Dominant Biological Control Over Upwelling on pCO2 in Sea East of Sri Lanka

Upwelling enhances pCO(2) levels due to injection of carbon-rich water to the surface despite the removal of carbon due to increase in primary production supported by enhanced nutrients. It is hypothesized that in the Bay of Bengal, upwelling may decrease pCO(2) due to existence of low saline and pCO(2)-poor waters in the subsurface layer. In order to test this hypothesis, a high-resolution state-of-the-art ocean biogeochemical model (Regional Ocean Modeling System) runs are examined at the sea east of Sri Lanka (SESL) where intense upwelling occurs during summer monsoon (May to August). Upwelling enhances pCO(2) by 34atm, whereas decrease in surface temperature and increase in surface salinity reduce pCO(2) by 24atm. The estimated net effect of upwelling is an increase in pCO(2) by 10atm. In contrast, soft and hard tissues together contribute to a decrease in pCO(2) by 21atm suggesting that the biological effect dominates over upwelling, resulting in a net decrease of pCO(2) by 11atm in the SESL. This striking contrast between the increase in pCO(2) due to physical dynamics (upwelling) and the removal of pCO(2) due to biological processes is caused by shallow (deep) nitracline (dissolved inorganic carbon-isoline) in the SESL.