488
Chemical Oceanography, 4th Edition
the bottom layer and be smoothed out by diffusion. The uniform properties in the bottom
layer suggested that it was produced and maintained by convection, probably driven by
geothermal heat from the sediments. The temperature and salinity both increased slightly
below 80 m, so the vertical transport is possibly controlled by double diffusion. Double
diffusion takes place when the gradients of temperature and salinity have the same sign
and thus have opposite effects on density.
The temperature of the bottom water showed a significant decrease of 1.1°C from the
1930s to the present (Figure 10.80). This suggests that the heat flow to the bottom water,
probably geothermal heating from sediments, was decreasing. The salinity in the bottom
water also showed a decreasing trend. This decrease in salinity implies that the renewal of
the bottom water was with the lighter water above by vertical diffusion. Vertical diffusion
might also account for the decrease of temperature in the bottom water.
At present, it is not possible to establish a complete balance of sulfur in the Framvaren
because of the incomplete measurements of sulfur species, especially the particulate sulfur (such as S 0 and FeS 2 ) and organic sulfur compounds. The ratio of thiols (mercaptans)
to H 2 S was found to be 0.036 in the Framvaren (Dyrssen, 1989). The difference between
the initial sulfate concentration, ([SO 4 ] init ), as calculated from salinity, and the measured
sulfate concentration was significantly higher (1 to 3 mM) than the measured sulfide in
bottom water. This discrepancy is explained by the removal of sulfide by oxidation and
formation of iron sulfides (FeS and FeS 2 ), in addition to the possible diffusion of H 2 S. If the
major product of the oxidation of H 2 S is sulfate (Millero, 1991a), the discrepancy may have
0
4
8
12
16
20
24
0
20
40
60
80
100
120
140
160
180
200
TA
TCO 2
pH
TCO 2 (mM)
6.6
6.8
7.0
7.2
7.4
7.6
7.8
8.0
pH
0
4
8
12
16
20
Depth (m)
TA (mM)
Figure 10.77
Profiles of pH, TCO 2 , and TA in the Framvaren Fjord.
Chemical Oceanography, 4th Edition
the bottom layer and be smoothed out by diffusion. The uniform properties in the bottom
layer suggested that it was produced and maintained by convection, probably driven by
geothermal heat from the sediments. The temperature and salinity both increased slightly
below 80 m, so the vertical transport is possibly controlled by double diffusion. Double
diffusion takes place when the gradients of temperature and salinity have the same sign
and thus have opposite effects on density.
The temperature of the bottom water showed a significant decrease of 1.1°C from the
1930s to the present (Figure 10.80). This suggests that the heat flow to the bottom water,
probably geothermal heating from sediments, was decreasing. The salinity in the bottom
water also showed a decreasing trend. This decrease in salinity implies that the renewal of
the bottom water was with the lighter water above by vertical diffusion. Vertical diffusion
might also account for the decrease of temperature in the bottom water.
At present, it is not possible to establish a complete balance of sulfur in the Framvaren
because of the incomplete measurements of sulfur species, especially the particulate sulfur (such as S 0 and FeS 2 ) and organic sulfur compounds. The ratio of thiols (mercaptans)
to H 2 S was found to be 0.036 in the Framvaren (Dyrssen, 1989). The difference between
the initial sulfate concentration, ([SO 4 ] init ), as calculated from salinity, and the measured
sulfate concentration was significantly higher (1 to 3 mM) than the measured sulfide in
bottom water. This discrepancy is explained by the removal of sulfide by oxidation and
formation of iron sulfides (FeS and FeS 2 ), in addition to the possible diffusion of H 2 S. If the
major product of the oxidation of H 2 S is sulfate (Millero, 1991a), the discrepancy may have
0
4
8
12
16
20
24
0
20
40
60
80
100
120
140
160
180
200
TA
TCO 2
pH
TCO 2 (mM)
6.6
6.8
7.0
7.2
7.4
7.6
7.8
8.0
pH
0
4
8
12
16
20
Depth (m)
TA (mM)
Figure 10.77
Profiles of pH, TCO 2 , and TA in the Framvaren Fjord.