Study on oxygen and phosphate in the waters of the southern Arabian Gulf and the Gulf of Oman

Abstract

     Sea water samples were collected from 35 stations in the southern Arabian Gulf and the Gulf of Oman during winter of 1987. In the southern Arabian Gulf dissolved oxygen shows an increase in an offshore direction at a rate of 1.3-5.7 x 10^-3 ml. l^-1. km^-1 as ell as strong corre­lation exists (r=-0.71) between oxygen and temperature. The presence of detectable phosphate in surface waters at vitrually all stations both in the southern Arabian Gulf (0.12-0.84 µmoles l^-1) and the Gulf of Oman (0.18-1.65 µmoles l^-1) may indicate that phosphate if not a limiting factor.

      The presence of a shallow oxygen minimum (0.23-0.79 ml. l^-1 & 4.2-15.9%) that coincides with the layer of ma­ximum phosphate (1.06-2.64 µmoles l^-1) at a depth of 100-200 meters results from the mineralization of organic matter. The identification of water mass of Arabian Gulf origin that exhibits higher levels of temperature (20.10-21.54°C), salinity (37.06-38.11%) and oxygen (1.40-2.09 ml. l^-1) at a depth of 200-350 meters was performed.

     The estimated ratio of AOU: PO₄ in the Omani water is found to be 250 compared with 167 in the southern Ara­bian Gulf which represent about 40% less than the theo­retical value of Redfield.

     The excess of oxygen remaining after the oxidation of all organic matter in the layer of minimum oxygen is found to be 30% of saturation. Of this amount, 20% is con­sumed in processes other than oxidation of organic matter.

     The phosphate budget in the Arabian Gulf is evaluated as 375 x10² tonnes year^-1 which represent the net gain to the Gulf water.