The carbonate system of water of the inner estuary and near shore in the Mahanadi estuary, Bay of Bengal, India was studied in summer season of 2014. Physicochemical parameters like temperature, pH, salinity, total alkalinity (TA), dissolved inorganic carbon (DIC), total organic carbon (TOC) and chlorophyll a (chl a) were measured in order to study their role in controlling the CO 2 flux. The estuary acted as a sink for atmospheric CO 2 triggered by the allochthonous organic carbon input. The

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... erage CO 2 flux was recorded as -0.36±13.29 µmol/m 2 h in inner estuary and -10.36±2.00 µmol/m 2 h in near shore region. The temperature and salinity were found to be significantly and positively correlated with fCO 2 (water) indicating their deterministic role in influencing air-water CO 2 flux.