The finding does not bode well for the region, according to
study researcher Steven Goldstein, a professor at the Lamont-Doherty
Earth Observatory at Columbia University. If the giant body of water
nearly vanished with no human pressures, what could be the consequences
with both man-made climate change and water diversions for irrigation that keep much of the resource from even reaching the Dead Sea?
"Without human intervention during the last interglacial, the run-off
declined or stopped," Goldstein said here Monday (Dec. 5) at the annual
meeting of the American Geophysical Union (AGU). Already, he said, water
has been a source of tension in the region.
With climate change, the Dead Sea region
is expected to become more arid, resulting in more pressure on water
resources. And recent signs suggest things are already happening; in
1930 the lake's surface was 1,280 feet (390 meters) below seal level,
dropping to 1,381 feet (421 m) below sea level in 2008 due to water
being used up by humans before it could even reach the lake, the
researchers said.
Disappearing sea
The Dead Sea
is the lowest continental point on Earth. With 33.7 percent salinity,
it's famous for the extra buoyancy swimmers get from its high salt
content. But the lake has shrunk and grown over the eons, and the new
study finds that those changes have occasionally been very extreme.
As part of the Dead Sea Deep Drill Core Project, Goldstein and other
colleagues drilled deep below the lakebed of the Dead Sea in 2010 and
2011 to pull up more than 1,300 feet (400 meters) of sediment in a long
column — a record of sediment deposits spanning 200,000 years.
The record captures nearly every season in that time period,
Goldstein said, with white layers of a mineral called aragonite marking
summer evaporations, when the minerals were left behind as water
vanished. Dark layers mark winter floods and sandstorms, which dump dark
silt into the lake. The silt then filters to the lake bottom, leaving a
record on the lakebed.
The researchers themselves witnessed both of these sorts of events live: At one point, they stood by as a flash flood washed dark sediment into the lake. On another day, a sandstorm with 100 mph (161 kph) winds disrupted their drilling.
Rock layers on the shore had already revealed that the lake has
fluctuated in size, filling the entire Jordan Rift Valley during the
last Ice Age. But the newly unearthed core showed that during the last
interglacial period, about 120,000 years ago, the lake dried up,
perhaps entirely. At that point,
Goldstein and his colleagues found a
layer of round beach pebbles on top of a 147-foot (45-m) layer of mostly
salt.
"It looks like the beach deposits that we see on the shore,"
Goldstein said. But this core was taken in what was then the center of
the lake basin.
The find means that at this time, in the warm period before the last
Ice Age, the Dead Sea dried up dramatically, leaving its salt behind —
"about how much salt we would expect if we were to take the Dead Sea
today [and] we were to evaporate it," Goldstein said.
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