reported an average amplitude of about 10‰ in tree rings^11,12 and in samples of whiskies, wines and plant seeds¹³, and Lavrukhina et al.¹⁴ found a 10‰ correlation amplitude in wood samples. However, very precise ¹⁴C tree-ring measurements reported more recently^15–17 show only minor short-term ¹⁴C variations. A comparison of resultsobtained by Stuiver¹⁵ and Baxter et al.¹¹ suggests that the larger ¹⁴C fluctuations found by the latter group may be due to a lower precision of their ¹⁴C measurements. Here we have dated wines from the period 1909–52 and our results show ¹⁴C variations with an average amplitude of 4.3±1.1‰ during the 11-yr solar cycle.