The processes of production and burial of calcium carbonate sediments link Earth's climate and carbon cycle over geological timescales. Climate and atmospheric CO 2 influence the carbonate chemistry of seawater, which in turn influences the production and preservation of carbonate sediments (Berner et al., 1983). Reconstructing the carbonate chemistry of ancient seawater using observations from the sedimentary record enables understanding of the interactions between climate and carbon cycling in deep time, yet achieving this goal has remained elusive. Seawater carbonate chemistry can be characterized by six variables: partial pressure of CO 2 , pCO 2 ; bicarbonate ion concentration, [HCO 3 − ]; carbonate ion concentration, [CO 3 2− ]; total concentration of dissolved inorganic carbon (DIC) species, [DIC]; alkalinity (Alk); and pH (Zeebe & Wolf-Gladrow, 2001). Two of these variables must be known in order to solve the system of equations for the remaining unknowns. Calcite and aragonite mineral saturation states (Ω Ca and Ω Ar , respectively) link seawater carbonate chemistry with the thermodynamic driving force behind the abiotic or biologically mediated precipitation or dissolution of carbonate minerals:, where γCa 2+ and γCO 3 2− are the activities of the calcium and carbonate ions, respectively, and K sp is the mineral equilibrium solubility product.