495
Processes in the Oceans
particulate C:N ratios in the surface waters were found to be about 10 in June 1993 (McKee
and Skei, 1999).
A plot of concentrations of TCO 2 versus PO 4
3– in the anoxic waters (20 to 175 m) of
the Framvaren shows a C:P slope of 155 (±2) (Figure 10.83), which is much higher than the
Redfield ratio of 106 and is also higher than the value of 127 for ocean waters suggested
by Peng and Broecker (1987). These results indicate that the nutrients (N, P) show Redfield
behavior in the Framvaren, while ratios of C:N and C:P are higher. Dyrssen (1989) suggested that the excess of carbohydrates could easily be explained by the addition of tree
leaves and other terrestrial matter. It has also been proposed that phytoplankton can incorporate C, N, and P in ratios different from 106:16:1, depending on the availability of these
elements. The high C:N and C:P ratios might result from the excess supply of inorganic
carbon compared to N and P.
If we assume the C:N:P ratio of the organic matter in the Framvaren to be 155:16:1 based
on the average value for all the data (20 to 175 m), Equation 10.65 can be rewritten as
(CH 2 O) 155 (NH 3 ) 16 (H 3 PO 4 ) + 77.5SO 4
2– = 155HCO 3
– + 77.5H 2 S + 16NH 3 + H 3 PO 4 (10.73)
The increase of C:N and C:P ratios does not change the value of 2.0 for ΔTCO 2 /ΔH 2 S, while
the ratio of ΔTA/ ΔH 2 S decreases slightly from 2.3 to 2.2. The ratios of NH 4
+ and PO 4
3– to H 2 S
both decrease, from 0.30 to 0.20 and 0.019 to 0.013, respectively. We further assume that total
inorganic carbon, ammonia, and phosphate in the anoxic waters of the Framvaren are produced only through the decomposition of organic matter based on Equation 10.72, and there
are no significant removals for them. This assumption is supported, but not proved, by the fact
that the correlations between C, N, and P are better than the correlations between C, N, P, and
H 2 S. To rebalance the measured NH 4
+ :H 2 S and PO 4
3– :H 2 S ratios (0.30 and 0.019, respectively)
to the new model values (0.20 and 0.013, respectively), the initially formed H 2 S should equal
[H 2 S] initi. = (77.5/53) × [H 2 S] meas.
In other words, about 30% of the H 2 S produced from sulfate reduction has been removed,
which corresponds to 2.8 mM SO 4
2– anomalies in the bottom water. This is equal to
the estimate (about 3 mM in the bottom water) made by Dyrssen (1986) and Anderson,
Dyrssen, and Hall (1988) by calculating the SO 4
2– balance (see Figure 10.84). As discussed,
the removal of sulfide includes the processes such as oxidation, formation of FeS 2 , diffusion, and incorporation into organic matter.
If we take the initially formed H 2 S ([H 2 S] initi. ) instead of the measured values, the ratios of
TCO 2 :[H 2 S] initi. and TA:[H 2 S] initi. are 2.04 and 2.33, respectively, which are close to the model
values. The C:N ratio was 10 in the Black Sea, which is the same value as in the Framvaren.
The extremely high value of C:P may be due to the anomalous behavior of phosphate, as
discussed previously. Higher C:N and C:P ratios in the Black Sea may also have resulted
from the large influence of terrestrial inputs. The C:N:P ratio in the Cariaco Trench, which
is a typical open ocean with little terrestrial input, was 107:15:1 and agrees well with the
Redfield value.
10.3.4 The Kinetics Oxidation of Hydrogen Sulfide in Natural Waters
The production of H 2 S that occurs in stagnant basins (seas, lakes, rivers, and fjords) also
occurs in the pore water of sediments because of biological processes and in hydrothermal
systems because of geochemical processes. Molecular oxygen is the most important and
Processes in the Oceans
particulate C:N ratios in the surface waters were found to be about 10 in June 1993 (McKee
and Skei, 1999).
A plot of concentrations of TCO 2 versus PO 4
3– in the anoxic waters (20 to 175 m) of
the Framvaren shows a C:P slope of 155 (±2) (Figure 10.83), which is much higher than the
Redfield ratio of 106 and is also higher than the value of 127 for ocean waters suggested
by Peng and Broecker (1987). These results indicate that the nutrients (N, P) show Redfield
behavior in the Framvaren, while ratios of C:N and C:P are higher. Dyrssen (1989) suggested that the excess of carbohydrates could easily be explained by the addition of tree
leaves and other terrestrial matter. It has also been proposed that phytoplankton can incorporate C, N, and P in ratios different from 106:16:1, depending on the availability of these
elements. The high C:N and C:P ratios might result from the excess supply of inorganic
carbon compared to N and P.
If we assume the C:N:P ratio of the organic matter in the Framvaren to be 155:16:1 based
on the average value for all the data (20 to 175 m), Equation 10.65 can be rewritten as
(CH 2 O) 155 (NH 3 ) 16 (H 3 PO 4 ) + 77.5SO 4
2– = 155HCO 3
– + 77.5H 2 S + 16NH 3 + H 3 PO 4 (10.73)
The increase of C:N and C:P ratios does not change the value of 2.0 for ΔTCO 2 /ΔH 2 S, while
the ratio of ΔTA/ ΔH 2 S decreases slightly from 2.3 to 2.2. The ratios of NH 4
+ and PO 4
3– to H 2 S
both decrease, from 0.30 to 0.20 and 0.019 to 0.013, respectively. We further assume that total
inorganic carbon, ammonia, and phosphate in the anoxic waters of the Framvaren are produced only through the decomposition of organic matter based on Equation 10.72, and there
are no significant removals for them. This assumption is supported, but not proved, by the fact
that the correlations between C, N, and P are better than the correlations between C, N, P, and
H 2 S. To rebalance the measured NH 4
+ :H 2 S and PO 4
3– :H 2 S ratios (0.30 and 0.019, respectively)
to the new model values (0.20 and 0.013, respectively), the initially formed H 2 S should equal
[H 2 S] initi. = (77.5/53) × [H 2 S] meas.
In other words, about 30% of the H 2 S produced from sulfate reduction has been removed,
which corresponds to 2.8 mM SO 4
2– anomalies in the bottom water. This is equal to
the estimate (about 3 mM in the bottom water) made by Dyrssen (1986) and Anderson,
Dyrssen, and Hall (1988) by calculating the SO 4
2– balance (see Figure 10.84). As discussed,
the removal of sulfide includes the processes such as oxidation, formation of FeS 2 , diffusion, and incorporation into organic matter.
If we take the initially formed H 2 S ([H 2 S] initi. ) instead of the measured values, the ratios of
TCO 2 :[H 2 S] initi. and TA:[H 2 S] initi. are 2.04 and 2.33, respectively, which are close to the model
values. The C:N ratio was 10 in the Black Sea, which is the same value as in the Framvaren.
The extremely high value of C:P may be due to the anomalous behavior of phosphate, as
discussed previously. Higher C:N and C:P ratios in the Black Sea may also have resulted
from the large influence of terrestrial inputs. The C:N:P ratio in the Cariaco Trench, which
is a typical open ocean with little terrestrial input, was 107:15:1 and agrees well with the
Redfield value.
10.3.4 The Kinetics Oxidation of Hydrogen Sulfide in Natural Waters
The production of H 2 S that occurs in stagnant basins (seas, lakes, rivers, and fjords) also
occurs in the pore water of sediments because of biological processes and in hydrothermal
systems because of geochemical processes. Molecular oxygen is the most important and