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Under the Dead Sea, warnings of dire drought

ScienceDaily (March 22, 2017)

Titre : Under the Dead Sea, warnings of dire drought

Ancient sediments tell a story that could be repeated

ScienceDaily (March 22, 2017)
Nearly 1,000 feet below the bed of the Dead Sea, scientists have found evidence that during past warm periods, the Mideast has suffered drought on scales never recorded by humans — a possible warning for current times. Thick layers of crystalline salt show that rainfall plummeted to as little as a fifth of modern levels some 120,000 years ago, and again about 10,000 years ago. Today, the region is drying again as climate warms, and scientists say it will get worse. The new findings may cause them to rethink how much worse, in this already thirsty and volatile part of the world

The landlocked Dead Sea, straddling Israel, Jordan and Palestinian lands, is earth’s lowest spot on land. Its current shoreline lies about 1,300 feet below sea level, and its floor extends down another 900 feet. Fed mainly by the Jordan River drainage, which extends also into Syria and Lebanon, it is a dead end for water, and so is extremely salty ; its Biblical name in Hebrew is Y ?m ha-Melah, the sea of salt. In recent years, its level has dropped about four feet a year. But hot, dry weather is not the main cause yet ; rather, booming populations in the region need more water than ever, and people are sucking so much from the watershed, very little reaches the Dead Sea, where evaporation is outweighing input. The U.N. Food and Agriculture Organization estimates that much of the region already has per capita water availability only a tenth of the world average. Rainfall has declined about 10 percent since 1950, and existing climate models say it could sink another 20 percent this century, even as population continues to grow. Israel is meeting demand by desalinating Mediterranean seawater, but poorer, landlocked Jordan and the Palestinian territories are desperate for more. In adjoining Syria, a record 1998-2012 drought likely stoked by climate change is believed to have helped spark the ongoing civil war, which has now claimed more than 500,000 lives and infected neighboring nations. In 2010, scientists from a half-dozen nations drilled 1,500 feet into the deepest part of the seabed, bringing up a cross section of deposits recording 200,000 years of regional climate history — the longest such archive in the Mideast. (Around-the-clock drilling went for 40 days and 40 nights — perhaps a respectful bow to the rainfall of the Biblical Flood.) The cores revealed alternating layers of mud washed in with runoff during wet times, and crystallized salt, precipitated out during dry times when the water receded. This instantly made it clear that the region has suffered epic dry periods, but the core was not analyzed in great detail until now. The new study shows that the salt accumulated rapidly ?an estimated half-inch per year in many cases. The researchers spotted two striking periods. About halfway down they found salty layers some 300 feet thick, indicating a long-term drop below the sea’s current level. This came in a period between ice ages, 115,000 to 130,000 years ago, when variations in Earth’s orbit brought temperatures about 4 degrees hotter those of the 20th century ?equivalent to what is projected for the end of the 21st century. The lake refilled when glaciers readvanced in sub-polar regions and the Mideast climate cooled and became moister. The cores show a similar drop in lake level just 6,000 to 10,000 years ago, following the most recent ice age, when temperatures were probably a bit cooler than now.

Story Source  : Lamont-Doherty Earth Observatory, Columbia University.

Annonce (ScienceDaily)

Page publiée le 19 janvier 2018