Saudi Aramco World: May/June 2014 - page 22

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Saudi Aramco World
since Toumai lived here, the African Humid Period was only
the most recent of what may have been
hundreds
of wet phases.
The recent one is of interest today only because it affected ana-
tomically modern humans, and it is the one that may offer clues
about our own future.
Aahmat continues, “My family came out of the lake. I am the
offspring of that.”
His meaning: The lake gave his tribe life. But exactly when
that was is another question, perhaps one for science.
I
n 2010, Kröpelin teamed up with the Quaternary and
Paleoclimatology Group at the University of Köln,
directed by Martin Melles, whose work in lake sedi-
mentation analysis had nearly always taken him to
polar regions.
“You have virtually no opportunity in hot desert areas,” says
Melles. “The Sahara is as extreme and remote as Antarctica.”
Jens Karls, a doctoral student in paleoclimatology working
under Melles, undertook much of the operation of the corer,
which they set out in Lake Yoan. “You have a 30-kilogram [66-
lb] weight and a system with ropes. Then you have to pull it up
and let it drop again, and again. The upper sediments are very
easy to penetrate, but when you reach sediments that are a little
bit compact, then you have a coring speed of less than one mil-
limeter per hit,” he says.
One millimeter is less than a year’s sediment. The team went
down 16 meters (52½') in pursuit of layers from the dawn of
the Holocene Era. Through stroke after stroke of the corer’s
weight, in heat that, in sunshine on open water, often ap-
proached 50 degrees Centigrade (122° F), the team pressed on.
In the end, they reached their goal: a continuous, 10,940-year
“continental record of climate and environmental change.”
To understand “how our climate system worked in the past
and will operate in the future,” says Melles, “you need these geo-
logical archives widely distributed over the globe.” Having one
“representative core for the east Sahara is already a huge step.”
While analysis of the “long core” is still under way, says
Kröpelin, “we have indications of really global climate events,”
Men relax in morning shade at Lake Yoan, the largest of the Ounianga Kebir group. With its minimal reed cover and record-high evaporation
rate, the lake is saline. It is from this lake-bottom that in 2010 Kröpelin, Melles and Karls extracted the core sample, dating from the present
back to 10,940 years ago, that is still under study.
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