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Chemical Oceanography, 4th Edition
matter without fractionation, and DON removal is by fractionation. The NH 4 produced
and organic nitrogen compounds are taken up by plankton. In summary, the measurements of 15 N/ 14 N can be useful in understanding the complications that control nitrogen
in the surface oceans.
8.3.4 Nitrogen–Phosphorus ratio
The N:P ratio assimilated from seawater by phytoplankton as they grow is about 15:1.
Lower values are found in coastal waters. For example, in the English Channel, winter
values are 10.5:1, while in the summer they are 19:1. The P:N:C ratio in phytoplankton
is 1:16:106 (Redfield, 1958). From Liebig’s law of minimum (the concentration present in
N 2 O (µM)
0
5
10 15 20 25 30
Depth (m)
0
1000
2000
3000
4000
5000
6000
O 2 (µM)
150
200
250
300
Depth (m)
0
1000
2000
3000
4000
5000
6000
Figure 8.15
Profiles of nitrogen oxide and oxygen in the Atlantic Ocean.
O 2 (µM)
0
50
100
150
200
250
N
2 O (µM)
0
10
20
30
40
50
Oxic waters
Anoxic waters
Figure 8.16
The relationship between nitrogen oxide and oxygen in Pacific Ocean waters.