Denitrification in the Arabian Sea

Abstract

Estimates of the amount of denitrification in the Arabian Sea are inconsistent, and so two methods of calculation of 'original' nitrate concentrations used in earlier studies have been reviewed. Nitrite at intermediate depths was not restricted to the Persian Gulf water; concentrations were maximal much shallower than the depths of the Persian Gulf water. The nitrate-salinity relationship used to calculate 'original' nitrate concentrations in a recent study would lead to an underestimate of nitrate deficits because the approach requires denitrification to be restricted to Persian Gulf water. A method involving oxidative ratios has been modified and used to calculate nitrate deficits. The deficits so calculated lie between the values reported earlier. The degree of denitrification decreases steadily southward. The results indicate that denitrification extends up to 11 or 12°N latitude. Taking 30 years as the average residence time of water for the layer in which denitrification occurs, the denitrification rate in the Arabian Sea has been calculated as about 3.2 × 10¹² gy^-1. This represents about 5% of the annual global denitrification.