CONTROL OF SOLAR RADIATION OVER CLIMATE VARIABILITY IN SOUTHERN AFRICA: ISOTOPIC AND PETROGRAPHIC EVIDENCE FROM NAMIBIA AND BOTSWANA STALAGMITES

Paleoclimate proxies from speleothems reveal a strong relationship between the variation in solar radiation and the climate response in Southern Africa. Climate in southern Africa is characterized by a high degree of spatial and temporal variability. El-Nino Southern Oscillations (ENSO), changes in monsoon strength, and the migration of the Inter-Tropical convergence Zone (ITCZ) are the well-known climatic factors controlling these variations. Other significant climatic factors, causing significant climatic change, known in the northern Hemisphere were also interpreted to contribute to abrupt climatic change in Africa, but thus far little is known about the relationship between the change in solar radiation, which is known to play an important role in controlling the strength of the Indian Monsoon and the climatic response in Southern Africa. Here we investigate two stalagmites from Namibia and Botswana at very high resolution to better understand this relationship for the last 1400 yr AD (500 yr. BP). We collected isotopic data along with radiometric ages to understand the pattern of paleoclimate variability in these two locations, and examination of layer-bounding surfaces (Railsback et al., 2013) shows that Type E surfaces indicative of wetter conditions coincide with minima in d¹⁸O, and Type L surfaces indicative of drier conditions coincide with maxima in d¹⁸O. The results primarily suggest that climate in Southern Africa was wetter during sunspot minimums (Maunder and Spörer) and drier during periods between sunspot minima. Reduced solar insolation is known to reduce the strength of the Indian Monsoon, and it has been reported that western India was dry during these minima. The dry vs. wet climatic response in India and Southern Africa specifically satisfies the general circulation pattern (wind and sea surface temperature) and land response to climate change observed within the northern part of the warm Indian Ocean pool. This means that during sunspot minima, the Indian Monsoon is weaker and climate in the Indian landmasses is drier, while that of Southern Africa becomes wetter. And the opposite is true between these sunspot minima. We therefore conclude that solar insolation is one factor controlling the climate variability in southern Africa by controlling the strength of the Indian Monsoon.