500,000 years of climate history stored year by year in Lake Van

500,000 years of climate history stored year by year in Lake Van

March 17, 2007, Saturday/ 20:15:00/ TODAY'S ZAMAN
Science Web site tells an interesting story of Turkey’s historical Lake Van. Long a center of Anatolian civilization, Lake Van is providing clues to a much deeper history and a uniquely precise insight into Eurasia’s climate history.“The bottom of Turkey’s Lake Van is covered by a layer of mud several hundreds of meters deep. For climatologists this unprepossessing slime is worth its weight in gold: summer by summer pollen has been deposited from times long past. From it they can detect right down to a specific year what climatic conditions prevailed at the time of the Neanderthals, for example. These archives may go back as much as half a million years.

“An international team of researchers headed by the University of Bonn now wants to tap this treasure. Preliminary investigations have been a complete success: the researchers were able to prove that the climate has occasionally changed quite suddenly -- sometimes within ten or twenty years.

“Every summer an inch-thick layer of lime - calcium carbonate - trickles down to find its final resting place at the bottom of Lake Van. Day by day during this period millions and millions of pollen grains float down to the depths. Together with lime they form a light-coloured layer of sediment, what is known as the summer sediment.

“In winter the continual ‘snowdrift’ beneath the surface changes its colour: now clay is the main ingredient in the sediment, which is deposited as a dark brown winter sediment on top of the pollen-lime mix. At a depth of 400 meters no storm or waves disturb this process. These ‘annual rings’ in the sediment can be traced back for hundreds of thousands of years. ‘In some places the layer of sediment is up to 400 meters thick,’ the Bonn palaeontologist Professor Thomas Litt explains. ‘There are about 20,000 annual strata to every 10 meters,’ he calculates. ‘We presume that the bottom of Lake Van stores the climate history of the last 800,000 years -- an incomparable treasure house of data which we want to tap for at least the last 500,000 years’. continues: “Professor Litt is the spokesman of an international consortium of scientists that wants to get stuck into a thorny problem: using high tech equipment they want to cut drill cores as thick as a man’s arm out of the lakebed sediment from a big floating platform - not an easy task at depths of 380 meters. The researchers want to drill down to a sediment depth of 250 meters. For this they have applied for funding by the International Continental Drilling Programme (ICDP). This would be the first time that an ICDP drilling was headed by a German.

“The prospects of this happening are not bad. A preliminary application was assessed as very good by the ICDP Executive Committee - above all thanks to a successful preliminary investigation which the researchers had carried out at Lake Van in 2004. The German Research Council (Deutsche Forschungsgemeinschaft, DFG) financed this. It has just extended the project for two more years.

“The sediment promises to deliver a host of exciting results. For example vulcanologists can determine exactly when volcanoes near the lake erupted. In this case there will suddenly be a black layer of ash between the annual layers. ‘With our test drill we counted 15 outbreaks in the past 20,000 years,’ Prof. Litt says. ‘The composition of the ash even reveals which nearby volcano it originates from.’”

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