Oxygen isotope composition of the Phanerozoic ocean and a possible solution to the dolomite problem

Significance The elemental and isotopic compositions of seawater have evolved throughout Earth’s history, in tandem with major climatic, tectonic and biologic events, including the emergence and diversification of life. Over geological timescales, the oxygen isotope composition of seawater reflects a global balance between mineral–rock reactions occurring at the Earth’s surface (weathering and sedimentation) and crustal (hydrothermal alteration) environments. We put constraints on the oxygen isotope composition of seawater throughout the Phanerozoic and demonstrate that this value has remained stable. This stability suggests that the fluxes of globally averaged oxygen isotope exchange, associated with weathering and hydrothermal alteration reactions, have remained proportional through time and is consistent with the hypothesis that a steady-state balance exists between seafloor hydrothermal activity and surface weathering.