Inorganic carbon speciation and fluxes in the Congo River

Seasonal variations in inorganic carbon chemistry and associated fluxes from the Congo River were investigated at Brazzaville-Kinshasa. Small seasonal variation in dissolved inorganic carbon (DIC) was found in contrast with discharge-correlated changes in pH, total alkalinity (TA), carbonate species, and dissolved organic carbon (DOC). DIC was almost always greater than TA due to the importance of CO2*, the sum of dissolved CO2 and carbonic acid, as a result of low pH. Organic acids in DOC contributed 11-61% of TA and had a strong titration effect on water pH and carbonate speciation. The CO2* and bicarbonate fluxes accounted for similar to 57% and 43% of the DIC flux, respectively. Congo River surface water released CO2 at a rate of similar to 109 mol m(-2) yr(-1). The basin-wide DIC yield was similar to 8.84 x 10(4) mol km(-2) yr(-1). The discharge normalized DIC flux to the ocean amounted to 3.11 x 10(11) mol yr(-1). The DOC titration effect on the inorganic carbon system may also be important on a global scale for regulating carbon fluxes in rivers. Citation: Wang, Z. A., D. J. Bienvenu, P. J. Mann, K. A. Hoering, J. R. Poulsen, R. G. M. Spencer, and R. M. Holmes (2013), Inorganic carbon speciation and fluxes in the Congo River, Geophys. Res. Lett., 40, 511-516, doi:10.1002/grl.50160.