A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab (Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.
iThemba LABS, Private Bag 11, Wits 2050, South Africa;Mammal Research Institute, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa;Mammal Research Institute, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa;Department of Geography, Swansea University, Swansea SA2 8PP, United Kingdom;Faculty of Chemistry, Babes-Bolyai University, Arany Janos 11, 400028 Cluj-Napoca, Romania;Nansen-Tutu Center for Marine Environment, University of Cape Town, Cape Town, South Africa;Dept of Oceanography, Mare Institute, University of Cape Town, Cape Town, South Africa;Department of Geography, Swansea University, Swansea SA2 8PP, United Kingdom;SANParks Scientific Services, Pvt Bag X402, Skukuza, 1350, South Africa
Recommended Citation:
Stephan Woodborne,Grant Hall,Iain Robertson,et al. A 1000-Year Carbon Isotope Rainfall Proxy Record from South African Baobab Trees (Adansonia digitata L.)[J]. PLOS ONE,2015-01-01,10(5)