FROM RAINOUT TO RAINSHADOW: A STABLE ISOTOPIC PERSPECTIVE OF THE CENTRAL ANATOLIAN PLATEAU

One of the major tasks in terrestrial paleoclimate research is the reconstruction of continental precipitation changes and its effect on vegetation patterns as well as animal and human environments. Stable isotopes in precipitation have become increasingly important for characterizing various effects of uplift related climate change and therefore allow us to investigate the relationship between climate and faunal and floral biodiversity over geological timescales. The central Anatolian plateau (Turkey) today -like its larger counterparts in Tibet and the Andes- creates a distinct rainfall pattern and reconstructing such patterns through geologic time is one of the major challenges for terrestrial paleoclimate research. With modern peak elevations of more than 3,000m the southern plateau margin (Taurus Mountains) must have played a pivotal role during surface uplift in controlling precipitation patterns within the plateau interior.

During 2008 - 2011 we sampled primarily springs and smaller catchment streams from the Taurus Mountains at the Mediterranean coast in the south over the Central Anatolian plateau to the Black Sea in the north. The aim of this study is to quantify the modern effect of orographic rainout of the Taurus Mountains on both δD and δ¹⁸O values as well as to provide insight into the combined effects of orographic rain out along the plateau margins and (evapo-)transpiration within the plateau interior.

Two δD and δ¹⁸O sampling transects on the southern flank of the Taurus Mountains show similar trends with a systematic decrease of δD (-18 ‰/km) and δ¹⁸O (-2.7 ‰/km) with increasing elevation. Samples taken north of the Taurus range have significantly lower δD and δ¹⁸O values compared to samples along the Mediterranean coast. However, increasing degrees of evaporation in the plateau interior systematically enriches lake, spring and stream waters in the D and ¹⁸O. Derived local meteoric waterlines (LMWL) of the two Taurus Mountain transects agree well with the Eastern Mediterranean Waterline (Gat & Carmi, 1970) which supports the idea that the local precipitation originated in the Eastern Mediterranean Sea. They contrast, however, those of the plateau interior that have slopes <8 (s ≈ 4.5) which is characteristic for waters that experienced strong evaporation.