A new study is reshaping how scientists think about Earth’s deep water cycle. In lower-mantle conditions, Ishii and colleagues report that davemaoite—a magnesium-rich mineral thought to exist at extreme depths—does not eagerly take up water. The result challenges the idea that the mantle’s interior could store large amounts of hydrogen just by forming water-tolerant minerals.
Davemaoite is considered an important host phase in the lower mantle because its crystal structure can, in principle, incorporate hydrogen-bearing species. Such incorporation would occur through substitutions inside the lattice, potentially linking water to the mantle’s long-term storage and release mechanisms. But the new findings indicate that this mineral’s capacity for water is “limited,” meaning less hydrogen can be trapped than expected under comparable conditions.
To reach this conclusion, the team investigated how davemaoite responds to simulated lower-mantle environments. They combined experimental constraints with analysis of hydrogen incorporation behavior, focusing on whether water-related defects can form efficiently. The study emphasizes that lower-mantle pressure and temperature do not automatically guarantee substantial hydration in all candidate minerals.
The researchers argue that the lattice chemistry and the energetic cost of inserting water-related defects likely suppress hydrogen uptake. In other words, while hydrogen can be incorporated under some circumstances, the equilibrium under deep-mantle conditions favors only small amounts. This helps explain why certain deep-mantle reservoirs may remain relatively dry despite Earth’s overall water inventory.
Their interpretation carries implications for modeling Earth’s interior. If davemaoite cannot store large water quantities, then other phases—such as hydrous minerals stable at different depths, or scenarios involving transient melt/fluid transport—may need to account for most of the hydrogen budget.
The work also affects how scientists interpret geophysical observations. Seismic signatures and mantle convection models depend on mantle composition and water content, both of which influence mineral rheology and melting behavior. Limited hydration in davemaoite would shift expectations for viscosity and deformation in the lower mantle.
Finally, the study underscores how minerals can behave very differently across pressure-temperature regimes. Water incorporation is governed not only by mineral presence, but by defect formation energetics and structural constraints at depth. The message is clear: deep-mantle hydration may be far more selective than previously assumed.
Subject of Research: Limited water (hydrogen) incorporation in davemaoite under lower-mantle conditions.
Article Title: Limited water incorporation in davemaoite under lower-mantle conditions.
Article References: Ishii, T., Takaichi, G., Nishihara, Y. et al. (2026). Communications Earth & Environment. https://doi.org/10.1038/s43247-026-03856-7
