Third Millennium BC Climate Change and Old World Collapse

Volume 49 of the series NATO ASI Series pp 653-678

δ18o and Trace Element Measurements as Proxy for the Reconstruction of Climate Changes at Lake Van (Turkey): Preliminary Results

  • Gerry LemckeAffiliated withEAWAG, Swiss Federal Institute for Environmental Science and Technology
  • , Michael SturmAffiliated withEAWAG, Swiss Federal Institute for Environmental Science and Technology

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The sediments of Lake Van, the fourth largest terminal lake on earth, located at the eastern end of the Taurus Mountain Range show an undisturbed continuous record of chemically precipitated carbonate varves, which provide:

a, a yearly carrier for changes in environmental proxy like δ18O, Sr/Caand Mg/Ca of authochthonous precipitated carbonates which allow to detect short term climatic variations,

b, a continuous, non floating varve chronology back to 13,700±356 yrs BP.

Calculations based on an isotopic-hydrologic balance model show that temperature fluctuations are less important for the isotope enrichment in Lake Van than changes of the relative humidity. Thus a paleohumidity curve of Lake Van can be estimated and compared to a Mg/Ca record which is found to be a proxy for lake salinity.

Lake Van sediments indicate a first period of cold and arid climate between 12,600–10,460 yrs BP. During this time humidity decreased by 0.17 or 30% (no temperature shift) or 20%, if temperature is reduced by 5 °C.

A second phase of climatic change also occurred: in a first period (4,190–3,040yrs B.P.), slightly reduction in lake level and humidity mark a regional climate shift toward more continental climate with reduced precipitation. In a second period (3,040– 2,000 yrs B.P.), precipitation increased again, but humidity remained at a level reduced 5% below that encountered today.