243
Dissolved Gases Other than CO 2
The amount of I 3
– formed is equivalent to the O 2 in the solution and is determined by titration with sodium thiosulfate:
I 3
– + 2S 2 O 3
2– → 3I – + S 4 O 6
2–
(6.47)
A starch solution that forms a blue complex with I 2 is used to determine the end point. The
concentration of O 2 can also be measured using O 2 electrodes or by gas chromatography.
The electrode system has been attached to conductivity- temperature- depth (CTD) systems
to obtain continuous profiles of O 2 in ocean waters.
The vertical distribution of O 2 in the major oceans is shown in Figure 6.9. In surface
waters, the O 2 concentrations in seawater are close to the expected values for the temperature and salinity of the waters. This is shown in Figure 6.10 for the measurements
made during the Geochemical Oceans Sections Study (GEOSECS) program. The solid line
represents the saturation value. The surface values are 7 μmol kg –1 , or about 3% supersaturated. This supersaturation can be attributed to bubble injection and photosynthesis. In
the photosynthetic zone, the O 2 will go through a maximum because of photosynthesis
(see Figure 6.11).
The most remarkable features of the O 2 profile in the major oceans are the minimum
layer and the relatively high O 2 in deep waters. The minimum is the result of a balance
between the biological oxidation of plant material and the advection of cold waters rich in
O 2 . The advection of oxygen- rich waters in the oceans is more clearly demonstrated in the
sections of O 2 in the Atlantic, Pacific, and Indian Oceans given in Figure 6.12. The intrusion
of Antarctic and Arctic intermediate waters is evident in the Atlantic, Pacific, and Indian
δ
4 He (%)
0
10
20
30
40
50
δ
3
He (%)
0
10
20
30
40
50
Air Injection
Figure 6.8
Values of helium-3 versus helium-4 for Pacific Ocean waters compared to expected values from air injection.
Dissolved Gases Other than CO 2
The amount of I 3
– formed is equivalent to the O 2 in the solution and is determined by titration with sodium thiosulfate:
I 3
– + 2S 2 O 3
2– → 3I – + S 4 O 6
2–
(6.47)
A starch solution that forms a blue complex with I 2 is used to determine the end point. The
concentration of O 2 can also be measured using O 2 electrodes or by gas chromatography.
The electrode system has been attached to conductivity- temperature- depth (CTD) systems
to obtain continuous profiles of O 2 in ocean waters.
The vertical distribution of O 2 in the major oceans is shown in Figure 6.9. In surface
waters, the O 2 concentrations in seawater are close to the expected values for the temperature and salinity of the waters. This is shown in Figure 6.10 for the measurements
made during the Geochemical Oceans Sections Study (GEOSECS) program. The solid line
represents the saturation value. The surface values are 7 μmol kg –1 , or about 3% supersaturated. This supersaturation can be attributed to bubble injection and photosynthesis. In
the photosynthetic zone, the O 2 will go through a maximum because of photosynthesis
(see Figure 6.11).
The most remarkable features of the O 2 profile in the major oceans are the minimum
layer and the relatively high O 2 in deep waters. The minimum is the result of a balance
between the biological oxidation of plant material and the advection of cold waters rich in
O 2 . The advection of oxygen- rich waters in the oceans is more clearly demonstrated in the
sections of O 2 in the Atlantic, Pacific, and Indian Oceans given in Figure 6.12. The intrusion
of Antarctic and Arctic intermediate waters is evident in the Atlantic, Pacific, and Indian
δ
4 He (%)
0
10
20
30
40
50
δ
3
He (%)
0
10
20
30
40
50
Air Injection
Figure 6.8
Values of helium-3 versus helium-4 for Pacific Ocean waters compared to expected values from air injection.