Controversy surrounds reconnection of the Black Sea and Mediterranean during Holocene sea-level rise. This reconnection and its causes have implications for European and Middle Eastern archaeology, paleoclimate, and marine sedimentation; e.g., genesis of organic-rich muds (sapropels). Bill Ryan, Walter Pitman, and co-workers propose reconnection via a catastrophic flood of Mediterranean water into the Black Sea at ca. 7.5 ka, with speculation that this was the historical basis for the biblical story of Noah's Flood. In contrast, this paper suggests a more complex and progressive reconnection over the past 12 k.y. Today, the Black Sea exports considerably more brackish water than the saline inflow it receives from the Mediterranean. There is a stratified, two-layer flow that has a strong effect on aquatic life and seabed sediments. The "Marmara Sea Gateway" (narrow straits of Dardanelles and Bosphorus, and deep intervening Marmara Sea) provides a set of natural flow valves (and sediment traps) that in principle should contain a record of the reconnection. Using ~7500 line-km of seismic profiles, 65 soft-sediment cores, and 43 radiocarbon dates, we recognize a 10-11 k.y. history of low surface- water salinities in the Marmara Sea and northern Aegean Sea. The low-density surface layer promoted uninterrupted water-column stratification and depleted oxygen concentrations at depth and is attributed to persistent Black Sea outflow across the Bosphorus Strait. Seismic data reveal a climbing delta on the middle shelf south of the Bosphorus exit, active only from ca. 10 to 9 ka based on radiocarbon dating of its distal prodelta. The strength of the early outflow is confirmed by the progradation of this delta, and contemporaneous severe water-column stratification leading to deposition of sapropels in basinal areas. Ryan and Pitman's argument for a catastrophic Black Sea flood hinges on the rapid first appearance of euryhaline (Mediterranean) mollusks on Black Sea shelves at ca. 7.5 ka. In our view, this colonization was not a consequence of catastrophic flooding but rather the outcome of a slow establishment of two-way flow in the Bosphorus and a time lag during which the fresher waters of the deep Black Sea were replaced by more saline inflow, eventually allowing marine organisms to colonize the Black Sea shelves.
|Original language||English (US)|
|Number of pages||7|
|State||Published - 2002|
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