Environmental Engineering Reference
In-Depth Information
σ
θ
= 16.2 to 16.6 from the central western
gyre to the southwest region near the Bosporus Plume [from 26].
Figure 13.
Horizontal gradients of sulfide from
low and it moved to deeper density layers. Ventilation of the CIL from the
surface was enhanced and oxygen concentrations on
σ
θ
= 15.4 were higher.
This density surface was chosen because it is just above the upper boundary of
the suboxic zone. The years 1987 and 2001 had lower oxygen concentrations
on
σ
θ
= 15.4 and followed warm periods with less CIL formation and resulted
in higher temperatures. As a result the suboxic layer became thicker. The
increased ventilation resulting from the cold winters of 2002 and 2003 resulted
in a thinner suboxic zone.
The temporal variation of O
2
and temperature on
σ
θ
= 15.4 is shown in Fig.
15. In the 1960s and early 1970s the temperature - oxygen data varied along
an inverse trend (lower temperature had higher oxygen). The dashed lines are
visual fits to the data. Starting in the late 1970s there was a shift to a new trend
with a similar slope but at lower oxygen values. The nutrient concentrations and
inventories (especially nitrate) in the euphotic zone of the Black Sea increased
during this period [25]. We interpret this shift as resulting from increased
eutrophication in the Black Sea due to increased nutrient fluxes from rivers.
The eutrophication probably resulted in an increased flux of organic matter that
resulted in increased oxygen consumption.
