Comprehending the role of different mechanisms and drivers affecting the sea-surface pCO2 and the air-sea CO2 fluxes in the Bay of Bengal: A modeling study

We apply a coupled physical and biogeochemical (ROMS+PISCES) to understand the influence of distinct drivers and mechanisms on the sea-surface pCO2 and the air-sea CO2 flux of the Bay of Bengal (BoB). The model evaluation suggests that the model simulated sea-surface pCO2 is in accord with the observations. The north of BoB is found to be a sink for the atmospheric CO2, whereas the rest of the region acts as a source. The effect of dissolved inorganic carbon (DIC) and the total alkalinity (TALK) is found to be predominant but is contrasting in nature. Mixing-induced changes in DIC and TALK results in high pCO2 (+570μatm) and, consequently, the positive CO2 flux. The biological activity does draw down the surface pCO2 (−120μatm) but is insufficient in completely opposing the effect of mixing. The uptake of CO2 in the north is due to the CO2 solubility, which is a function of salinity and temperature. The northern rivers, having a high discharge rate, reduce the salinity and temperatures in the north, which possibly aids in this region to be a sink. In the northeast monsoon season, the impact of temperature and DIC is high and opposing. The TALK reduces the pCO2 in the northeast monsoon, but the magnitude is low. The pCO2 in the southwest monsoon is influenced primarily by temperature, whereas in the postmonsoon monsoon, the freshwater dominates. The pre-monsoon season experiences the TALK, temperature, and freshwater increase the pCO2 anomalies, and only the DIC reduces pCO2 anomalies. •The northern Bay of Bengal (BoB) is a sink of CO2.•Circulation is the assertive mechanism driving sea-surface pCO2 variability.•Biology and solubility oppose but do not cancel the circulation effect.•The DIC and TALK cancel out each other's effect.•Freshwater flux dominates the region's source and sink characteristics.