East India Coastal Current controls the dissolved inorganic carbon in the coastal Bay of Bengal

Abstract

Monthly variations in dissolved inorganic components (DIC) were measured in the coastal waters off Visakhapatnam in the western Bay of Bengal (BoB) to examine the controlling factors on their distribution and fluxes to the atmosphere. The seasonal variations in the direction of East India Coastal Current (EICC) bring significant variations in the hydrographic properties in the coastal western Bay. Poleward moving EICC from February to May brings in high saline waters to the study region resulting in weak stratification and the coastally trapped upwelling Kelvin Waves aid coastal upwelling. On the other hand, equatorward flowing EICC from October to December brings in low saline, warm waters to the study region resulting in strong stratification, and contributes to lower concentrations of DIC and partial pressure of carbon dioxide (pCO2) and higher pH. During March-August period, higher concentrations of DIC and pCO2 and lower pH were observed due to upwelling of subsurface waters under the influence of an shoreward approaching cyclonic eddy. The DIC, pH and pCO2 displayed significant relations with temperature, salinity and chlorophyll-a in the both inshore and offshore region. Biological processes are dominant over mixing effect during March-August in both inshore and offshore regions, while their impact decreases towards offshore. Similarly thermal effect is higher during March-August and salinity effect is significantly higher during October-December when the EICC brings in freshwaters from the northern Bay. It is also noticed that the impact of fluxes variations is significantly low. This study suggests that the physical processes modulate the biological processes significantly to influence the DIC system in the coastal BoB and makes it as a strong source for atmospheric CO2 than hitherto hypothesized to be a sink.