Chemical oceanography of the Arabian sea: Part III - studies on nutrient fraction and stoichiometric relationships in the northern and the eastern basins

Abstract

Phosphorus and inorganic nitrogen compounds have been divided into 'reserved' and oxidative fractions based on their relationships with apparent oxygen utilization in the northern and the north-eastern basins of the Arabian Sea. Two oxygen minima are observed in the water masses north of 20° N latitude. The reserved nitrogen compound is negative in the deeper waters and this varies from north to south. This deficit indicates a possible loss of nitrate to gaseous nitrogen through denitrification. Spatial variation of oxidative ratios indicates changes in the rates of nutrient regeneration associated mainly with regional variations in phtosynthetic productivity. A stoichiometric relationship based on the ratios of change of nutrients in water and their ratios of concentration in plankton indicates that organisms in the Arabian Sea may have an atomic relation for C:N:P of 105:15:1. Applying the oxidative ratios the losss of nitrate through denitrification has been calculated to be about 2/3 of its total availability. Similarity of conditions between this area and the eastern tropical North Pacific suggests denitrification as a characteristic on the eastern sides of oceans which are poorly ventilated in the north.