The Black Sea is bounded by Europe and Asia. It has an area of 436,400 km2 and connects to the Mediterranean Sea via the Sea of Marmara and the Aegean Sea. The Black Sea receives freshwater from large Eurasian rivers like the Danube, Dnieper, and Don. It is the world's largest meromictic basin, with anoxic deep waters not mixing with oxygenated surface waters. The Black Sea supports a diverse marine ecosystem adapted to its brackish nutrient-rich waters.

1. BLACK SEA By Sima Elenis

2. • The Black Sea is bounded by Europe, Anatolia and
the Caucasus and is ultimately connected to the Atlantic Ocean via
the Mediterranean and the Aegean seas and various straits.
The Bosphorus strait connects it to the Sea of Marmara, and the
strait of the Dardanelles connects that sea to the Aegean Sea region
of the Mediterranean. These waters separate eastern
Europe and western Asia. The Black Sea is also connecte to the Sea
of Azov by the Strait of Kerch.

3. • The Black Sea has an area of 436,400 km2 (168,500
sq mi) (not including the Sea of Azov), a maximum
depth of 2,212 m (7,257 ft), and a volume of 547,000
km3.The Black Sea forms in an east-west trending
elliptical depression which lies
between Bulgaria, Georgia, Romania, Russia, Turkey
, and Ukraine. It is constrained by the Pontic
Mountains to the south, the Caucasus Mountains to
the east and features a wide shelf to the northwest.
The longest east-west extent is about 1,175 km.

4. • The Black Sea has a positive water balance; that
is, a net outflow of water 300 km3 per year
through the Bosphorus and the Dardanelles into
the Aegean Sea. Mediterranean water flows into
the Black Sea as part of a two-way hydrological
exchange. The Black Sea outflow is cooler and
less saline, and floats over the warm, more
saline Mediterranean inflow -because of density
difference due to salinity-, leading to a
significant anoxic layer well below the surface
waters. The Black Sea also receives river water
from large Eurasian fluvial systems to the north
of the Sea, of which
the Don, Dnieper and Danube are the most
significant.

5. Geology and bathymetry
• The modern basin is divided into two sub-basins by a
convexity extending south from the Crimean Peninsula. The
large shelf to the north of the basin is up to 190 km wide, and
features a shallow apron with gradients between 1:40 and
1:1000. The southern edge around Turkey and the western
edge around Georgia, however, are typified by a narrow shelf
that rarely exceeds 20 km in width and a steep apron that is
typically 1:40 gradient with numerous submarine canyons and
channel extensions. The Euxine abyssal plain in the centre of
the Black Sea reaches a maximum depth of 2,212 m
(7,257.22 ft) just south of Yalta on the Crimean Peninsula.
The littoral zone of the Black Sea is often referred to as the Pontic littoral.

6. Hydrology and hydrochemistry
• The Black Sea is the world’s largest meromictic basin where
the deep waters do not mix with the upper layers
of water that receive oxygen from the atmosphere. As a
result, over 90% of the deeper Black Sea volume is anoxic
water. The current hydrochemical configuration is primarily
controlled by basin topography and fluvial inputs, which
result in a strongly stratified vertical structure and a positive
water balance. The upper layers are generally cooler, less
dense and less salty than the deeper waters, as they are fed
by large fluvial systems, whereas the deep waters originate
from the warm, salty waters of the Mediterranean. This
influx of dense water from Mediterranean is balanced by an
outflow of fresher Black Sea surface-water into the Marmara
Sea, maintaining the stratification and salinity levels.

7. • The Black Sea supports an active and dynamic marine
Ecology ecosystem, dominated by species suited to the brackish,
nutrient-rich, conditions. As with all marine food webs, the
Black Sea features a range of trophic groups,
with autotrophic algae, includingdiatoms and dinoflagellates,
acting as primary producers. The fluvial systems draining
Eurasia and central Europe introduce large volumes of sediment
and dissolved nutrients into the Black Sea, but distribution of
these nutrients is controlled by the degree of physiochemical
stratification, which is, in turn, dictated by seasonal
physiographic development. During winter, strong wind
promotes convective overturning and upwelling of nutrients,
while high summer temperatures result in a marked vertical
stratification and a warm, shallow mixed layer. Day length
and insolation intensity also controls the extent of the photic
zone. Subsurface productivity is limited by nutrient availability,
as the anoxic bottom waters act as a sink for reduced nitrate, in
the form of ammonia. The benthic zone also plays an important
role in Black Sea nutrient cycling, as chemosynthetic organisms
and anoxic geochemical pathways recycle nutrients which can
be upwelled to the photic zone, enhancing productivity

8. The effect of pollution on Black Sea
ecology Pollution reduction and
• Since the 1960s, rapid
industrial expansion along the
Black Sea coast line and the
regulation efforts have led to construction of a major dam
a partial recovery of the has significantly increased
Black Sea ecosystem during annual variability in the N:P:Si
the 1990s, and an EU ratio in the basin. In coastal
areas, the biological effect of
monitoring exercise, these changes has been an
'EROS21', revealed increase in the frequency of
decreased N and P values, monospecific phytoplankton
relative to the 1989 blooms, with diatom bloom
frequency increasing by a
peak. Recently, scientists factor of 2.5 and non-diatom
have noted signs of bloom frequency increasing by
ecological recovery, in part a factor of 6. The non-diatoms,
due to the construction of such as the
prymnesiophytes Emiliania
new sewage treatment plants huxleyi (coccolithophore), Chr
in Slovakia, Hungary, omulina sp., and the
Romania, and Bulgaria in Euglenophyte Eutreptia
connection with membership lanowii are able to out-
compete diatom species
in the European because of the limited
Union. Mnemiopsis availability of Si, a necessary
leidyi populations have been constituent of diatom
checked with the arrival of frustules. As a consequence of
these blooms, benthic
another alien species which macrophyte populations were
feeds on them . deprived of light, while anoxia
caused mass mortality in
marine animals .

9. History
• The Black Sea was a busy waterway on the crossroads of the ancient
world: the Balkans to the West, the Eurasian steppes to the north,
Caucasus and Central Asia to the East, Asia Minor and Mesopotamia
to the south, and Greece to the south-west. The oldest processed
gold in the world, arguably left by Old Europeans, was found in
Varna, and the Black Sea was supposedly sailed by the Argonauts.
The land at the eastern end of the Black Sea, Colchis, (now Georgia),
marked for the Greeks an edge of the known world. The steppes to
the north of the Black Sea have been suggested as the original
homeland (Urheimat) of the speakers of the Proto-Indo-European
language, (PIE) the progenitor of the Indo-European
language family, by some scholars (see Kurgan; others move the
heartland further east towards the Caspian Sea, yet others
to Anatolia). Numerous ancient ports line Black Sea's coasts, some
older than the pyramids.
• The Black Sea was a significant naval theatre of World War I and saw
both naval and land battles during World War II.

10. THE END!