Africa is home to varied climate systems, with the wettest part of the continent being where trade winds meet, at a tropical rain belt near the equator called ‘Inter-tropical Convergence Zone’ (ITCZ).
In southwest Africa, climate of northeastern Namibia is sensitive to changes associated with the ITCZ. It is prone to desertification in dry years. Looking at past climatic histories through the geological record (paleoclimate), we can predict how this area may be affected in the future by climate change. A more accurate prediction consists of filling gaps in Namibia’s paleoclimate records. Dr Ny Riavo Voarintsoa and her colleagues have helped to do so through careful paleoclimatic analysis of a stalagmite from Dante Cave, to find out about patterns of past dry and wet periods in the region.
Little Ice Age and modern climate warming
One of these periods was the Little Ice Age (LIA), marked by exceptionally low temperatures and possibly low solar activity in the Northern Hemisphere (NH) during the 16th-mid 19th century. It brought about humidity in the Southern Hemisphere since the ITCZ migrated southwards in response to the cooling of the NH. Thenceforth, it moved relatively northward, leaving the region with warmer and drier climate.
Stalagmites may tell us about past environmental histories through their stable isotopes, petrography, and mineralogy, as Voarintsoa commented: “Stalagmites can be dated with precision and accuracy”, and our team members, including Hai Cheng and Lawrence Edwards, are leading experts on it. Voarintsoa’s team analysed the uppermost part of a stalagmite from Dante Cave, focusing on a small time-frame, to see how cooling impacted northeastern Namibia between AD 1400 and 1950. The team confirmed the stalagmite age using the uranium-thorium pair method while comparing stable isotopes, petrographic, and mineralogical results with established temperature and solar activity data.
What the researchers uncovered
The team successfully married a link from changing climate and rainfall patterns in northeastern Namibia, with solar activity and global temperature change. They showed that during low levels of solar activity and global cooling, like during the LIA, there were wetter periods in northeastern Namibia, due to a movement of the ITCZ to the southwest. After 1715, warming coincided with the northeasterly movement of the ITCZ, causing reduced rainfall of the summer rainfall zone of southern Africa in more recent years.
Implications for the future
Voarintsoa noted a finding of “an increasing oxygen isotopic trend starting from 1750 to 1950 that is coeval with the global increase in temperature”. This warmer climate in the NH may have induced warmer, drier conditions in northeast Namibia, as the ITCZ shifted northwards. This implies that with further warming trends in the high latitude regions of the Northern Hemisphere, northeast Namibia may become even warmer and drier in the future.
- Voarintsoa, N. R. G., Brook, G. A., Liang, F., Marais, E., Hardt, B., Cheng, H., Edwards, R. L., and Railsback, L. B. (2017). ‘Stalagmite multi-proxy evidence of wet and dry intervals in northeastern Namibia: Linkage to latitudinal shifts of the Inter-Tropical Convergence Zone and changing solar activity from AD 1400 to 1950’. The Holocene, v. 27, no. 3, p.384-396. doi:10.1177/0959683616660170
Dr Ny Riavo Voarintsoa and her colleagues are looking at past climatic histories in northeast Namibia through the geological record (paleoclimate) in order to try to predict how this area may be affected in the future by climate change.
- Schlumberger Foundation Faculty for the Future to Ny Riavo G. Voarintsoa
- NSF 0002193 to George A. Brook
- Natural Science Foundation of China Grant NSFC 41230524 and NSFC 41731174 to Hai Cheng.
- George A. Brook
- L. Bruce Railsback
- Fuyuan Liang
- Eugene Marais
- Benjamin Hardt
- Hai Cheng
- R. Lawrence Edwards
Ny Riavo Voarintsoa (aka. Voary) obtained her PhD degree in Geology from the University of Georgia in 2017. Her study focused on reconstructing environmental and climate changes throughout history in Southern Africa and Madagascar using stalagmites. Currently, she is a post-doctoral fellow at the Hebrew University of Jerusalem and has recently been awarded a Marie Curie Fellowship to undertake research in her home country, Madagascar.
Dr Ny Riavo Voarintsoa
The Fredy & Nadine Herrmann
Institute of Earth Sciences
The Hebrew University of Jerusalem
Edmond J. Safra Campus
Jerusalem, Israel. 91904
T: +972 5867 68916