Holocene environmental and climate change in the southern Levant: diatom-based palaeolimnology of Lake Kinneret (Israel)

Abstract

The Eastern Mediterranean and especially the southern Levant are key regions for palaeoclimatological and palaeoenvironmental research due to their highly complex topography and climatic variabilty. Nevertheless, our knowledge and understanding of Holocene environmental variability and its possible drivers is still limited. Diatoms have a well-recognised potential to generate high-quality palaeolimnological data because they are often well preserved in lacustrine sediment records, which provide excellent high-resolution terrestrial palaeoarchives. To date, there has been surprising little Quaternary diatom research across the circum-Mediterranean, and the southern Levant in particular.<br /> Therefore, this PhD thesis aimed to investigate and understand the potential of diatoms as palaeoenvironmental and palaeoclimate indicators in Eastern Mediterranean Quaternary research. Diatom death assemblages were analysed from modern sediment surface samples and, for palaeoenvironmental reconstruction, from an 18 m long sediment sequence recovered from Lake Kinneret (Israel) in 2010, covering the last 9,000 cal yrs BP. As part of the investigation, the formal description of a new diatom species, Cyclotella paleo-ocellata VOSSEL AND VAN DE VIJVER found in the lake sediment core was achieved, adding a taxonomic focus to the research.<br /> This thesis provides a high-resolution diatom dataset for Lake Kinneret based on a robust chronology for the Holocene, which is unique in the southern Levant region. The results confirm that diatoms provide a powerful tool for Holocene palaeoenvironmental and climatological reconstructions in the southern Levant region, especially if they are interpreted in combination with multi-proxy datasets. The diatom data revealed the palaeolimnological history of Lake Kinneret for the past 9,000 cal yrs PB, i.e. changes in lake level and therefore regional climate variability. Our results show that the Early Holocene was characterised by fluctuating lake levels, which are linked to alternations between arid and more humid climate conditions at Lake Kinneret. Diatoms indicated a prolonged stable deep lake phase throughout the mid-Holocene and the onset of the Late Holocene due to long-lasting humid climate, which was possibly interrupted by smaller drought events (declined lake levels) occurring at around 4,600 and 3,600 cal yrs BP. During the Late Holocene, the diatom record indicates the initiation and subsequent pattern of anthropogenic impact on the lake's ecosystem by changing its trophic status from an oligotrophic to a meso-eutrophic system at around 2,200 cal yrs BP until present. Shifts in lake levels and the climate signal can therefore not be derived from the diatom dataset for this time.<br /> The comparison between lake-level reconstructions from Lake Kinneret (based on the provided diatom data in this thesis) and the Dead Sea record indicates a close interaction between both lake systems as they seem to react in similar ways to major hydrological changes in the catchment, e.g. due to Holocene rapid climate changes.<br /> Our investigations emphasize the need for further analysis of long, terrestrial diatom records with robust age-control in the southern Levant and the circum Mediterranean region. Moreover, more modern analogue studies from lakes, which are used for palaeoenvironmental reconstructions, would be very useful, improve calibration and interpretation of fossil datasets.