Seasonal quantification of carbonate dissolution and CO2 emission dynamics in the Indian Sundarbans estuaries

Shifts in carbonate dissolution can help understand the exchange of carbon dioxide between the air and water of estuarine systems. Adequate spatial coverage is required to understand these emission dynamics. Hence, the distribution of carbonate parameters in three estuaries covering a vast expanse of the Indian Sundarbans is described from total alkalinity (TA), dissolved inorganic carbon (DIC) and pH data collected between 2016 and 2020. The seasonal impacts on inorganic carbon parameters were also studied by comparing pre-monsoon, monsoon, and post-monsoon data compiled from the study period. The estuaries showed the highest TA (up to 2506μmol kg −1) and DIC (up to 2203μmol kg −1) in the pre-monsoon. Both the parameters overall were positively associated with salinity. TA and DIC decreased by 369 and 208μmol kg −1, respectively, in the monsoon compared to pre-monsoon. From the monsoon to the post-monsoon, TA and DIC increased by 121 and 85μmol kg −1, respectively. Both showed strong positive associations with high chlorophyll- a and high dissolved oxygen in the post-monsoon suggesting an important role of primary production in the estuaries in raising the concentrations of inorganic carbon parameters. The carbonate mineral saturation states (ΩCa and ΩAr) followed the same pattern as that of TA and DIC. The pair was always supersaturated although freshwater influence caused the values to drop to close to saturation. While pCO2 was mostly supersaturated in the system relative to atmospheric concentration, it became minimal in the post-monsoon corresponding to heightened primary production. Despite high organic carbon recycling in mangroves, the system showed less expression in terms of CO2 emission in a seasonal cycle. Overall, the Indian Sundarbans estuarine system emitted low amounts of CO2 with its estimated water-to-air flux densities varying from 0.40 ± 0.61 (pre-monsoon) to 1.62 ± 1.74 mmol m−2h−1(monsoon).

Acharya A., Sanyal P., Paul M., Gupta V. K., Bakshi S., Bhattacharyya P. & Mukhopadhyay S. K., 2022. Seasonal quantification of carbonate dissolution and CO2 emission dynamics in the Indian Sundarbans estuaries. Regional Studies in Marine Science: 102413. doi: 10.1016/j.rsma.2022.102413. Article (subscription required).

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