TEMPERATURE ESTIMATES AND HYDROCLIMATE VARIABILITY IN CORRESPONDENCE TO DANSGAARD-OESCHGER EVENTS AND GLACIAL TERMINATIONS FROM THE EASTERN MEDITERRANEAN

Lacustrine records from deep closed lakes, such as the 600,000 yrs-old sedimentary sequence from Lake Van (Turkey), can provide detailed insights into the mechanisms of past environmental changes in the continental interior. The record is continues and has an excellent age control over the last 150 kyrs. Repetitive intervals of annually-laminated sections are reflected in a sub-annual resolved color record. The color record documents lake-level rises for all Dansgaard-Oeschger interstadials as represented by the δ¹⁸O record of Greenland ice reflecting temperature increases. Comparison with model hindcasts from LOVECLIM experiments, supports the notion that the lake-level increases during the warm interstadials is caused by precipitation increases due to atmospheric changes as consequence of AMOC increase during a paucity of ice-sheet calving events.

Reconstructed magnitudes of temperature and precipitation changes in the Eastern Mediterranean are unknown over the last 150 kyrs although it covers a critical time and area in human and mammal evolution. We quantified temperature and hydroclimate changes within a multi-proxy biomarker study. Lipid biomarkers during several D-O events from MIS 3 and over the last two terminations were extracted at centennial resolution. Mean air temperatures (MAT) based on down-core distributional changes in branched glycerol dialkyl glycerol tetraethers (brGDGTs), indicate a 1.5-3° warming at stadial/interstadial transitions and 2-4° warming for glacials/interglacial transitions. Simultaneous analysis of the leaf wax hydrogen isotopic composition (δ²H_wax) result in a reconstruction of changes in the source water due to variable precipitation/evaporation ratio. Isotopically 10 ‰ (20 ‰) lighter dD-values of leaf-wax n-alkane C₂₉ argue for a significantly increased humidity during the interstadials (interglacials) compared to the stadials (glacials). Recently, it has been proposed that highly variable climates, substantially influenced megafaunal transition events instead of the more often proposed effect of long-lasting glacial coldness. How far, the changes in magnitude of the reconstructed temperatures and precipitation in the Eastern Mediterranean fit into the proposed climate-driven mechanism of megafaunal evolution needs to be tested.