Nitrite distribution and nitrate reduction in deep sea waters

Abstract

Nitrite concentrations below 200 m range from 0·013 to 0·045 μg at. N/l. in Sagami and Suruga bays. In the central Pacific along 155°W, nitrite concentrations in deep waters are less than 0·024 μg at. N/l. except in oxygen-deficient layers where more than 0·03 μg at. N/l. may occur. When incubated for several days near in situ temperatures, nitrite concentrations in samples from depth increased at a maximum rate of about 0·015 μg at. N/l./day. The increase was largely suppressed by the addition of ammonia (20 μg at. N/l. or more). Nitrite is evidently produced in the deep waters by nitrate-reducing bacteria. Incorporation of 15N, from 15N-nitrate, into nitrite and ammonia took place in samples from Sagami Bay, but denitrification (N 2-production from nitrate) was not so common. In only 3 of 8 samples from oxygen-deficient waters from two stations in the central North Pacific, was 15N 2 produced in the presence of 15N-nitrate.