Distributions of total alkalinity (TA), dissolved inorganic carbon (DIC), and other parameters relevant to the marine inorganic carbon system were investigated in shelf and adjacent ocean waters during a U.S. Gulf of Mexico and East Coast Carbon cruise in July–August 2007. TA exhibited near-conservative behavior with respect to salinity. Shelf concentrations were generally high in southern waters (Gulf of Mexico and East Florida) and decreased northward from Georgia to the Gulf of Maine. DIC was less variable geographically and exhibited strongly nonconservative behavior. As a result, the ratio of TA to DIC generally decreased northward. The spatial patterns of other CO₂ system parameters closely followed those of the TA : DIC ratio. All sampled shelf waters were supersaturated with respect to aragonite (saturation state Ω_A > 1). The most intensely buffered and supersaturated waters (Ω_A > 5.0) were in northern Gulf of Mexico river-plume waters; the least intensely buffered and least supersaturated waters (Ω_A < 1.3) were in the deep Gulf of Maine. Due to their relatively low pH, Ω_A, and buffer intensity, waters of the northeastern U.S. shelves may be more susceptible to acidification pressures than are their southern counterparts. In the Mid-Atlantic Bight, alongshore mixing tended to increase DIC concentrations southward, but this effect was largely offset by the opposing effects of biogeochemical processing. In the Gulf of Mexico, downstream increases in Loop Current DIC suggested significant contributions from shelf and gulf waters, estimated at 9.1 × 10⁹mol C d⁻¹. Off the southeastern U.S., along-flow chemical changes in the Florida Current were dominated by mixing associated with North Atlantic subtropical recirculation.