Net Sea–Air CO$_{2}$ Fluxes and Modeled Partial Pressure of CO$_{2}$ in Open Ocean of Bay of Bengal

The key role of oceans in the global climatic system can be accurately quantified by the measurement of CO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> exchange across air–sea interface. The direction and magnitude of this CO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> exchange are mainly governed by the gradient of partial pressure of carbon dioxide (pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>) at the air–sea interface. The sea surface pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> is highly variable, primarily regulated by seasonal sea surface temperature (SST) and CO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> (aqueous) concentration. In this paper, the moored pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> observations from autonomous pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> system deployed at 15 <inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>N 90 <inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>E in the Bay of Bengal (BOB) were used to derive CO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> fluxes to examine variability over time scale at BOB. An attempt has also been made to develop a model using multiple linear regression (MLR) and support vector regression (SVR) to estimate the sea surface pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> from space-based observations of SST and salinity. pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> variability was primarily attributed to SST and CO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> concentration changes. Derived fluxes showed that BOB is a net annual source (0.440 g-C/m<inline-formula><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula>/year for year 2014) of CO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> at mooring location with significant seasonality effects. For the estimation of surface pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>, SVR model showed better results [root mean square error (RMSE) = 7.68 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>atm] in comparison to MLR model (RMSE = 12.36 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>atm). The seasonal climatological pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> maps from September 2011 to February 2018 showed southward increase in pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> in all seasons possibly due to southward increase in SST and less influence of river water. These pCO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> maps can further be utilized in deriving CO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> flux maps for BOB.