Environmental Engineering Reference
In-Depth Information
The bathymetry of the Black Sea and the topography of the surrounding land
masses are shown in Fig. 1. The narrow (0.76 - 3.60 km) and shallow (
<
93
m) Bosporus Strait provides the only pathway of water exchange between the
Black Sea and the Mediterranean. The sill depths of the Bosporus are 32-34
m at the southern end and 60 m at the northern end [18, 29] The seawater
that flows into the Black Sea from the Mediterranean along the bottom of
the Bosporus Strait is the only source of salty water to the basin. Deep-water
salinity values increase to S = 22.33. Freshwater inflow from several European
rivers (especially the Danube, Dniester, Dnieper, Don and Kuban) keeps the
salinity low in the surface layer (S
18.0 to 18.5 in the central region). As a
result, the water column is strongly stratified with respect to salinity, which is
the main control of density. The main water fluxes are summarized in Table 1.
These values show that evaporation exceeds precipitation and that the surface
outflow is about twice as large as the deep inflow through the Bosporus. The
currents in both directions are very strong (ms
−
1
).
≈
Table 1.
Present-day water fluxes of the Black Sea.
350 km
3
y
−
1
River input (Total)
250 km
3
y
−
1
Danube River
Dniester
8
Dnieper
51
Don
28
Kuban
12
303 km
3
y
−
1
Precipitation
350 km
3
y
−
1
Evaporation
313 km
3
y
−
1
Bosporus outflow to Black Sea
average Bosporus deep salinity
= 34.9
= 14.5
◦
C - 15.0
◦
C in summer
= 12.5
◦
C - 13.5
◦
C in winter
average Bosporus deep temperature
Bosporus outflow to Marmara Sea
610 km
3
y
−
1
Slope of water surface along the
35 cm
Bosporus from north to south
Current Velocities (surface)
∼
2ms
−
1
(deep)
∼
0.5ms
−
1
(but reaching
∼
1.5ms
−
1
over sills)
A consequence of the vertical stratification is that the surface layer (about
0 to 50 m) is well oxygenated while the deep layer (100 m to 2000 m) is
anoxic and contains high concentrations of hydrogen sulfide. At the boundary
between the oxic surface and anoxic deep layers, there is a suboxic zone
(between approximately 50 to 100 m depth) where the concentrations of both
O
2
and H
2
S are extremely low (
<
3 µM) and do not exhibit significant vertical
or horizontal gradients in the central gyre regions on a given density surface in
