LATE QUATERNARY GLACIATION AND PALEOCLIMATE OF TURKEY INFERRED FROM COSMOGENIC 36Cl DATING OF MORAINES AND GLACIER MODELING

摘要

The main objective of this dissertation is to improve the knowledge of glacial chronology and paleoclimate of Turkey during the Late Quaternary. The 36Cl cosmogenic exposure ages of moraines show that Last Glacial Maximum (LGM) glaciers were the most extensive ones in Turkey in the last 22 ka (ka=thousands years), and they were closely correlated with the global LGM chron (between 19±23 ka). LGM glaciers started retreating 21.3±0.9 ka (1σ) ago on Mount Erciyes, central Turkey, and 20.4±1.3 ka ago on Mount Sandiras, southwest Turkey. Glaciers readvanced and retreated by 14.6±1.2 ka ago (Late Glacial) on Mount Erciyes and 16.2±0.5 ka ago on Mount Sandiras. Large Early Holocene glaciers were active in Aladaglar, south-central Turkey, where they culminated at 10.2±0.2 ka and retreated by 8.6±0.3 ka, and on Mount Erciyes, where they retreated by 9.3±0.5 ka. The latest glacial advance took place 3.8±0.4 ka ago on Mount Erciyes. Using glacier modeling together with paleoclimate proxy data from the region, I reconstructed the paleoclimate at these four discrete times. The results show that LGM climate was 8-11oC colder than today (obtained from paleotemperature proxies) and wetter (up to 2 times) on the southwestern mountains, drier (by ~60%) on the northeastern ones and approximately the same as today in the interior regions. The intense LGM precipitation over the mountains along the northern Mediterranean coast was produced by unstable atmospheric conditions due to the anomalously steep vertical temperature gradients on the Eastern Mediterranean Sea. In contrast, drier conditions along the southern Black Sea coast were produced by the partially ceased moisture take-up from the cold or frozen Black Sea and prevailing periglacial conditions due to the cold air carried from northern hemisphere's ice sheets. Relatively warmer and moister air from the south and overlying cold and dry air pooled over the northern and interior uplands created a boundary between the wet and dry LGM climates somewhere on the Anatolian Plateau. The analysis of Late Glacial advances suggests that the climate was colder by 4.5-6.4oC based on up to 1.5 times wetter conditions. The Early Holocene was 2.1oC to 4.9oC colder on Mount Erciyes and up to 9oC colder on Aladaglar, based on twice as wet as today's conditions. The Late Holocene was 2.4-3oC colder than today and the precipitation amounts approached the modern levels. Glaciers present on Turkish mountains today are retreating at accelerating rates and historical observations of the retreat are consistent with the behavior of other glaciers around the world.