Environmental Engineering Reference
In-Depth Information
Table 2.
Characteristic density values of biogeochemical features biogeochemistry of the Black
Sea as observed during the Knorr 1988 Research Cruise. Based on data from both the eastern
and western basins. Stations in the SW region influenced by the Bosporus Plume were omitted.
The uncertainty of each value is about 0.05 density units.
Feature
Density (σ
θ
)
PO
4
shallow maximum
15.50
O
2
<
10 µM
15.70
NO
3
maximum
15.40
Mn
d
<
200 nM
15.85
Mn
p
maximum
15.85
PO
4
minimum
15.85
NO
2
maximum
15.85
NO
3
<
0.2 µM
15.95
NH
4
>
0.2 µM
15.95
Fe
d
<
10 nM
16.00
H
2
S
>
1 µM
16.15
PO
4
deep maximum
16.20
the upper 40 m (down to a density of about
σ
θ
≈
14.5) due to gas exchange
and biological production. It then decreases linearly with depth in the main
pycnocline (halocline) to
10 µM at the density level of 15.50-15.60 kg/m
3
(about 60 m). Below this depth there is usually no detectable vertical gradient
of oxygen.
The first appearance of sulfide occurs at about 90 m or
σ
θ
= 16.15 (Fig. 2)
and then sulfide increases continuously with depth to maximum values up to
400 µM by 2200 m [33]. One of the intriguing questions about the Black Sea
is what is the sink for the upward flux of sulfide [5]? Sulfide decreases to zero
before the first appearance of oxygen thus sulfide is apparently not oxidized by
the downward flux of oxygen. Several hypotheses have been made to explain
the removal of sulfide. Millero [34], Luther et al. [33] and Debolskaya and
Yakushev [11] suggested that Mn cycling plays an important role and that the
upward flux of sulfide is oxidized by a downward flux of oxidized species of
Mn (III, IV). Konovalov and Murray [25] estimated that a significant amount of
upward flux of sulfide is oxidized by O
2
injected horizontally by the Bosporus
Plume. The Bosporus Plume results in a complicated interleaving of water that
can be best seen in the high resolution
in situ
profiling data. Oxygen containing
intrusions from the Bosporus plume (deeper than
σ
θ
= 15.0) are easily seen
in the
in situ
voltammetric O
2
and H
2
S profiles from the stations of the 2001
and 2003 KNORR cruises in the southwestern part of the sea, close to the
Bosporus [26] (Fig. 6). Whenever there is a temperature maximum (a tracer
for the Bosporus Plume) there is an oxygen maximum and sulfide minimum
≤