Variabilities in the fluxes and annual emissions of nitrous oxide from the Arabian Sea

Abstract

Extensive measurements of nitrous oxide (N₂O) have been made during April-May 1994 (intermonsoon), February-March 1995 (northeast monsoon), July-August 1995 and August 1996 (southwest monsoon) in the Arabian Sea. Low N₂O supersaturations in the surface waters are observed during intermonsoon compared to those in northeast and southwest monsoons. Spatial distributions of supersaturations manifest the effects of larger mixing during winter cooling and wind-driven upwelling during monsoon period off the Indian west coast. A net positive flux is observable during all the seasons, with no discernible differences from the open ocean to coastal regions. The average ocean-to-atmosphere fluxes of N₂O are estimated, using wind speed dependent gas transfer velocity, to be of the order of 0.26, 0.003, and 0.51, and 0.78 pg (pico grams) cm^-2 s^-1 during northeast monsoon, intermonsoon, and southwest monsoon in 1995 and 1996, respectively. The lower range of annual emission of N₂O is estimated to be 0.56-0.76 Tg N₂O per year which constitutes 13-17% of the net global oceanic source. However, N₂O emission from the Arabian Sea can be as high as 1.0 Tg N₂O per year using different gas transfer models.