Environmental Engineering Reference
In-Depth Information
with oxygen and sulfide) in the western central gyre (Knorr2001; Stn 6) are
compared in Fig. 11. Dissolved Mn is low in the surface layer (
5 nM) and
increases rapidly below
σ
θ
= 16.0. It increases to a maximum of about 8 to
9 µM in the upper part of the sulfide zone (
∼
200 m). The concentrations at
this maximum appear controlled by MnCO
3
saturation [64]. Mn then decreases
slowly with depth to approximately 4.5 µM at 2000 m. The deep water Mn
concentrations appear controlled by MnS
2
(haurite) solubility, rather than MnS
(alabandite) or MnCO
3
(rhodochrosite) solubility [31].
∼
Figure 11.
Vertical distributions versus density of oxygen, sulfide (left) and dissolved and
particulate manganese (right) in the central gyre of the western basin of the Black Sea. From
Knorr 2001 Leg 1 Station 6 and Leg 2 Station 2. Data from B. Tebo and B. Clement, UCSD,
personal communication.
There is an upward flux of dissolved reduced Mn (as Mn (II)) that is oxi-
dized in the suboxic zone. Mn-oxidizing bacteria are active in this layer [69].
Particulate Mn has a well formed maximum centered at
∼
σ
θ
= 16.0 (Fig. 11).
There are significant spatial variations in the distributions of particulate Mn
[69]. There are sometimes two maxima where the shallower maximum corre-
sponds to the maximum specific oxidation rates of Mn but appears to consist of
adsorbed Mn (II) rather than oxidized Mn. The deeper maximum is composed
of Mn (III, IV) manganate material. Tebo [69] hypothesized that particulate
oxidized Mn is transported laterally from coastal sites where Mn cycling is
