Recurring variations of probable solar origin in the atmospheric Δ¹⁴C time record

After removal of the ∼ 11,000‐year geomagnetic contribution to a relatively high‐precision atmospheric Δ¹⁴C record covering the past 7200 years, residual variations exhibit a 2200–2600 year quasi‐periodicity that has been recognized in earlier studies. We find here that century‐scale variations in the most recent ‘cycle’ are positively correlated with similar short‐term variations in each of the two previous cycles. Thus the quasi‐periodicity consists of both a long‐term variation of the mean and a superposed, approximately recurring pattern of century‐scale variations. The strongest of these latter variations occur near successive maxima of the ∼ 2400 year cycles. During the last millennium, the largest century‐scale variations (occurring near the most recent 2400 year maximum) are known to be mainly a consequence of the pronounced Maunder, Spörer, and Wolf solar activity minima. Therefore, the recurrence of large amplitude Δ¹⁴C variations at 2400 year intervals is most directly explained as due to solar forcing at both the ∼ 2400 year and century‐scale periods. A fully terrestrial 2400 year modulation of an independent century‐scale solar forcing function is disfavored by the joint occurrence of relatively strong Δ¹⁴C maxima and solar activity minima during the current millennium, according to independent proxy records. The probable existence of a ∼2400 year solar quasi‐cycle has implications for the predictability of future pronounced solar activity minima and for the interpretation of certain minor Holocene climatic variations.