Abstract
Depth profiles of dissolved nitrous oxide (N (sub 2) O) were measured in the central and western Arabian Sea during four cruises in May and July-August 1995 and May-July 1997 as part of the German contribution to the Arabian Sea Process Study of the Joint Global Ocean Flux Study. The vertical distribution of N (sub 2) O in the water column on a transect along 65 degrees E showed a characteristic double-peak structure, indicating production of N (sub 2) O associated with steep oxygen gradients at the top and bottom of the oxygen minimum zone. We propose a general scheme consisting of four ocean compartments to explain the N (sub 2) O cycling as a result of nitrification and denitrification processes in the water column of the Arabian Sea. We observed a seasonal N (sub 2) O accumulation at 600-800 m near the shelf break in the western Arabian Sea. We propose that, in the western Arabian Sea, N (sub 2) O might also be formed during bacterial oxidation of organic matter by the reduction of IO (sub 3) (super -) to I (super -) , indicating that the biogeochemical cycling of N (sub 2) O in the Arabian Sea during the SW monsoon might be more complex than previously thought. A compilation of sources and sinks of N (sub 2) O in the Arabian Sea suggested that the N (sub 2) O budget is reasonably balanced.