Seasonal controls on surface pCO(2) in the central and eastern Arabian Sea

The variability in partial pressure of carbon dioxide (pCO(2)) and its cont rol by biological and physical processes in the mixed layer (ML) of the cen tral and eastern Arabian Sea during inter-monsoon, northeast monsoon, and s outhwest monsoon seasons were studied. The hit varied from 80-120 m during NE monsoon, 60-80 m and 20-30 m during SW- and inter-monsoon seasons, respe ctively, and the variability resulted from different physical processes. Si gnificant seasonal variability was found in pCO(2) levels. During SW monsoo n, coastal waters contain two contrasting regimes; (a) pCO(2) levels of 520 -685 mu atm were observed in the SW coast of India, the highest found so fa r from this region, driven by intense upwelling and (b) low levels of pCO(2 ) (266 mu atm) were found associated with monsoonal fresh water influx. It varied in ranges of 416-527 mu atm and 375-446 mu atm during inter- and NE monsoon, respectively, in coastal waters with higher values occurring in th e north. The central Arabian Sea pCO(2) levels were 351-433, 379-475 and 38 5-432 mu atm during NE- inter and SW monsoon seasons, respectively. The mix ed layer pCO(2) relations with temperature, oxygen, chlorophyll a and prima ry production revealed that the former is largely regulated by physical pro cesses during SW- and NE monsoon whereas both physical and biological proce sses are important in inter-monsoon. Application of Louanchi et al (1996) m odel revealed that the mixing effect is the dominant during monsoons, howev er, the biological effect is equally significant during SW monsoon whereas thermodynamics and fluxes influence during inter-monsoons.