Role of river discharge and warming on ocean acidification and pCO2 levels in the Bay of Bengal

Abstract

Shifts in surface ocean pCO2 and pH are important controls governing global climate. Based on the linear relationship of observed surface pH and pCO2 with sea surface temperature (SST), sea surface salinity (SSS) and Chlorophyll-a (Chl-a) multiple linear regression equations were developed. Based on remote sensing SST, Chl-a and model-derived SSS, pH and pCO2 data were derived from 1998 to 2015. Overall warming of BoB is noticed at the rate of 0.004° to 0.03 °C/y whereas cooling is found in the northwestern BoB during winter and spring seasons associated with an increase in atmospheric dust. Decrease in SSS is noticed during all seasons due to melting of Himalayan ice cover associated with increase in fresh water flux due to increase in atmospheric temperature. Increase in pH is observed in the eastern and southern Bay during all seasons associating with warming and decrease in salinity. In contrast, decrease in pH (−0.001 y−1) and pCO2 increase (+0.1 to +0.7 µatm y−1) is noticed in the western and head Bay during winter and spring seasons due to deposition of atmospheric pollutants. This study suggests that increase in freshwater input due to melting of Himalayan ice cover and deposition of atmospheric pollutants are dominant controlling factors on surface ocean pH and pCO2 in the BoB between 1998 and 2015 and this region is acting as a stronger sink for the atmospheric CO2 in the present than that in the past two decades. The global coastal regions are significantly influenced by river discharge and atmospheric deposition of pollutants and they are not part of the global models leading to ill-reproduction of seasonal variability in pH and pCO2. Inclusion of these processes may improve prediction of pH and pCO2 in the regions heavily influenced by discharge/deposition from land and atmosphere.