Seasonal and spatial variability in N2O distribution in the Arabian Sea

Extensive measurements of nitrous oxide (N2O) were made in the central and eastern Arabian Sea during the northeast monsoon (February–March), intermonsoon (April–May) and southwest monsoon (July–August) seasons. The latitudinal and longitudinal variations, along with seasonal changes with respect to winter convection and coastal upwelling, are clearly discernible. Vertical profiles collected down to 1000 m show that the Arabian Sea water column is supersaturated with N2O at all depths. However, N2O consumption at intermediate depths, coincident with the oxygen minimum and associated with sediment–water interfaces, and in the denitrifying zone, coincident with NO-2 secondary maxima, are also apparent. The N2O concentration varies from ∼10 nM near the surface to about 80 nM in the secondary peak region (≈800 m). Interrelationships with chemical parameters suggest nitrification to be the main process for the production of N2O in the oceanic water. Plots of apparent oxygen utilization vs production of N2O indicate a consistent linear relationship for AOU between 0 and 200 μM.