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Speranta-Maria Popescu, University Lyon 1 (France)
Oliver Bazeley, Cambridge University (United Kingdom)
Simona Boroi, University Lyon 1 (France)
Philippe Sorrel, Caen University (France)
Florant Dalesme, University Lyon 1 (France)
Gwenaël Jouannic, Université de Bretagne occidentale (France)
Martin Head, Brock University (Canada)
Gilles Lericollais, IGREMER (France)
Namik Çağatay, Istanbul Technical University (Turkey)
Jean-Pierre Suc, University Lyon 1 (France)
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The Late Glacial and Holocene were periods of important change in the Mediterranean region; both time intervals witnessed significant vegetation dynamics relating to changes in global climate and the transition from the Glacial to Holocene was characterised by a sea-level rise of 100 m. The eastern Mediterranean region (i.e. Marmara and Black Seas) was affected by major marine palaeoenvironmental changes induced by the invasion of marine Mediterranean waters at 12 ka and 8.4 ka, respectively into Marmara and Black Seas. Before this marine invasion, these two seas evolved as independent (perched) basins and were characterised by fresh- to brackish environments. What are the history and controlling factors of the connection between the Mediterranean, Marmara and Black Seas? Was the invasion a progressive or catastrophic event?
To answer at these questions, a high-resolution palynological study (pollen and dinoflagellates cysts) was performed on 40 surface-samples and five cores (four on the Black Sea and one in the Marmara Sea). Studies on the pollen transport and taphonomy show that the pollen concentration in surface sediment samples is linked to pollen density, climate and location of the studied core (i.e. proximal/ distal). Generally, high sea-levels correspond to warmer periods and the surface sediment samples are characterized by high percentages of mesophilous (i.e. warm-temperate) trees. On contrary, cooler periods (low sea-levels) are characterised by high percentages of herbs. Bisaccate pollen grains, especially those of Pinus, have high buoyancy and therefore can float on surface waters for some years and as a consequence, become widely dispersed.
The high-resolution sampling strategy ensures the identification of climate and sea-level changes during the last 20 kyrs. Three main pollen ratios can be used as climatic and eustatic indexes: 1. mesophilous trees / Artemisia ratio, which correlates well with the GRIP oxygen isotope curve, 2. Pinus / halophytes ratio, which documents on the distal or proximal location of the core in relation to sea-level changes, 3. halophytes / herbs ratio has the same significance as the previous ratio, but it is continuously applicable, even within sapropels Two dinocysts assemblages have been identified, with the marine assemblages overlaying brackish endemic assemblages. The marine assemblages are composed of both stenohaline and euryhaline species, whereas the brackish assemblages feature exclusively stenohaline species. The hydrographic impact of the marine transgression is complex and the ecological dynamics reflect this complexity. The initial ecological change is characterised by a rapid expansion of marine euryhaline species populations with a subsequent, but more gradual expansion of stenohaline species populations. This dynamic could reflect the dramatic initial impact of the transgression coupled with the progressive hydrographic stabilisation of the basins.
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