Intensive observations in the northeast Indian Ocean (Bay of Bengal) during the pre-southwest and northeast monsoon seasons of 1991 reveal that freshwater discharge from rivers of the Indian subcontinent exerts the dominant control over total carbon dioxide (TCO2) and pCO2 distributions in surface waters. Low pCO2 levels occur within the low-salinity zones, with a large area in the northwestern bay acting as a sink for atmospheric CO2. Only a part of the observed pCO2 variation can be accounted for by the effect of salinity, and biological production supported by external nutrient inputs in conjunction with strong thermohaline stratification may be more important in lowering surface water pCO2 by >100 μatm relative to that in the atmosphere. The pCO2 distribution is seasonally variable and appears to be controlled by the spreading of fresher waters by the prevailing surface circulation. ¿ American Geophysical Union 1996