350
Chemical Oceanography, 4th Edition
levels, denitrogenation is more important than anammox. In the ETSP, anammox is an
important way N 2 is formed. The anammox is fueled by the NH 4 from dissimilatory nitrate
reduction to anammox (DNR).
As discussed, N 2 O is formed in the oxygen minimum layer. This is shown in
Figure 8.15, where the estimated concentration of NO 3
– is compared to the values calculated from the concentration of PO 4
3– and assuming N/ P = 16. This deficiency in
NO 3
– is due to the amount used by bacteria to oxidize organic carbon in water with
low oxygen. The nitrate is reduced to N 2 O as is shown in Figure 8.15. The excess N 2 O
Atlantic
Pacific
Indian
35
30
25
20
15
10
5
0
35
30
25
20
15
10
5
0
0
10
20
30
40
EQ
Ocean Data View
Ocean Data View
Ocean Data View
20°S
60°S
40°S
EQ
20°N
40°N
40°S
20°S
EQ
20°N
40°N
60°N
40°S
20°S
Depth (m)
5000
4000
3000
2000
1000
0
Depth (m)
5000
4000
6000
3000
2000
1000
0
Depth (m)
4000
3000
2000
1000
0
Indian Ocean I8
P16
I8
A16
Pacific Ocean P16
Nitrate (µmol/kg)
Nitrate (µmol/kg)
Nitrate (µmol/kg)
Figure 8.10
Sections of nitrate in the Atlantic, Pacific, and Indian Oceans.