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

Abstract

Air-water CO₂ flux was measured from the gradient of <i style="">f</i>CO₂ (water) and <i style="">f</i>CO₂ (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. <i style="">f</i>CO₂ (air) ranged between 275.08 µatm to 459.07 µatm and <i style="">f</i>CO₂ (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 CO₂ 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 <i style="">f</i>CO₂ and pH reflects a possible influence of biological activity as well. A maximum efflux rate of 24.56 µmol m^-2 h^-1and 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.