461
Processes in the Oceans
to the oxidation of organic carbon with O 2 . At the interface, the phosphate levels decrease
dramatically and increase below the interface in the anoxic waters. This is due to the
adsorption of PO 4
3– to MnO 2 (s) and Fe(OH) 3 (s) in the oxic waters and release in the anoxic
waters caused by the reactions of the oxides with H 2 S and formation of reduced Fe(II) and
Mn(II). These adsorption and dissolution processes occur at the interface of most anoxic
basins. The nitrate levels increase in the oxic waters because of the oxidation of NH 3 with
Table 10.8
Anoxic Basins
Name
Location
Bottom (m)
Sill (m) Maximum H 2 S (μM)
Goteland Deep
Baltic Sea
249
60
20
Cariaco Trench
Caribbean Sea
1390
150
160
Lake Nitinat
British Columbia
250
4
250
Saanich Inlet
British Columbia
236
65
250
Black Sea
Europe
2243
40
350
Framvaren
Norway
350
2
6000
6000
5000
Mn (nmol L –1 )
Fe (nmol L –1 )
Labile Co (pmol L
–1 )
Total Co (pmol L
–1 )
4000
3000
Distance (km)
2000
1000
Depth (m)
Depth (m)
Depth (m)
Depth (m)
0
0
0.25
0.5
0.75
1.25
1.75
0
1.5
0.5
1.5
0
10
15
20
25
30
35
0
30
60
90
120
27
23
19*
17
13
7
4
1
0
2000
4000
2000
4000
2000
4000
4000
2000
0
0
0
5
1
1
Figure 10.43
Basin-scale inputs of Co, Fe, and Mn from hydrothermal vents.