The aridification of Eastern Africa

Published: 5 November 2021

Where else to look for changes in the earth’s climate than the ocean? The seabed contains much information on how the world’s climate has changed over the millennia. It recently revealed how the climate of Eastern African changed from wetter conditions to the arid conditions we know today. An article in Nature entitled ‘Indo-Pacific Walker circulation drove Pleistocene African aridification’, co-written by Deltares’ Björn Backeberg, explains how the authors looked to the seabed to discover that a shift in air circulation about two million years ago is likely to have brought about this change.

Eastern Africa’s current arid climate is caused by the Indo-Pacific Walker air circulation which transports warm moist air across the Indian Ocean from east to west. During the journey, much of the moisture is lost and by the time it reaches the Eastern African coast – on the western reaches of the Indian Ocean – it is dry. This is the climatic situation today and over the last few hundreds of thousands of years.

Finding clues in fluctuations of ocean water flow

We know that the climate in Eastern Africa used to be much wetter and Backeberg and his co-authors were intrigued to find out how and when the change came about. So they drilled a marine core from the seabed of the Mozambique Channel between Madagascar and Mozambique and closely examined its sediments, looking for fluctuations in the speed of ocean water flow which would give a clue to changes in the circulation pattern. They looked back an incredible seven million years. For much of that time the Mozambique Channel Throughflow revealed a weak steady flow. Then, a little over two million years ago, the Indo-Pacific Walker air circulation started to intensify during glacial periods. At the same time the Mozambique Channel Throughflow started to increase and the air became drier. The authors hypothesise in their study that the two phenomenon are connected. They also suggest that the change in climate may have influenced human evolution in East Africa and even allowed humans to expand their territory around the world.

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Full article in Nature “Indo-Pacific Walker circulation drove Pleistocene African aridification
Authors: H. J. L. van der Lubbe, I. R. Hall, S. Barker, S. R. Hemming, T. F. Baars, A. Starr,
J. Just, B. C. Backeberg & J. C. A. Joordens