Saudi Aramco World: May/June 2014 - page 20

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Saudi Aramco World
What lies under the waters of Lake Yoan
,
however, is what
may offer the Ouniangas’ greatest potential contribution to sci-
ence: “The long core.” Kröpelin speaks the term in a tone nor-
mally reserved for legends and elusive treasures.
For decades, Kröpelin had been looking at thousands of
now-dry paleolakes throughout Sudan, Egypt and Libya in his
search to reconstruct the environmental and climatological his-
tory of the eastern Sahara. His results were limited because all
the lakes dried up so long ago. ”We had nothing for the past
4000 years,” he says.
His hope was to find an ongoing accumulation of deposits,
something that is only possible in a present-day body of water.
In 1999, Kröpelin got to Lake Yoan, and he used a gravity
corer to excavate half a meter (1½') of lake-bottom sediment.
It was a test—and the find of a lifetime.
“There could have been nothing. It could have been sand.
It could have been homogenous mud where you couldn’t do
anything,” Kröpelin remembers. But it wasn’t. Clearly lay-
ered with sub-annual laminations, the core showed it was
possible to analyze its layers of deposits not just yearly, but
even seasonally.
“So it was clear this was worth a big coring campaign.”
He returned in 2004 to extract a 6.5-meter (21') core that
showed a continuous paleo-environmental record of the past
6000 years. Analysis of that long, thin column convinced Kröpe-
lin that the prevailing scientific understanding of the most con-
sequential African Holocene climate event—the demise of the
Green Sahara—“was wrong from the beginning.”
Citing analysis of pollen in the sediments of the core, in
a 2008 research paper Kröpelin challenged the hypothesis,
advanced by
deMenocal, that North Africa dried from savan-
nah to desert over the course of only a few centuries. The
new data, Kröpelin asserted, was evidence that it may have
been a far longer, much more gradual process, one taking not
centuries but millennia.
This is more than an academic question. Accuracy in Sa-
haran climate history research is important to today’s climate
modelers who believe that the better they “tune their models”
to history, the better they can project present-day climate
changes into the future.
Kröpelin’s analysis, comments deMenocal, is “extremely
important,” but geographically, he observes, it remains but a
single “data point.” In contrast, he says, “there are about 20
other different data points from West and East Africa, and
most recently in the Horn of Africa, that all look the same:
They all get abruptly drier after about 5000 years ago. So
which one was it? Or maybe it was both?” he adds. “To be
honest, I would say we don’t know yet.”
With reed-carpeted Lake Edem in Ounianga Serir in the background, sun-bleached and brown sandstone that once lay submerged offers samples
of fossil microorganisms that, when carbon-dated, yield evidence of the lake’s extent at different times.
Opposite:
Holding shells, souvenirs of the
African Humid Period from 11,000 to 5000 years ago, Fati Dadi of the office of tourism says she will string them into a necklace.
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