A qualitative study of wood charcoal that is dated to the time of the Toba volcano super-eruption from Sibudu and Border Caves, South Africa

Zwane, Bongekile
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The Toba volcano super-eruption, dated to 74 000 years old (74 ka), is often credited for limiting the contribution of some non- Homo sapiens hominins to the contemporary human gene pool. This follows the hypothesis that hominin populations who lived outside Africa perished due to the global ‘volcanic winter’ that resulted from this event, while Homo sapiens populations in Africa decreased drastically. The debate about the impact of the Toba super-eruption on global climate was revived recently following the discovery of its volcanic ash on the south Coast of South Africa. I, therefore, investigated if devastating ‘volcanic winter’ conditions that are associated with the Toba super-eruption were present in south-east Africa between 74 and 72 ka. The aim was to test if such conditions affected the growth of woody vegetation, as well as the people who depended on it, using wood charcoal that is preserved at Sibudu and Border Caves, KwaZulu Natal Province. I applied standard archaeobotanical and anthracological procedures while analysing and interpreting charcoal data. I identified two different types of forested landscapes around the caves, which are located 300 km apart. At Sibudu Cave, there was, predominantly, Afromontane and Scarp Forests with Savanna vegetation, while the Border Cave’s landscape had much Savanna, Montane Forest and Grassland woody species. There were warm and humid conditions at Sibudu, which persisted between 73 and 72 ka, based on a range of active fungi in the wood. At Border Cave, there was seasonal fluctuation of unknown environmental conditions, but also warm temperatures that promoted partial silicification of some wood specimens ~ 74 ka. These results, along with other environmental data, suggest no substantial evidence for extended ‘volcanic winter’ conditions in KwaZulu Natal. However, more work is needed in other parts of southern Africa because it is suspected that people’s movements at this time may be related to unfavourable conditions elsewhere in the subcontinent. The absence of environmental stress in KwaZulu Natal may be due to a stronger influence of local climate drivers which prevented the full impact of the Toba super eruption from overwhelming southern Africa, such that people had resources on which they could depend.
A thesis submitted in fulfilment of the academic requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Geosciences, University of the Witwatersrand, Johannesburg, 2022