Extensive observations have been made on the carbon dioxide system in the Arabian Sea during three different seasons as part of the Indian Joint Global Ocean Flux Study (JGOFS) Programme. Concentrations of total carbon dioxide and partial pressure of carbon dioxide exhibited seasonal variability, with pronounced north-south gradients in surface layers. Total carbon dioxide in surface waters was higher by approx 100 mu M during winter compared to the intermonsoon period due to winter cooling and convective mixing. The partial pressure of carbon dioxide (pCO sub(2)) in surface layers was generally in excess over the atmospheriec value, suggesting that the central and eastern Arabian Sea is a perennial source to atmospheric carbon dioxide. The flux of carbon dioxide to atmosphere reached a maximum of approx 40 m mole m sup(-2) d sup(-1) around 16 degrees N in the central Arabian SEa during monsoon season. The carbon dioxide regenerated from soft tissue was higher during winter and is the least in monsoon. The aragonite saturation horizon occurred around 500 m.