The biostratigraphy, palaeoecology and geochemistry of a long lacustrine sequence from NW Greece
Examination of an important new 319m core of lake sediment recovered from Ioannina in NW Greece has attempted to relate changes in the lake to variations in the regional climate of south-central Europe over the last 600,000 years. The site is known to have been extremely sensitive to past climatic change for three reasons: (i) temperate vegetation persisted throughout glacial stages (albeit at low frequencies), so the vegetational response to climatic change would therefore have been almost immediate; (ii) the extreme thickness of the sediments suggests that accumulation rates were high (at times, > 1m per thousand years), which has enabled high-resolution palaeoclimatic reconstructions; and (iii) precipitation of authigenic carbonate has preserved a remarkably sensitive proxy record of productivity variations for most of the lake's history. Well-defined shifts from glacial - interglacial mode have been correlated with vegetational changes identified in a core previously analysed from the same basin (using magnetic susceptibility profiles), enabling tentative correlations to be suggested with other European terrestrial sequences and with the marine oxygen isotope record, back to marine isotope stage 16. Twelve AMS radiocarbon determinations from the upper part of the core, together with the identification of a series of reversed palaeomagnetic events within the Brunhes chron, support the proposed age model for the sequence. The sediments at Ioannina, unlike most of the other long terrestrial European sequences, are calcareous and contain mollusc and ostracod assemblages. Part of this project has involved a comprehensive review of Quaternary and modem aquatic faunas from the lake, as well as the description, illustration and critical assessment of several poorly-known endemic taxa. Faunal assemblage data have been used to provide valuable information concerning the variable response of lake-level to climatic change over time. Convincing new mollusc an evidence indicates low lake-levels at the Last Glacial Maximum, agreeing with regional pollen data, but conflicting with geomorphological evidence derived from Kastritsa, a well-documented nearby Palaeolithic cave site. It is suggested that this discrepancy may be a result of subsequent tectonic uplift of the rockshelter. In addition, stable isotopic analyses of both the ostracods and the bulk carbonate within the sediments have contributed towards deriving a comprehensive palaeoenvironmental history for the site. Although the study analysed physical, biological and geochemical aspects of the entire core, two distinct parts of the record were selected for more detailed investigation. High-resolution analysis over the last interglacial (the Eemian) has revealed evidence for a clear, two-step deglaciation at the beginning of the period, known from elsewhere as the Zeifen-Kattegat Oscillation. Climatic instability has also been detected within the full interglacial. Comparisons are drawn with a range of other Eemian records from across Europe, as well as the Greenland ice cores. High-resolution analysis of the period from the end of the last glacial to the present day has also revealed evidence for climatic instability. A cool and arid oscillation is demonstrated by several climatic proxies that may constitute the first recognition of the Younger Dryas stadial from Greece. A shorter, but more subdued cooling event has also been detected during the first half of the Holocene, which may correspond with a widespread climatic oscillation from high-resolution terrestrial, marine and ice core records that has been dated to between 7,500 and 8,000 years BP.
Palaeoecology, Quaternary Science, NW Greece, Ioannina, Lake sediments, Biostratigraphy, Fresh-water molluscs, Fresh-water ostracods, Stable isotopes
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