CHAPTER 4 . Redox Processes in Anoxic Waters
107
Fig. 4.15. Profiles of ammonia,
[Si0 2 ) (jJM)
phosphate, and silicate in
0
200
400
600
800
the Framvaren Fjord (Yao and
Millero 1995b)
(POJ(jJM)
o 0
30
60
90
120
150
20
40
60
g
80
oJ:
100
Q.
~ 120
140
~P04
160
- . . . Si0 2
--T- NH4
180
200
0
400
800
1200
1600
INHJ (jJM)
At present, it is difficult to balance the sulfur budget in the Framvaren due to the
incomplete measurements of all the sulfur species (especially the particulate sulfur,
SO and FeSz) and organic sulfur compounds. The ratio of thiols (mercaptants) RSH to
HzS was found to be 0.036 in the Framvaren (Dyrssen 1988). The difference between
the initial sulfate concentration, [S04Lnt> as calculated from salinity, and the measured
sulfate concentration is found to be significantly higher (1-3 mM) than the measured
sulfide in bottom water. This discrepancy is explained by the removal of sulfide by
oxidation and the formation of iron sulfides (FeS and FeS2)' in addition to the possible diffusion ofH2S. If the major product of oxidation ofH2S is sulfate (Millero 1991b),
the discrepancy may be even higher. The removal of sulfide by the formation of iron
sulfides is restricted to a continuing supply of iron. At pH = 7.0, about 30% of the total
hydrogen sulfide is in H2S(aq). Diffusion might be a pathway for HzS to escape into upper oxic water and be oxidized. In addition, there is evidence for the early diagenetic
incorporation of inorganic sulfur into organic compounds.
The normalized TA (NTA = TA x 35 / 5) and normalized TC02 (NTC02 = TCOz x 35 / 5)
in the bottom waters of the Framvaren are about 12 times more than in the open ocean,
suggesting an enormous production of both TA and TC0 2 from oxidation of organic
matter through the reduction of sulfate. The value of NTA in the Framvaren surface
water was 2.41 mM, which is only slightly higher than the typical value of the open
ocean (2.35 mM), while the NTC02 is much higher (2.31 mM) than the value of the
open ocean (2.05 mM). The lower NTA in the Framvaren surface water indicates that
107
Fig. 4.15. Profiles of ammonia,
[Si0 2 ) (jJM)
phosphate, and silicate in
0
200
400
600
800
the Framvaren Fjord (Yao and
Millero 1995b)
(POJ(jJM)
o 0
30
60
90
120
150
20
40
60
g
80
oJ:
100
Q.
~ 120
140
~P04
160
- . . . Si0 2
--T- NH4
180
200
0
400
800
1200
1600
INHJ (jJM)
At present, it is difficult to balance the sulfur budget in the Framvaren due to the
incomplete measurements of all the sulfur species (especially the particulate sulfur,
SO and FeSz) and organic sulfur compounds. The ratio of thiols (mercaptants) RSH to
HzS was found to be 0.036 in the Framvaren (Dyrssen 1988). The difference between
the initial sulfate concentration, [S04Lnt> as calculated from salinity, and the measured
sulfate concentration is found to be significantly higher (1-3 mM) than the measured
sulfide in bottom water. This discrepancy is explained by the removal of sulfide by
oxidation and the formation of iron sulfides (FeS and FeS2)' in addition to the possible diffusion ofH2S. If the major product of oxidation ofH2S is sulfate (Millero 1991b),
the discrepancy may be even higher. The removal of sulfide by the formation of iron
sulfides is restricted to a continuing supply of iron. At pH = 7.0, about 30% of the total
hydrogen sulfide is in H2S(aq). Diffusion might be a pathway for HzS to escape into upper oxic water and be oxidized. In addition, there is evidence for the early diagenetic
incorporation of inorganic sulfur into organic compounds.
The normalized TA (NTA = TA x 35 / 5) and normalized TC02 (NTC02 = TCOz x 35 / 5)
in the bottom waters of the Framvaren are about 12 times more than in the open ocean,
suggesting an enormous production of both TA and TC0 2 from oxidation of organic
matter through the reduction of sulfate. The value of NTA in the Framvaren surface
water was 2.41 mM, which is only slightly higher than the typical value of the open
ocean (2.35 mM), while the NTC02 is much higher (2.31 mM) than the value of the
open ocean (2.05 mM). The lower NTA in the Framvaren surface water indicates that