Δ¹⁴C and δ¹³C in Annual Tree-Ring Samples from Sequoiadendron Giganteum, AD 998-1510: Solar Cycles and Climate

Time series of annual Δ¹⁴C and δ¹³C in tree rings of Sequoiadendron giganteum, AD 998-1510, are similar in form. The Δ¹⁴C series completes, with data of Stuiver and Braziunas (1993), a 957-yr time-series. Discrete Fourier transformation of detrended Δ¹⁴C reveals periods of 126, 91, 56, 17.6, 13.6, 10.4, and 7.1 yr. Non-random differences exist between decadal averages of the Sequoiadendron Δ¹⁴C data and data of Stuiver and Becker (1993). Periods of 7-17 yr may correspond to Schwabe or related climatic cycles; these have 10-17-yr periods and amplitudes < 6‰ (AD 1100-1250), and periods near 7 yr with amplitudes up to 10‰ (AD 1380-1420). Abrupt increases in Δ¹⁴C are mainly less than 5‰, and do not constitute convincing evidence of increased ¹⁴C production from supernovae or solar proton events. The δ¹³C time-series is likely to reflect climate change, and for centennial periodicity lags behind Δ¹⁴C by 20-40 yr (centennial time-scale) and 25-50 yr (millennial). Phase-shifts between solar luminosity and surface Δ¹⁴C are 125-175 yr and 20 yr for millennial and centennial cycles, respectively. The study suggests that strongest climate effects may therefore follow peak luminosity by 125-175 yr for millennial cycles and 20-40 yr for centennial cycles.