A sink for atmospheric carbon dioxide in the northeast Indian Ocean

Abstract

Intensive observations in the northeast Indian Ocean (Bay of Bengal) during the presouthwest 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.