Rainfall control of the δ13C ratios of Mimusops caffra from KwaZulu-Natal, South Africa

Abstract

High-precision radiocarbon dating of individual growth rings demonstrates that Mimusops caffra produces annual growth rings. Direct comparison of the carbon isotope composition of the annual rings from two specimens from the northern coast of KwaZulu-Natal, South Africa, with the historic climatic record that exists from AD 1927, shows a response to the amount of rainfall recorded for each year. The δ13C response is particularly sensitive to extreme events such as tropical cyclones and droughts. It is demonstrated that whole wood samples provide an accurate record of climatic conditions. Although the result allows long-term periodicity in rainfall to be determined over the 134 years during which the oldest tree grew, the last 20 years is overprinted with a δ13C shift of anthropogenic origin. Signal processing approaches allow the interannual rainfall response to be separated from the long-term anthropogenic influences.