Air - water carbon dioxide exchange dynamics along the outer estuarine transition zone of Sundarban, northern Bay of Bengal, India

Air-water CO ₂ flux was measured from the gradient of fCO ₂ (water) and fCO ₂ (air) in the Hooghly-Matla estuary to offshore transition zone. An average gas transfer velocity of 10.2 cm h ^-1 was evaluated in this region. fCO ₂ (air) ranged between 275.08 μatm to 459.07 μatm and fCO2 (water) varied from 149.1 μatm to 299.2 μatm. Wind velocity and bathymetry (depth) were observed to be the main controlling factors for exchange of CO ₂ between the atmosphere and water phase. Seawater is found to have a greater influence at the marine end of the estuary. Apart from physical mixing in this freshwater-sea water interacting zone, the study of fCO ₂ and pH reflects a possible influence of biological activity as well. A maximum efflux rate of 24.56 μmol m ^-2 h ^-1 and influx rate of -41.61 μmol m ^-2 h ^-1 is determined during high wind velocity. The overall region surveyed was found to behave as a sink during the study period with an average (daytime) influx rate of -14.03 μmol m ^-2 h ^-1.