The dissolution of carbon dioxide in water and the ensuing hydrolysis reactions are of profound importance for understanding the behavior and control of carbon in the terrestrial environment. The first X-ray absorption spectra of aqueous carbonate have been measured at three different pH values to characterize the evolution of electronic structure of carbonate, bicarbonate, carbonic acid and dissolved CO2. The corresponding carbon K-edge core-level spectra were calculated using a first-principles electronic structure approach which samples molecular dynamics trajectories. Measured and calculated spectra are in excellent agreement. Each species exhibits similar, but distinct, spectral features which are interpreted in terms of the relative C-O bond strengths, molecular configuration, and hydration strength. (C) 2011 Elsevier B. V. All rights reserved.