Nutrient uptake and regeneration ratios in the Red sea with reference to the nutrient budgets

Abstract

The relationships between apparent oxygen utilization and inorganic micronutrients have been studied on the basis of extensive observation in the Red Sea. The ratios obtained are - Delta AOU: Delta SiO4: Delta NO3: Delta PO4 = 23:17:21:1. The departures of the observed ratios from the corresponding open-ocean values are presumably caused by the prevailing low levels of nutrients and a relative deficiency in phosphate as compared to nitrate in the Red Sea. The composition of organic matter within the Red Se, however, appears to be rather uniform and the atomic ratios between carbon, nitrogen and phosphorus in the biomass are deduced to be 188:21:1. Increased input of nutrients associated with subsurface inflow of nutrient-rich waters from the Gulf of Aden to the Red Sea does not seem by itself to make up the apparent deficits in all nutrients, as suggested by earlier workers. Due to the high Delta NO3: Delta PO ratio observed in the Red Sea, more nitrate relative to phosphate appears to escape the Red Sea with the outflowing high-salinity water than the quantity added by the inflowing current, Assuming that the conservation of phosphate is maintained by increased inputs from the Gulf of Aden in late summer, the excess flux of nitrate out of the Red Sea is estimated as 0.74 x106 tons of nitrogen ry-1. It is suggested that this excess of the combined nitrogen results from nitrogen fixation, presumably by Trichodesmium spp. It is estimated that nitrogen fixation may contribute up to 6% of the total primary production in the Red Sea.