Abstract
Based on our measurements during the German Arabian Sea Process Study as part of the Joint Global Ocean Flux Study (JGOFS) in 1995 and 1997, we present estimates of various N sources and sinks such as atmospheric deposition of N aerosols, pelagic denitrification, nitrous oxide emissions, and advective N input from the south. Additionally, we estimated the N burial in the deep sea and the sedimentary shelf denitrification. The reassessed N budget is dominated by the N loss due to denitrification which is balanced by the advective input of N through from the south. Atmospheric N depositions are important on a regional scale during the intermonsoon in the central Arabian Sea; however, they play only a minor role for the overall N cycling. Emissions of nitrous oxide and ammonia, N fixation, deep sea N burial, and N inputs by rivers and marginal seas (i.e., Persian Gulf and Red Sea) are negligible. We found that the magnitude of the sedimentary denitrification at the shelf is comparable to the pelagic denitrification. Therefore, we conclude that the shelf sediments of the Arabian Sea might be of considerably greater importance for the N cycling in the Arabian Sea than previously thought. The main northward transport of N into the Arabian Sea occurs in the intermediate layers indicating that the N cycle of the Arabian Sea might be sensitive to variations of the intermediate water circulation of the Indian Ocean.