Identification of solar periodicities in southern African baobab δ13C record

Pieter B Kotzé

doi:10.17159/sajs.2020/6813

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.

Highlights

Carbon isotope ratios have been used in the literature[1] by several palaeoclimate researchers as a proxy for rainfall in a specific region where data were made available by tree ring investigations
The ~18-year period which is characteristic of southern African rainfall could be verified
The ~18-year period which is characteristic of southern African rainfall, could be identified in our spectral analysis, confirming previous investigations of the rainfall pattern across this region

Summary

Introduction

Carbon isotope ratios have been used in the literature[1] by several palaeoclimate researchers as a proxy for rainfall in a specific region where data were made available by tree ring investigations. Spectral analysis methods such as wavelets[18], Lomb–Scargle[19,20] and maximum entropy[21] were used to obtain statistically significant results above the 95% confidence level. This particular interval coincides with the sunspot Maunder Minimum (1645–1715 AD) when no sunspots could be observed on the surface of the sun and was known as the Little Ice Age. In the northern hemisphere, extreme cold spells were experienced during the Little Ice Age. It is quite extraordinary that a disappearance of the 11-year Schwabe cycle on the sun did coincide with a similar pattern in the δ13C data obtained from the summer rainfall region of southern Africa.

Results

Conclusion