Tropospheric and dissolved N2O of the west Pacific and east Indian Oceans during the El Niño Southern Oscillation event of 1987

Abstract

Over 2000 measurements of N 2 O in the surface water and marine troposphere along with 650 measurements of N 2 O from depths of up to 6000 m were obtained from the W. Pacific and E. Indian oceans during the late spring and early summer of 1987. The precision (1 standard deviation) for tropospheric, surface water, and deep‐water measurements was 0.2%, 1%, and 2%. The results show a latitudinally weighted, mean interhemispheric difference of 0.97 ppb, which suggests that 2/3 of the global flux of N 2 O into the atmosphere derives from sources in the northern hemisphere. The mean surface water saturation anomaly was only 2.5% during this study, which included subtropical gyres, current confluences and divergences, and some shelf waters. Supersaturations of dissolved N 2 O that might normally be associated with equatorial upwelling in the W. Pacific were depressed along with other upwelling indicators. Our surface water flux estimates suggest that the oceanic flux of N 2 O during an El Niño year may be less than 50 Gmol yr−1 (about 10% of the mean annual flux of N 2 O into the troposphere). Deep‐water N 2 O concentrations, which could be predicted with reasonable certainty from salinity, temperature, dissolved O 2, and pressure, were highest in N. Pacific waters and lowest in the higher latitudes of S. Pacific and E. Indian oceans.