Miracle in the Sahara: Oasis Sediments Archive Dramatic History, Part 1

Published on Spiegel Online International, by Johann Grolle, May 21, 2013 (Photo-Gallery).

A marvel of nature, the lakes of Ounianga in the Sahara Desert have lasted thousands of years and withstood dramatic climate change. Now, a German geologist has analyzed lakebed sediments to shed light on a spectacular chapter in human history.

“Water,” says Stefan Kröpelin, “water as far as the eye can see.” He is pointing to the south, where there is only one thing stretching to the horizon: sand, sand and more sand … //

… The Earth’s Archive:

Kröpelin first set up camp there more than 14 years ago. His goal was to recover sediments from the floor of the largest of the lakes, Lac Yoa, deposits that have formed in the lake’s roughly 11,000-year history.

These sediments are a unique archive of the history of the earth. They contain evidence of what is probably the most impressive and dramatic change in the climate occurring on the planet since the end of the last ice age. The mud on the lake floor tells the story of the greening of the biggest desert on earth, which then dried up a few millennia later.

Doing this kind of research in the middle of the Sahara is an adventure that requires stamina. Kröpelin has experienced it all — passport theft, a life-threatening schistosomiasis infection, sandstorms lasting for weeks — and yet the scientist remains undeterred. Even when local inhabitants turned up at his camp and threatened him, because they believed that his drilling activities were disturbing the virgin of the lake, he managed to appease them.

Every day, he and his team took a boat out to the raft they had anchored in the middle of Lac Yoa. Earlier, they had lowered a steel cylinder to the lake floor, at a depth of 25 meters. Now, using nothing but muscle strength, they rammed it deeper into the subsurface, millimeter by millimeter.

There was no canopy to provide protection from the fierce sun. One of the men would give the cylinder 30 to 40 blows with a 30-kilogram (66-pound) hammer before, dripping with sweat, handing it to the next man. Of course, they could only work when the wind, which sweeps across the flat desert from Libya, wasn’t constantly blowing fine sand into their eyes.

They drove the pipe 16 meters into the sediment before reaching the ice-age desert floor. The geologists had penetrated all the way to the original bottom of the lake.

After cutting it into one-meter segments and protecting it from impact and drying with a Plexiglas sleeve, the scientists took their prize out of the country. They traveled in a Toyota Land Cruiser across 1,200 kilometers of desert tracks to the capital N’Djamena. Then the drilling cores were sent to Cologne by airfreight.

There the experts were able to examine the clay-like deposits one layer at a time. The layers of mud were deposited on top of each other, not unlike tree rings, at an average rate of about a millimeter a year. Even in the desert, there are sufficient differences between the seasons to be clearly recognizable in the sediment.

History by the Layer: … //

… (full text).

Part 2: The Man of the Desert.


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