Particulate and dissolved organic nitrogen in the central and eastern equatorial Pacific

A wet persulfate oxidation was used to measure particulate and dissolved organic nitrogen (DON) along four transects in the central and eastern equatorial Pacific. Particulate organic nitrogen (PON) collected on glass fiber filters ranged from 0.4 to 1.6 μM in the upper 40 m and accounted for about 10% of total organic nitrogen (TON). PON collected on 0.2 μm membrane filters was 60% higher than PON collected on glass fiber filters. Most of the organic nitrogen was present as DON. DON was lowest at the equator and increased to maximum values in the upper 40 m within 2–5° north and south of the equator. The spatial distribution of TON suggests that it is biologically produced. Meridional export of TON away from the equator could account for 37–75% of nitrate assimilation. The production of DON in the upwelling system of the equatorial Pacific appears to be a major part of the nitrogen cycle.