Clocking speed of ocean circulation holds key to past African climates

Cardiff University

Scientists have identified a new mechanism to account for the drastic aridification in eastern Africa over the past two million years, with likely implications for understanding the evolution and dispersal of our early human ancestors.

In a study published today in Nature, a team led by scientists at Cardiff University propose that roughly 2.1 million years ago, changes in the speed of Indian Ocean waters through the Mozambique Channel were synchronized with the onset of the east-to-west atmospheric circulation pattern along the Pacific Ocean.

This so-called Walker circulation resulted in subsequent changes in the Indian Ocean region causing dry spells in eastern Africa during glacial periods.

The study also found that the increasingly dry and cold spells were punctuated by wetter and warmer periods. The team say that ultimately, their results could contribute to understanding and explaining why humans first dispersed beyond Africa around this time.

As part of the study, a sediment core was taken from the Mozambique Channel – a 1,600 km-long arm of the western Indian Ocean located between Madagascar and Mozambique. Using tiny fossils of single-celled organisms known as foraminifera, as well sediments taken from the core, the team reconstructed the flow speed of the ocean’s circulation extending 7 million years into the past.

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