Climate changes in the Eastern Mediterranean over the last 5000 years and their links to the high-latitude atmospheric patterns and Asian monsoons

摘要

This research aims to improve the knowledge of the mid to late Holocene climate changes and the underlying drivers in the eastern Mediterranean. We focus on the Peloponnese peninsula, SW Greece, characterized by a W-E rainfall/temperature gradient and a strong climate-sensitivity to shifts in the large-scale atmospheric patterns. A radiocarbon-dated sediment core, taken from the ancient Lake Lema, a former lake in NE Peloponnese, was analyzed for distribution and hydrogen isotope (delta D) composition of n-alkanes and bulk organic geochemistry (delta C-13, TOC). The predominantly macrophyte (submerged/floating)-derived delta D-23 profile exhibits the largest long-term fluctuation in the record and co-varies with delta D of long-chain n-alkanes providing evidence for precipitation and temperature changes over the last 5000 years. The Lerna delta D-23 signal is sometimes in agreement with other n-alkane delta D records from SW Peloponnese indicating wetter conditions in the peninsula at ca 5000-4600, ca 4500-4100, ca 3000-2600 (more unstable in SW) and after ca 700 cal BP with drier periods at ca 4100-3900 and ca 1000-700 cal BP. Conversely, a NE-SW climate see-saw is revealed at ca 4600-4500, ca 3200, ca 2600-1800, and ca 1200-1000 cal BP when the delta D-23 Lerna exhibits more positive trends (drier in NE) with a reversal at ca 3900-3300, ca 3200-3000 and ca 1800-1300 cal BP. These opposing and sometimes similar signals between NE and SW Peloponnese can be explained by the relative dominance of high-latitude atmospheric patterns over the peninsula. A similar signal would be expected when the North Atlantic Oscillation (NAO) exerts the main control with NAO (+) creating conditions of reduced moisture. The dipole pattern is likely driven by shifts in North Sea-Caspian Atmospheric pattern (NCP), which account for the present-day regional climate variability with NCP (+) leading to wetter and colder conditions in NE Peloponnese. The Asian monsoonal system likely has an additional impact on the delta D variabilities through influencing the summer temperatures. There is a consistency between the Peloponnesian delta D signals and monsoonal records after ca 4000 cal BP confirming the actualistic models. Strong monsoonal periods coincide with cooler summers (lower delta D values) in Lerna, due to the northerly winds, the Etesians. On the contrary, SW Peloponnese is dominated by warmer conditions during the same periods as the area is located on the lee side of the mountain and highly influenced by the adiabatic warming associated with the subsidence over the Eastern Mediterranean.