A six-hundred-thousand-year library
Lake Van is the largest lake in Turkey and the largest soda lake on Earth. Its water has a pH of 9.8, making it highly alkaline. The lake has no outlet, so everything that flows into it becomes trapped. About 600,000 years ago, a massive lava flow from the Nemrut volcano dammed the basin, creating this enormous endorheic lake. These conditions make Lake Van a perfect sediment trap. For millennia, fine particles have settled on the lakebed, forming distinct annual layers known as varves. These layers create a continuous record of geological and climatic history.
In 2010, the International Continental Scientific Drilling Program (ICDP) initiated the PALEOVAN project to access this archive. A team of scientists positioned a drilling barge over the deepest part of the lake, in water up to 360 meters deep. They extracted sediment cores reaching 220 meters below the lake floor, pulling up a continuous record that extends back more than 600,000 years. The total length of all recovered cores exceeded 800 meters. This single location provides the longest continuous continental climate record in the entire Near East.
Deciphering the archive
Each layer in the Lake Van cores records information about the world above. The sediment contains a detailed tephrostratigraphy, a timeline of volcanic ash. These ash layers are precise date markers for eruptions from the nearby Nemrut and Süphan volcanoes. Scientists can match the unique chemical signature of an ash layer to a specific eruption event.
Preserved pollen grains reveal the region's changing plant life. Layers containing high levels of tree pollen point to warmer, wetter interglacial periods when forests covered the Anatolian highlands. Layers dominated by grass and shrub pollen indicate cold, arid glacial periods when steppe environments were common. The cores document at least six full glacial-interglacial cycles. Geochemical analysis of the sediment also shows when the lake's water level dropped dramatically, sometimes by hundreds of meters, signaling periods of intense, prolonged drought. The varves themselves, which can be counted like tree rings in more recent sections of the core, provide a year-by-year account of environmental changes over the last 15,000 years.