Inorganic carbon speciation and fluxes in the Congo River

Abstract

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 CO 2 *, the sum of dissolved CO 2 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 CO 2 * and bicarbonate fluxes accounted for ~57% and 43% of the DIC flux, respectively. Congo River surface water released CO 2 at a rate of ~109 mol m -2 yr -1. The basin-wide DIC yield was ~8.84 × 10 4 mol km -2 yr -1. The discharge normalized DIC flux to the ocean amounted to 3.11 × 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. Key Points The carbonate chemistry near the Congo River mouth is comprehensively studied Organic acids have a titration effect on the inorganic carbon system Surface CO 2 and inorganic carbon fluxes to the ocean are characterized ©2013. American Geophysical Union. All Rights Reserved.