Identification of solar periodicities in southern African baobab δ13C record

Abstract

Spectral analysis using wavelet, Lomb–Scargle and maximum entropy techniques of the proxy rainfall record of northeastern South Africa based on annual carbon isotope (δ¹³C) data obtained from baobab trees for the period 1600 AD – 2000 AD show clear evidence of the presence of characteristic solar periodicities. Solar periodicities that were identified above the 95% confidence level include the ~11-year Schwabe cycle, the ~22-year Hale cycle as well as the 80–110-year Gleissberg cycle. A Morlet wavelet analysis of the δ¹³C data between 1600 AD and 1700 AD shows the effect of the Maunder sunspot minimum on both the Schwabe and Hale cycles during this time.

Significance:

• A spectral analysis of δ¹³C baobab tree ring data for southern Africa between 1600 AD and 2000 AD is presented. The results show – for the first time – that the δ¹³C time series contains the 11-year Schwabe, 22-year Hale as well as the 80–110-year Gleissberg solar periodicities. In addition, the influence of the Maunder sunspot minimum between ~1650 AD and 1715 AD could also be clearly identified in the δ¹³C data for the first time. These findings are of significant importance to investigations of solar influences on climate variability.