Estimation of Air-Sea CO 2 Exchange and Decadal Change of Surface Water f CO 2 in a Shallow Continental Shelf Using in Situ and Remote Sensing Data During Winter

The air-sea CO2 exchange (fCO2) was estimated in the outer estuary to offshore transition zone of the northern Bay of Bengal using in situ measurements and remote sensing data obtained from moderate resolution imaging spectroradiometer (MODIS) and advanced very high resolution radiometer (AVHRR). The in situ measurements were done during winter months (December, January and February) of the year 2011–12. Sea surface CO2 fugacity (fCO2), sea surface temperature (SST) and chlorophyll-a were measured in situ to develop an empirical relationship with fCO2 but only the SST showed a significant correlation (r 2 = 0.55, n = 64, p < 0.05). This relationship was used to assess fCO2 (water) and its temporal change in decadal scale from the year 2002–2003 to 2011–2012 of the winter months using remotely sensed SST data. The study area acted as a mild sink for atmospheric CO2 at the mean rate of −28 µmol m−2 h−1 (MODIS derived) to −40 µmol m−2 h−1 (AVHRR derived). An overall winter-to-winter increasing trend of fCO2 was observed in the last decade which is accompanied by a similar decrease in the chlorophyll-a concentrations.