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 occurred 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 7,200 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 155,000 km2 (60,000 sq mi) of land and significantly expanded the Black Sea shoreline to the north and west. According to the researchers, "40 km3 (10 cu mi) 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 period sites in northern Turkey. In 2003, Ryan and coauthors revised the dating of the Early Holocene Noah’s Flood to 8,400 BP.
Popular discussion of the Early Holocene Black Sea flood scenario proposed by William Ryan, Walter Pitman and their colleagues was headlined in The New York Times in December 1996. and later published as a book.
Late Pleistocene Great Flood hypothesis
In 2003 and 2007, a different catastrophic flood scenario was proposed for the Late Quaternary sea level rise of the Black Sea. The hypothesis for their 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. Theoretically, it would 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.
Gradual inundation of Black Sea 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 proposed by Andrei L. Chepalyga, the non-catastrophic progressive flood model (or gradual inflow 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 30 m (98 ft) 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.
The brief sensation caused by Ryan and Pitman has turned into an ongoing controversy. Critiques of the deluge hypothesis focus on the magnitude or the pace of the water level rise or both. With enough blurring of these features the hypothesis is voided. However, a few key points should be noted:
- Since the ending of the last glacial period the global sea level has risen some 120 m (390 ft). The process took approximately 10,000 years and abated about 7,600 years ago.
- The flood hypothesis hinges on the geomorphology of the Bosphorus since the end of the glacial age. The Black Sea area has been sealed off and reconnected numerous times during the last 500,000 years.
- Various methods have been used to study and date (e.g., sea floor drillings, radiocarbon dating, biological markers) the recent evolution of the Black Sea. The heterogeneous data do not fit into a neat frame, which precludes the confirmation for a sharply defined event.
- The Black Sea flood hypothesis concerns an event supposed to have occurred during the last 10,000–12,000 years with the water level rising rapidly enough to cause easily noticeable effects.
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 32–34 m (105–112 ft) below sea level, and consists of Quaternary sand over-lying Paleozoic bedrock in which three sills are found at 80–85 m (260–280 ft) 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 (if at all) between the two water basins.
According to a 2009 study by Liviu Giosan, Florin Filip, and Stefan Constatinescu, the level in the Black Sea before the marine reconnection was 30 m (100 ft) below present sea level, rather than the 80 m (260 ft), 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, c. 7400 BCE, rather than the originally proposed 5600 BCE. Since the depth of the Bosphorus, in its middle furrow, at present varies from 36 to 124 m (118 to 407 ft), with an average depth of 65 m (213 ft), a calculated stone age shoreline in the Black Sea lying 30 m (100 ft) 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.
A 2012 study based on process length variation of the dinoflagellate cyst Lingulodinium machaerophorum shows no evidence for catastrophic flooding.
A 2016 study reviewed the evidence accumulated and reaffirmed the catastrophic scenario (Project: DO02-337 "Ancient coastlines of the Black Sea and conditions for human presence", sponsored by Bulgarian Scientific Fund).
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