Black Sea deluge hypothesis


The Black Sea deluge is the most well known of three hypothetical flood scenarios proposed for the Late Quaternary history of the Black Sea. It is one of the two of these flood scenarios which propose a rapid, even catastrophic, rise in sea level of the Black Sea during the Late Quaternary.

Black Sea deluge hypothesis

In 1997, William Ryan, Walter Pitman and their colleagues first published the Black Sea deluge hypothesis. They proposed that a catastrophic inflow of Mediterranean seawater into the Black Sea freshwater lake occurred at 7,150 14C years BP. Before that date, glacial meltwater had turned the Black and Caspian Seas into vast freshwater lakes draining into the Aegean Sea. As glaciers retreated, some of the rivers emptying into the Black Sea declined in volume and changed course to drain into the North Sea. The levels of the lakes dropped through evaporation, while changes in worldwide hydrology caused overall sea level to rise.
The rising Mediterranean finally spilled over a rocky sill at the Bosporus. The event flooded of land and significantly expanded the Black Sea shoreline to the north and west. According to these researchers, of water poured through each day, two hundred times the flow of Niagara Falls. The Bosporus valley roared and surged at full spate for at least three hundred days. They argued that the catastrophic inflow of seawater resulted from an abrupt sea-level jump that accompanied the Laurentide Ice Sheet collapse and the ensuing breach of a bedrock barrier in the Bosporus strait.
As proposed, the Early Holocene Black Sea flood scenario describes events that would have profoundly affected prehistoric settlement in eastern Europe and adjacent parts of Asia and possibly was the basis of oral history concerning Noah's flood. Some archaeologists support this theory as an explanation for the lack of Neolithic sites in northern Turkey. In 2003, Ryan and coauthors revised the dating of the early Holocene Noah's flood to 8,400 14C years BP.
Popular discussion of this Early Holocene Black Sea flood scenario was headlined in The New York Times in December 1996 and later published as a book.

Black Sea gradual inundation hypothesis

In addition to the early Holocene Noah’s Flood scenario proposed by William Ryan, Walter Pitman and their colleagues and the Caspian Sea overflow scenario of Chepalyga, the non-catastrophic progressive flood model has been proposed to explain the Late Quaternary sea level history of the Black Sea. For the progressive flood model, it is argued that as early as 11,000 or 10,000 BP, the level of the Black Sea rose above the shallowest sill depth of about in the Bosporus Strait and spilled into the Marmara Sea. At least for the first 1,000 years, this connection was a one-way outflow of the Black Sea into a very shallow Marmara Sea. At about 8,000 BP, the level of the Marmara Sea rose high enough such that a two-way flow started. The evidence used to support this scenario includes the disparate ages of sapropel deposition in the eastern Mediterranean Sea and Black Sea; buried backstepping barrier islands observed on the Black Sea shelf; and a sub-aqueous delta composed of Black Sea sediments in the Marmara Sea near the Bosporus Strait.

Late Pleistocene Great Flood hypothesis

In 2003 and 2007, a more ancient catastrophic flood scenario was proposed by Andrei L. Chepalyga for the Late Quaternary sea level rise of the Black Sea. The hypothesis for a Late Pleistocene Great Flood argues that brackish Neoeuxinian Lake, which occupied the Black Sea basin, was rapidly inundated by glacial meltwater overflow from the Caspian Sea via the Manych-Kerch Spillway shortly after the Late Glacial Maximum, about 17,000–14,000 BP. These extensive meltwater flooding events linked several lacustrine and marine water bodies, starting with the southern edge of the Scandinavian and southward, through spillways to the Manych-Kerch and Bosphorus, ultimately forming what has been referred to as the Cascade of Eurasian Basins. This event is argued to have caused a rapid, if not catastrophic rise in the level of the Black Sea. It might have imposed substantial stresses upon contemporary human populations and remained in cultural memory as the Great Flood. The authors also suggested that the event might have stimulated the beginning of shipping and horse domestication.

Controversy

The brief sensation caused by Ryan and Pitman has turned into an ongoing controversy. Critiques of the deluge hypothesis focus on the magnitude and pace of the water level rise. With enough moderation of these features, the catastrophe hypothesis is voided. However, a few key points should be noted:
Opponents of the deluge hypothesis point to clues that water has been flowing out of the Black Sea basin as late as 15,000 years ago. The local level must have been higher than the current-then-global level which had already risen from the last glacial minimum. In order to produce a Black Sea flooding such as the one described by Ryan and Pitman a solid obstruction of the Turkish Straits should have occurred. It must have had a significant height to allow for a rise on the south side, while to the north the water level should have been dropping. A notable point here is that the low lands in the Black Sea's basin would have already been flooded.
In this alternative scenario, much depends on the evolution of the Bosphorus. According to a study from 2001 the modern sill is below sea level, and consists of Quaternary sand over-lying Paleozoic bedrock in which three sills are found at below sea level. Sedimentation on these sills started before 10,000 years ago and continued until 5,300 years ago.
A large part of the academic geological community also continues to reject the idea that there could have been enough sustained long-term pressure by water from the Aegean to dig through a supposed isthmus at the present Bosphorus or enough of a difference in water levels between the two water basins.
In 2007, a research anthology on the topic was published which makes much of the earlier Russian research available in English for the first time and combines it with more recent scientific findings.
According to a 2009 study by Liviu Giosan,, and Stefan Constatinescu, the level in the Black Sea before the marine reconnection was below present sea level, rather than the, or lower, of the catastrophe theories. If the flood occurred at all, the sea level increase and the flooded area during the reconnection were significantly smaller than previously proposed. It also occurred earlier than initially surmised, 7400 BCE, rather than the originally proposed 5600 BCE. Since the depth of the Bosphorus, in its middle furrow, at present varies from, with an average depth of, a calculated Stone Age shoreline in the Black Sea lying lower than in the present day would imply that the contact with the Mediterranean might never have been broken during the Holocene, and hence there could have been no sudden waterfall-style transgression. An August 2009 article, based on this same study, reported that the flooding could have been "not so big".
A 2012 study based on process length variation of the dinoflagellate cyst Lingulodinium machaerophorum shows no evidence for catastrophic flooding.
A 2015 study reviewed the evidence accumulated and acknowledged a "fast transgression" lasting between 10 and 200 years..