Bicarbonate

Bicarbonate (HCO3-) is the dominant form of dissolved inorganic carbon in seawater, making up roughly 90 percent of the total at a typical surface pH near 8.1. It sits between dissolved CO2 and carbonate ion in the carbonic-acid equilibria, so its share rises as pH falls. Because the bicarbonate-carbonate pair buffers seawater, added CO2 reacts with carbonate ion to form bicarbonate, which lowers carbonate-ion concentration and drives ocean acidification. The Revelle factor near 10 quantifies how this buffering limits the ocean uptake of anthropogenic CO2.