© Peter deMenocal
The multicorer device being lowered into the ocean takes eight one-foot cores from the seafloor. Scientists analyze such cores for clues to the climate of the past several thousand years.
Rainfall patterns in the Sahara during the 6,000-year "Green Sahara" period have been pinpointed by analyzing marine sediments, according to new research.
What is now the Sahara Desert was the home to hunter-gatherers who made their living off the animals and plants that lived in the region's savannahs and wooded grasslands 5,000 to 11,000 years ago.
"It was 10 times as wet as today," said lead author Jessica Tierney of the University of Arizona. Annual rainfall in the Sahara now ranges from about 4 inches to less than 1 inch (100 to 35 mm).
Although other research had already identified the existence of the Green Sahara period, Tierney and her colleagues are the first to compile a continuous record of the region's rainfall going 25,000 years into the past.
The team's paper "Rainfall regimes of the Green Sahara," is scheduled for publication in the journal
Science Advances on Jan. 18.
Archaeological evidence shows humans occupied much of the Sahara during the wet period, but left for about a thousand years around 8,000 years ago—the middle of the Green Sahara period.
Other investigators have suggested the Sahara became drier at the time people left, but the evidence was not conclusive, said Tierney, a UA associate professor of geosciences.
Her team's continuous rainfall record shows a thousand-year period about 8,000 years ago when the Sahara became drier. That drier period coincides with when people left, she said.
"It looks like this thousand-year dry period caused people to leave," Tierney said.
"What's interesting is the people who came back after the dry period were different—most raised cattle. That dry period separates two different cultures. Our record provides a climate context for this change in occupation and lifestyle in the western Sahara."
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