Past river activity in northern Africa features a number of Saharan greens

Large parts of the Sahara desert today were green thousands of years ago. Prehistoric carvings of giraffes and crocodiles confirm this, as does a stone-age cave painting in the desert that even shows people swimming. However, these images only give a rough picture of the living conditions. More recently, more detailed views have been obtained from sedimentary rocks extracted from the Mediterranean Sea off the coast of Libya. An international research team studied these rights and found that the layers of the seabed tell a story of major environmental changes in North Africa over the past 160,000 years. Cécile Blanchet from the German Research Center for GFZ Geology and her colleagues from Germany, South Korea, the Netherlands and the USA report on this in the journal Geology of nature.

Together with the GEOMAR Helmholtz Center for Kiel Ocean Exploration, a team of scientists organized a research cruise on the Dutch ship Pelagia to the Gulf of Sirte in December 2011. “We had a suspicion when the Sahara Desert was green, the rivers that are currently dry it would have been active and would have introduced grains into the Gulf of Sirte, ”says lead author Cécile Blanchet. Such sediments would help to better understand the timing and location for the reactivation of these rivers.

Using a method known as “piston coring”, scientists were able to retrieve 10-meter-long columns of sea length. “A large empty cylinder can be thought of as being pushed into the seabed,” said co-author Anne Osborne of GEOMAR, who was on board the research vessel. “The seabed layers contain rock fragments. and plant remains transported from a nearby African continent. They are also full of shells of microorganisms grown in seawater. Together, these sediment particles can tell us the story of climate change, “Blanchet explained.

“By combining the sediment analyzes with results from our computer simulation, we can now understand the climate processes at work to bring about the dramatic changes in North African environments across explain the past 160,000 years “, adds co – author Tobias Friedrich of the University of Hawaii. ‘i.

From previous work, it was already known that several rivers flowed throughout the area, which is today one of the driest areas on Earth. The team’s unique reconstruction covers the past 160,000 years. It provides an overview of when and why there was enough water in Central Sahara to reactivate these rivers. “We found that the small changes in the Earth’s orbit and the erosion and erosion of polar ice sheets reduced moisture levels with high precipitation and prolonged periods of unsightly beauty. very complete ”, explained Blanchet.

Fertility periods typically lasted five thousand years and moisture spread over North Africa up to the Mediterranean coast. For the people of that period, this caused major changes in living conditions, which could lead to major migration movements in North Africa. “Through our work we have added some essential jigsaw puzzles to the picture of past Saharan landscape changes that will help to understand human evolution and the history of migration,” Blanchet said. The combination of sediment data with computer simulation results was crucial to understanding what controlled the continuity of damp and arched levels in North Africa. This is particularly important as this area is expected to experience severe drought as a result of human-induced climate change. ”

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