Late glacial, Holocene and modern dinoflagellate cyst assemblages in the Aegean–Marmara–Black Sea corridor: statistical analysis and re-interpretation of the early Holocene Noah’s Flood hypothesis

Abstract

Understanding of the history of water exchange between the Mediterranean and Black seas has been hampered by the lack of continuous microfossil records for Holocene cores from the Marmara Sea Gateway (Aegean–Marmara–Black Sea corridor), and by the lack of core-top data linking modern microfossil assemblages with sea surface conditions. Based on molluscs, an abrupt transition from freshwater to marine conditions at ca. 7.5 ka has been postulated, with interpretation of this event as the basis for the story of Noah’s Flood. We have re-examined this hypothesis using organic-walled dinoflagellate cysts that show excellent preservation and moderate to high diversity in Pleistocene–Holocene sediments of the Marmara Sea Gateway. Principle component analysis of 16 core-top samples shows that an assemblage dominated by cysts of autotrophic gonyaulacoids distinguishes the hypersaline Aegean–Mediterranean water (salinity 31–38), whereas heterotrophic protoperidinioids characterise the low-salinity Marmara–Black Sea water (salinity ∼14–25). About 150 samples from eight cores, with multiple radiocarbon ages spanning the past ∼33 000 years, show correlatable major changes in cyst assemblages along the Marmara–Black Sea corridor. Variation in length and shape of gonyaulacoid species processes decreases upcore from basal units where there are no-analogue assemblages of cysts with highly variable spine development. It is shown that these variable and no-analogue assemblages correspond to brackish conditions (salinity ∼4–12) when calibrated against δ 18O data and salinity estimates derived from planktonic foraminifera. Salinity reconstructions indicate that the Aegean and Marmara seas were connected by ∼11 ka when the Marmara Sea was a brackish or low-salinity sea (∼12–17) and that the Black Sea was flowing into the Marmara Sea by at least 10.2–9.5 ka. There is no evidence to support either the idea that the Black Sea was a large freshwater lake suitable for farming in the early Holocene or that a sudden (<500-yr) flooding of the Black Sea by a 100-m-high waterfall of Mediterranean water occurred at 7.5 ka. It is shown that there is a need for precise use of salinity terms when reconstructing the history of saline lakes in the context of Neolithic human occupation so that the likelihood of agricultural settlement can be evaluated realistically.