Ammonia in the oceanic atmosphere and the cycle of nitrogen compounds through the atmosphere and the hydrosphere

Abstract

The concentration of ammonia in the atmosphere over the ocean was determined for samples collected on board. The concentration of total ammonia in the maritime air was 50ng at/m3(STP) on the average which was much lower than that over the land, and was higher in the air nearer the land. The proportion of aerosol ammonia to total ammonia in the maritime air was 30% (mean) in the North Pacific, whereas it was 80% in the South Pacific. These facts together with the residence time of ammonia in the atmosphere suggest that most of ammonia in the oceanic air is of continental origin. The amount of combined nitrogen transported from the land to the ocean is estimated from its concentration in rain water to be 1.5 × 1012g at N/y. Judging from the budget of the combined nitrogen in the ocean, the large supply of nitrogen from the land is balanced by the denitrification in the ocean. Its mechanism is discussed from the quantitative aspect, and two possibilities still remain owing to the lack of decisive evidences, which are the reduction of nitrate in sea water containing little oxygen and the denitrification in the respiratory process in oxygenated sea water.