Abstract
Abstract Results from a recent cruise in the Arabian Sea show a clear association of the secondary nitrite maximum with the intermediate salinity maximum originating in the Persian Gulf and Gulf of Oman. During its spreading through the Arabian Sea the Persian Gulf core layer mixes with water of higher nitrate content and low oxygen content. Reduction of nitrate to nitrite and beyond occurs at dissolved oxygen concentrations below about 7 μM1−1 and is restricted to a well defined area of the northern Arabian Sea. The original nitrate concentrations can be calculated from the salinity-nitrate relationship in waters outside this area. This, in turn, allows determination of a combined nitrogen deficit, i.e. the amount of nitrate reduced beyond nitrite. Based on limits of the spreading rate of the Persian Gulf core layer through the ArabiaSea a range for the dentrification rate of 1011 to 1012 gN yr−1 was determined. This is equivalent to about 1%, to a maximum of 10% of the global rate required for maintenance of a steady state in the distribution of nitrogen at the surface of the Earth.
Published Version
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