Inorganic carbon parameters were studied for the first time in the Mississippi River estuary and plume. Area-integrated biological uptake rates (1.5--3 gC m-2 d-1) derived from riverine total dissolved inorganic carbon (DIC) and total alkalinity (TAlk) fluxes as well as that based on the consumptions of DIC and TAlk in the plume are comparable to earlier results of 14C incubation in individual water samples. This rate is among the highest in the estuaries and plumes of the world's largest rivers. Fluvial DIC flux (13.5 ¿ 1012 gC yr-1) indicates a 16% increase in the inorganic carbon flux over the earlier estimate and perhaps an increase in the weathering rate in the Mississippi River basin over the past four decades.