Chemical oceanography of the Persian Gulf

Abstract

Measurements of basic hydrographic properties, nutrient elements, alkalinity and total carbon dioxide were made in the Persian Gulf in February and March 1977, on R.V. Atlantis II Cruise 93. The results show clearly the penetration into the Gulf of surface Indian Ocean water, initially of 36.5% salinity which is carried northwards along the Iranian Coast, gradually increasing in salinity to more than 40%. The inflowing surface water is high in phosphate (1.0-0.5 μmoles kg −1) due to upwelling induced by the north-east monsoon. However, nitrate levels are at, or below, the detection limit and nitrogenous nutrients appear to be limiting. The seawater carbonate system is greatly perturbed by the precipitation of large quantities of calcium carbonate. The alkalinity-salinity relationship shows that the greatest carbonate loss occurs in the shallow waters of the Trucial Coast, where up to 125 μmoles kg −1 of CaCO 3 have been lost from the water. Dense, saline low specific alkalinity water formed in the shallows appears to migrate down slope to augment the outflowing waters in the deeper part of the Gulf. The outflow of the Tigris, Euphrates and Karun rivers to the north provides an intense, but low capacity signal, of low salinity, high specific alkalinity, waters. Large amounts of CO 2 are also fixed by photosynthetic processes. The classical Mediterranean type of circulation is plainly revealed. The residence time of water within the Persian Gulf is approximately 2.5 yr.