If this is admitted the poverty of tropical sea-water in mineral nitrogen compounds is explained by the higher temperature, which accelerates the activity of denitrifying bacteria.
There is also another possible source of loss of nitrates through the activity of denitrifying bacteria.
The relative abundance of nitrates and nitrites at the bottom of deep oceans as compared with the surface can be explained in the same way, for at the bottom the temperature is about zero Centigrade and the activities of the denitrifying bacteria are practically suspended.
Denitrifying bacteria will raise the alkalinity (or reduce the H-ion concentration) by forming ammonia, which will combine with the carbonic acid in solution and so throw down normal carbonate of lime.
Quietly and with no publicity, emergency denitrifying water treatment plants have been built for the time when levels rise to alarming proportions.