Late Holocene climate of the Eastern Mediterranean inferred from diatom analysis of annually-laminated lake sediments
Diatoms from the annually-laminated sediments of Nar crater lake in central Turkey are used to investigate climatic changes throughout the last 1720 years at decadal time resolution. A diatom-conductivity transfer function is employed to infer past water balance. Further information has been extracted from the palaeo-record through calculation of diatom biovolume, rarefaction (species diversity) and concentration, and through the identification of diatom bloom events in core thin sections. The Nar diatom sequence is compared with oxygen isotope (δ 18O) and pollen records from the same sediment cores in order to test the respective roles of changes in climate and land cover. Diatom-inferred (DI) conductivity excluding bloom taxa and δ 18O show very good correspondence for the first half of the record and demonstrate that this region experienced a period of century-scale drought prior to AD 540, with a subsequent rapid and simultaneous shift to fresher lake conditions and wetter climate. After a drier phase in the Nar record from AD 800-950, the period of the Medieval Climate Anomaly (AD 950-1400) was generally well watered. During the subsequent Little Ice Age (∼AD 1700-1900), DI-conductivity and δ 18O become decoupled. Thin sections reveal between 20 and 40 distinct diatom bloom events per century since AD 1100, with increasing frequency between AD 1700 and 2000. Human land-use changes evident in the pollen sequence may have influenced the diatom relationship with lake water conductivity in the later part of the record. None the less, diatom DCA axes do show a clear response to multi-decadal drought events within the last six centuries. Differences between the proxy-climate records from Nar Lake may be associated with the dissimilar thresholds to environmental fluctuations and non-stationarity in the response of different proxies through time. The palaeoclimate records from Nar show that arid periods occurred in the Eastern Mediterranean during the last two millennia that were more prolonged and extreme than those experienced in the last century.