The bottom of Turkeys Lake Van is covered by a layer of mud several hundreds of metres 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 metres 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 metres thick, the Bonn palaeontologist Professor Thomas Litt explains. There are about 20,000 annual strata to every 10 metres, 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.
250 metres of sediment = 500,000 years worth of climate archives