The North Atlantic Ocean as a source of atmospheric N<sub>2</sub>O

Abstract

In 1969, 1970, and 1971 N₂O measurements of sea water were carried out during 3 cruises in the open North Atlantic ocean. Water samples were taken from the sea’s surface and from depths down to 3000 m at several stations. Surface water concentrations in the tropical-subtropical latitudes averaged 0.5 <em>μg</em> N₂O per liter sea water. For the range from 38.5° N to 48.5° N, an average of 0.4 <em>μg</em> N₂O per liter sea water was found. In the area of the Iceland–Faroe ridge, the surface water concentrations averaged 0.4 <em>μg</em> N₂O per liter' sea water when water temperatures were 10°C, and 0.5 <em>μg</em> N₂O per liter sea water when water temperatures were 5°C. The vertical N₂O concentration profiles often show two maxima: a smaller one between 100 and 200 m and a large one between 400 and 1000 m with N₂O concentrations up to 0.8 μg per liter sea water. With the exception of a few samples, the measurements indicated that the North Atlantic sea water is supersaturated with N₂O. Supersaturation values up to more than 100% were found in the upper layers of the sea water from the tropical-subtropical latitudes up to 48.5° N. Further north the N₂O supersaturation of the sea water decreases. For the upper sea water layers down to 1000 m the following average values were obtained from vertical profiles: in tropical latitudes about 66% super-saturation, in subtropical latitudes about 47%, in the range from 38.5° N to 48.5° N about 42%, and in the area of the Iceland”Faroe ridge about 12–20% supersaturation. One may conclude that the North Atlantic ocean acts as a net source of atmospheric N₂O. It is probable that the other oceans have the same ability.