Ancient rivers show several greens in the Sahara desert

Ancient rivers show several greens in the Sahara desert

A giraffe painting from an era of the Green Sahara. Credit: Mike Hettwer (http://hettwer.com)

Large parts of the Sahara desert were green thousands of years ago, evident from prehistoric engravings in giraffes, crocodiles and a stone age cave painting of people swimming. Recently, more detailed insights have been gained from a combination of sediment cores extracted from the Mediterranean and the results of climate computer modeling, led by an international research team, including the University of Hawaii in Manao oceanography researcher Tobias Friedrich, for the first time. investigated.

The layers of the seabed tell the story of major changes in the environment in North Africa over the past 160,000 years. The study, co-authored by Friedrich and led by Cécile Blanchet of the German Geosciences Research Center GFZ, was published in Natural Sciences.

Climate context for previous populations

Together with the GEOMAR Helmholtz Center for Ocean Research Kiel, a team of scientists organized a research voyage to the Libyan Gulf of Sirte.

“We suspected that when the Sahara Desert was green, the rivers that are currently dry would have been active and brought particles into the Gulf of Sirte,” Blanchet said.

The analysis of such sediments will help to better understand the timing and conditions for the reactivation of these rivers and provide a climate context for the development of populations in the past.

Using a method called suction barrier, the scientists pushed giant cylinders into the seabed and were able to recycle nearly 30-foot-long columns of marine mud.

The mud layers contain sediment particles and plant debris transported from the nearby African continent, as well as shells of microorganisms that have grown in seawater, and tell the story of climate change in the past.

“By combining the sediment analyzes with the results of our computer simulation, we can now understand the climatic processes at work to explain the drastic changes in North African environments over the past 160,000 years,” Friedrich said.

Ancient rivers show several greens in the Sahara desert

Piston core, wrapped in yellow, awaits analysis. In the background: lead author Cécile Blanchet. Credit: University of Hawaii at Manoa

Climate change could cause migrations

From previous work, it was already known that several rivers flowed episodically across the region, which today is one of the driest areas on earth. The team’s unprecedented reconstruction covers the past 160,000 years. It provides a comprehensive picture of when and why there was sufficient rainfall in Central Sahara to reactivate these rivers.

“We have found that it is the slight changes in the orbit of the earth and the shrinking and wilting of polar ice sheets that have led to the alternation of moist phases with high precipitation and long periods of near complete drought,” Blanchet explained.

The fertile periods generally lasted five thousand years and the humidity spread over North Africa to the Mediterranean coast. For the people of that time, it resulted in drastic changes in living conditions, which probably led to major migration movements in North Africa.

“With our work, we have added some essential puzzle pieces to the picture of past Saharan landscape changes that help to better understand human evolution and migration history,” Blanchet said. “The combination of sediment data with computer simulation results has been crucial to understand what has controlled the succession of moist and dry phases in North Africa during the past. This is especially important as this region is expected to experience intense droughts. experienced as a result of human climate change. ”


Study shows that the Sahara swung between lush and desert conditions every 20,000 years, in line with monsoon activity


More information:
Cécile L. Blanchet et al. Managers of river reactivation in North Africa during the last glacier cycle, Natural Sciences (2021). DOI: 10.1038 / s41561-020-00671-3

Provided by the University of Hawaii at Manoa

Quotation: Old Rivers Reveal Multiple Greens of the Sahara Desert (2021, January 29) Retrieved January 29, 2021 from https://phys.org/news/2021-01-ancient-rivers-reveal-multiple-sahara.html

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