Seasonal and spatial variability in N₂O distribution in the Arabian Sea

Abstract

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.