Processes controlling carbon components in the Arabian Sea

Abstract

Data on carbon dioxide components, collected just before SW monsoon 1986, have been analysed. Total carbon dioxide (TCO 2 ) and titration alkalinity are higher in the northern and western Arabian Sea compared to those in the southern and eastern regions, while the concentrations are the highest in the northern part. Maximum TC0 2 of about 2650 µmol. dm -3 was found in near bottom layers at 2O°N. Incursion of Red Sea Water around 12°N resulted in the deepening of carbon dioxide lsopleths above the levels of 2300 µmol dm -3 . TCO 2 relations with apparent oxygen utilization and phosphate suggest a northward decrease in carbon dioxide production per unit oxygen consumption. Despite the high biological production in the western Arabian Sea, relatively low CaCO 3 dissolulion (∼100 mol dm -3 near and below 3000m) is attributed to skeletal material incorporation into faecal material and the subsequent faster deposition rates. Arabian Sea water is found to be undersaturated around 200- 400m and 200-600m with respect to aragonite and calcite, respectively. Carbon dioxide added through regeneration processes exceeds 500 µmol dm -3 around 20°N, a part of which is transported towards south. Enhanced pCO 2 build up towards north, to maximum of 1000 µatm, results in increased CO 2 transport from sea to air-from south to north. Arabian Sea seems to be a CO 2 source for the atmosphere since the fraction of CO 2 in air, calculated based on CO 2 concentration in seawater, is more than 0.5. Although, the Persian Gulf Water and the Rei Sea Water influence could be seen from preformed CO 2 levels in the Arabian Sea, the quantum of respective anthropogenic contributions could not be ascertained in view of the large uncertainties involved.