Nitrite Metabolism in the Euphotic Layer of the Central North Pacific Ocean1

Capacities for oxidation and reduction of inorganic nitrogen in the euphotic zone of the central North Pacific were estimated from the measurement of change with time of nitrite content in seawater samples. Regardless of whether ammonia, nitrate, or nitrite was the major component, if its concentration did not exceed 5–10 µ g‐atom N/liter, then the nitrite level changed unidirectionally for 10–24 hr and followed the kinetics of a first order reaction. In surface layers shallower than 30 m, capacities for both nitrite production from nitrate and consumption of nitrite were appreciable and they were enhanced several times by illumination. Phytoplankton seems mainly responsible for these processes. Insitu capacity for nitrite consumption was higher than that for nitrite production. But ammonia oxidation prevailed in the nitrite maximum layers located at about 70‐m depth; the production rate of nitrite was of the order of 10 ‒4 µ g‐atom N liter ‒1 hr ‒1 .