CHAPTER 4 . Redox Processes in Anoxic Waters
103
Fig. 4.12. Profiles of oxygen
[021( ~M)
and hydrogen sulfide in the
0
50
100
150
200
250
300
350
Framvaren Fjord (Yao and
0
Millero 1995b)
20
Oxygen
40
60
g 80
.s;
is.
~ 100
120
140
160
180
0
2
4
6
8
[H2S1(~M)
sharply from 15 m and became undetectable below 18 m. The oxic/anoxic interface has
been relatively stable during the last 20 years. Small fluctuations, however, are expected
to occur due to changes in the exchange of water with outside basin and internal waves.
The concentrations of H2S in the bottom water were found to be as high as 5.8 mM.
The gradient of H2S in the bottom water (below 100 m) is much smaller than that in
the deep water (20-100 m) (Millero 1991b). This may be due to the separation of the
older water and more recent anoxic water. The distributions of nutrients, TA and Te0 2
(shown below) show the same pattern.
The concentration of metals in the Framvaren determined by Haraldsson and
Westerlund (1988) are shown in Fig. 4.13a,b. The profiles are similar to those found in
other anoxic basins. The metals Mn2+, Fe 2 +, C0 2 + have the characteristic maximum near
the oxic/anoxic interface; Ni 2 + shows no changes across the interface; and the metals
Cu 2 +, Zn 2 + and Cd2+ show large decreases in the concentration at the interface due to
the low solubility of their metal sulfides. The oxidation ofH 2 S with O 2 in the Framvaren
has been shown to be greatly enhanced by the high content of Fe and Mn (Yao and
Millero 1995b). Only low levels of the intermediates SO~- and S20~- were found near
the interface.
The dissolved Mn and Fe together with O2 and H2S near the interface are shown in
Fig. 4.14 (Yao and Millero 1995b). The concentration of dissolved Mn increases rapidly
below 15 m, corresponding to the rapid decrease of O2 and reaches a maximum at 21 m
where the concentration of H2S was 12 flM. The maximum dissolved Mn found in this
study, 18.0 flM, is higher than previous values of 10.5 flM (Jacobs et al.1985) and 15.3 flM
103
Fig. 4.12. Profiles of oxygen
[021( ~M)
and hydrogen sulfide in the
0
50
100
150
200
250
300
350
Framvaren Fjord (Yao and
0
Millero 1995b)
20
Oxygen
40
60
g 80
.s;
is.
~ 100
120
140
160
180
0
2
4
6
8
[H2S1(~M)
sharply from 15 m and became undetectable below 18 m. The oxic/anoxic interface has
been relatively stable during the last 20 years. Small fluctuations, however, are expected
to occur due to changes in the exchange of water with outside basin and internal waves.
The concentrations of H2S in the bottom water were found to be as high as 5.8 mM.
The gradient of H2S in the bottom water (below 100 m) is much smaller than that in
the deep water (20-100 m) (Millero 1991b). This may be due to the separation of the
older water and more recent anoxic water. The distributions of nutrients, TA and Te0 2
(shown below) show the same pattern.
The concentration of metals in the Framvaren determined by Haraldsson and
Westerlund (1988) are shown in Fig. 4.13a,b. The profiles are similar to those found in
other anoxic basins. The metals Mn2+, Fe 2 +, C0 2 + have the characteristic maximum near
the oxic/anoxic interface; Ni 2 + shows no changes across the interface; and the metals
Cu 2 +, Zn 2 + and Cd2+ show large decreases in the concentration at the interface due to
the low solubility of their metal sulfides. The oxidation ofH 2 S with O 2 in the Framvaren
has been shown to be greatly enhanced by the high content of Fe and Mn (Yao and
Millero 1995b). Only low levels of the intermediates SO~- and S20~- were found near
the interface.
The dissolved Mn and Fe together with O2 and H2S near the interface are shown in
Fig. 4.14 (Yao and Millero 1995b). The concentration of dissolved Mn increases rapidly
below 15 m, corresponding to the rapid decrease of O2 and reaches a maximum at 21 m
where the concentration of H2S was 12 flM. The maximum dissolved Mn found in this
study, 18.0 flM, is higher than previous values of 10.5 flM (Jacobs et al.1985) and 15.3 flM