The tempo of Holocene climatic change in the eastern Mediterranean region: new high-resolution crater-lake sediment data from central Turkey

Abstract

This study presents results from a multi-proxy analysis of cores taken in a crater-lake sequence from Eski Acigöl in centr-al Turkey which cover the period from pre-c. 16000 cal. yr BP to the present. The sediments comprise an upper unit of enerally non-laminated, banded to massive silts and peats of mid- to late-Holocene age, overlying a laminated unit of late-Pleistocene to early/mid-Holocenie age. The laminae, comprising mainly aragonite. amorphous silica (diatom frustules) and organic matter were formed in a relatively deep, dilute. meromictic lake. Pollen data indicate an abrupt replacement of Arteyisia-chenopod steppe by grass-oak-terebinth parkland during the period of laminae deposition, marking the start of the Holocene. A gradual increase in tree pollen during the early Holocene came to an end c. 6500 cal. yr BP (U-series and adjusted 14 C timescale), when mesic deciduots taxa declined at the same time as lake levels fell. Human impact on regional vegetation is inferred from a sharp decline in oak around 4500-4000 cal. yr BP. Diatom, isotopic and mineralogical data indicate that during the second half of the Holocene the lake became relatively shallow and oscillated between fresh and brackish/evaporated water conditions. The contrast between wetter early and drier late-Holocene climatic conditions is matched by other eastern and central Mediterranean proxy climate data. While the Eski Acigöl sequence resembles Holocene hydroclimatic changes in the Saharo-Arabian zone and was also apparenitly linlked to orbital forcing, it is unlikely to have had the samlle direct cause, i.e., an expansion and subsequent retreat of monsoon rainfall.