Danube Delta Holds Answers To ‘Noah’s Flood’ Debate
ScienceDaily (Jan. 22, 2009) –
Did a catastrophic flood of biblical proportions drown the shores of
the Black Sea 9,500 years ago, wiping out early Neolithic settlements
around its perimeter? A geologist with the Woods Hole Oceanographic
Institution (WHOI)and two Romanian colleagues report in the January
issue of Quaternary Science Reviews that, if the flood occurred at
all, it was much smaller than previously proposed by other
researchers.
Using sediment cores from the delta of the Danube River, which empties
into the Black Sea, the researchers determined sea level was
approximately 30 meters below present levels-rather than the 80 meters
others hypothesized. `We don’t see evidence for a catastrophic flood
as others have described,’ said Liviu Giosan, a geologist in the WHOI
Geology and Geophysics Department.
Ten thousand years ago, at the end of the last glacial period, the
Black Sea was a lake-cut off from the Sea of Marmara and beyond it the
Mediterranean by the Bosphorus sill. Debate in geological and
archaeological circles has focused on whether, as glaciers melted and
global sea levels began to rise, the Bosphorus sill overflowed
gradually or whether a flood broke through the sill, drowning some
70,000 square kilometers and wiping out early Neolithic civilizations
in the region. In addition to questions about the rate of the flood,
investigators continue to debate the extent of the flood — a debate
centered around what the level of the Black Sea was 9,500 years ago.
In the late 1990s, Columbia University researchers Bill Ryan and
Walter Pitman examined the geological evidence and estimated the Black
Sea level at the time of the flood was approximately 80 meters lower
than present day levels.
They suggested that the impact of a Black Sea flood could have forced
the movement of early agriculturist groups to central Europe and
established the story of Noah and his ark, as well as flood myths
among other peoples.
The source of the uncertainty fueling the Black Sea flood debate is
the difficulty of finding reliable sea level markers to date the
flood. `Sea level is like the Holy Grail,’ said Giosan. `You can’t
really talk about a flood if you don’t know the exact levels of the
sea level in both the Black Sea and outside it in the
Mediterranean. And that’s what we tried to find.’
Scientists examine the geochemistry of sedimentary deposits for
evidence of fresh water fauna and the morphology of features on the
seafloor, trying to infer drowned beaches or wind-generated dunes, but
there are pitfalls associated with these indicators. Sediments are
subject to erosion by waves and currents, and sand deposits formed by
underwater currents can misleadinglybe interpreted as dunes or
beaches. `Instead, what we use as indicators of sea level is the level
of the Danube River delta plain, an immense landform that cannot be
mistaken for something else,’ Giosan stated.
A delta is formed when a river empties into a body of water. It dumps
sediments and builds a flat plain-the delta-that is within a couple of
meters of the shore and is, therefore, an indicator of sea level. In
2006, a team ledby Liviu Giosan showed that contrary to Soviet-era
data suggesting large oscillations of Black Sea level, the development
phases of the Danube delta demonstrate that the level was more or less
as today in the last 6000 years.
To extend their record back in time beyond 6000 years, in 2007, Giosan
and his colleagues drilled a new core to 42 meters depth at the mouth
of the Danube River, the largest river emptying into the Black
Sea. Their goal was to reconstruct the history of that part of the
delta-before and after the flood- through an examination of the
sediments. In analyzing the delta sediment from the new core as well
as others taken in the region, Giosan’s team discovered fresh water
deposits of the newly forming delta dating back approximately 10,000
years, subsequently overlaid by fine marine sediments, followed by the
modern delta deposits.
`It’s amazing,’ said Giosan. `The early delta was forming in a fresh
water lake just a couple of hundred years before the flood. And after
the flood you have these marine deposits overlaying the whole delta
region.’
Using sediment cores to reconstruct the delta with accurate dates is
challenging. To attach a date to the layers of a core, scientists use
radiocarbon dating on the fossil shells of animals found in the
core-for instance, clams or snails. But in energetic areas, waves can
erode sediment on the seabed and heave up older shells, depositing
them in `younger’ sediments. To address these concerns, Giosan and his
team used an approach that had not been used before in the Black
Sea. They employed high resolution dating performed at WHOI’s
Accelerator Mass Spectrometer (AMS) facility and only used
`articulated’ bivalves – those where both sides of the shell were
still attached as they are when alive. The shells are held together by
an organic substance that degrades easily when they are dead, so the
valves usually separate when the animal dies. When bivalves are found
intact, it means they were not moved by waves and they are likely to
be in situ.
Once the researchers dated and reconstructed the delta plain, they
could determine sea level for the Black Sea. They found that the Black
Sea level at the time of the flood was around 30 meters below present
levels. Determining how much water poured over the Bosphorus sill
remains problematic. There is no direct reconstruction of the sea
level for the Marmara, but, according to Giosan, indirect methods put
it at approximately 5 to 10 meters above the Black Sea level at the
time of the flood.
`So if this is true, it means that the magnitude of the Black Sea
flood was 5 or 10 meters but not 50 to 60 meters,’ said
Giosan. `Still, having flooded the Black Sea by 5 meters can have
important effects, for example, drowning of the Danube Delta and
putting an area of 2,000 square kilometers of prime agricultural land
underwater. This has important implications for the archaeology and
anthropology of southern Europe, as well as on our understanding of
how the unique environment of the Black Sea formed.’
Funding for this project was provided by the WHOI Coastal Ocean
Institute. Adapted from materials provided by _Woods Hole
Oceanographic Institution_ () .