484
Chemical Oceanography, 4th Edition
increase from the surface down to the bottom of the intermediate layer (~20 m), which
contributed to the large pycnocline. A secondary halocline was also observed at about 90
m. The salinity in the surface waters was about 13.26, which is much higher than the value
found during the 1989 cruise. Both cruises were at the same time of the year. These results
suggest that the local freshwater supply to the Framvaren may vary annually.
The dissolved oxygen in the surface water was 283 μM, which is close to the saturated
value (285 μM). The maximum value of 292 μM in the subsurface (6 m) is the result of photosynthesis. The oxygen concentration decreased sharply from 15 m and became undetectable below 18 m (Figure 10.68). The H 2 S appeared at 20 m (0.4 μM), which corresponded
to the σ T = 15.8 isopycnal surface. The interface at 18 m showed no overlap in the levels of
O 2 and H 2 S within the sampling scale (1 m). The interface was located at 18 m (σ T = 16.52)
in 1979, at 18 m (σ T = 15.8 to 15.9) in 1985, and at 19 m (σ T = 15.60) in 1989. The oxic–anoxic
interface has been relatively stable during the past 20 years based on the depth resolution
of Niskin bottles. Small fluctuations, however, are expected to be caused by changes in the
exchange of water with outside basin and internal waves. The concentrations of H 2 S in the
bottom water were found to be as high as 5.8 mM, which is in reasonable agreement with
the results of Landing and Westerlund (6.1 mM; 1988) and Millero (5.7 mM; 1991b). The
gradient of H 2 S in the bottom water (below 100 m) was much smaller than that in the deep
water (20 to 100 m) (Millero, 1991b). This may have been due to the separation of the older
water and more recent anoxic water (Skei, 1988a,b). The distributions of nutrients TA and
TCO 2 (shown below) show the same pattern.
0
1
2
3
4
5
Fe(II) (µM)
Mn(II) (µM)
Depth (m)
O 2 , H 2 S (µM)
Fe(II)
0
4
8
12
16
20
Mn(II)
Sulfide
Oxygen
0
40
80
120
160
200
240
280
8
10
12
14
16
18
20
22
24
26
28
Figure 10.73
Concentrations of oxygen, hydrogen sulfide, Mn(II), and Fe(II) near the interface in the Framvaren Fjord.
Chemical Oceanography, 4th Edition
increase from the surface down to the bottom of the intermediate layer (~20 m), which
contributed to the large pycnocline. A secondary halocline was also observed at about 90
m. The salinity in the surface waters was about 13.26, which is much higher than the value
found during the 1989 cruise. Both cruises were at the same time of the year. These results
suggest that the local freshwater supply to the Framvaren may vary annually.
The dissolved oxygen in the surface water was 283 μM, which is close to the saturated
value (285 μM). The maximum value of 292 μM in the subsurface (6 m) is the result of photosynthesis. The oxygen concentration decreased sharply from 15 m and became undetectable below 18 m (Figure 10.68). The H 2 S appeared at 20 m (0.4 μM), which corresponded
to the σ T = 15.8 isopycnal surface. The interface at 18 m showed no overlap in the levels of
O 2 and H 2 S within the sampling scale (1 m). The interface was located at 18 m (σ T = 16.52)
in 1979, at 18 m (σ T = 15.8 to 15.9) in 1985, and at 19 m (σ T = 15.60) in 1989. The oxic–anoxic
interface has been relatively stable during the past 20 years based on the depth resolution
of Niskin bottles. Small fluctuations, however, are expected to be caused by changes in the
exchange of water with outside basin and internal waves. The concentrations of H 2 S in the
bottom water were found to be as high as 5.8 mM, which is in reasonable agreement with
the results of Landing and Westerlund (6.1 mM; 1988) and Millero (5.7 mM; 1991b). The
gradient of H 2 S in the bottom water (below 100 m) was much smaller than that in the deep
water (20 to 100 m) (Millero, 1991b). This may have been due to the separation of the older
water and more recent anoxic water (Skei, 1988a,b). The distributions of nutrients TA and
TCO 2 (shown below) show the same pattern.
0
1
2
3
4
5
Fe(II) (µM)
Mn(II) (µM)
Depth (m)
O 2 , H 2 S (µM)
Fe(II)
0
4
8
12
16
20
Mn(II)
Sulfide
Oxygen
0
40
80
120
160
200
240
280
8
10
12
14
16
18
20
22
24
26
28
Figure 10.73
Concentrations of oxygen, hydrogen sulfide, Mn(II), and Fe(II) near the interface in the Framvaren Fjord.