Mineral-bound H2O solubility maps applied to Earth-like global mantle convection models

The amount and distribution of water within Earth’s mantle remain uncertain, largely due to limited observational constraints and the only moderately constrained water capacities of primary lower mantle minerals. Recent advances in experimental and theoretical determinations of H₂O solubilities, however, now enable a more direct integration of these constraints into geodynamic models, offering new insights into Earth’s deep water cycle. Here, we employ Gibbs free energy minimization over a broad range of pressure–temperature conditions, combined with published H₂O solubility measurements, to generate mineral-bound mantle H₂O storage capacity maps as a function of phase equilibria. These maps—along with tables documenting density variations in nominally anhydrous minerals arising from water incorporation—are accessible through a customizable and parallelized Julia script.

Incorporating these storage capacity maps into a 2D mantle convection model (StagYY) yields outcomes consistent with existing literature. The simulations suggest that, throughout Earth’s history, the transition zone harbors a heterogeneous 0.2–0.5 wt% water content. Deeper in the mantle, water transport is controlled by the presence of dense hydrous magnesium silicates in subducting slabs. In their absence, descending material quickly dehydrates while exiting the wadsleyite–ringwoodite stability field, before H₂O solubility increases again under CaCl₂-type stishovite conditions (~50–60 GPa). Nevertheless, slow mantle convection and weak diffusivity enable any deeply emplaced water to persist at great depths. Over 4.5 Gyr of Earth-like evolution, an aquaplanet simulation retains roughly four to five ocean masses of water in the planetary interior, depending on the efficiency of water migration within the mantle. Simplified 3D models coupled with plate reconstructions further elucidate the dynamic balance of water influx and efflux over the Phanerozoic, providing an integrated view of the mantle’s evolving water budget.