Water Transport Mechanisms in Earth's Mantle

Water enters Earth’s interior primarily through subducting oceanic plates that carry hydrous minerals and sediments into the mantle. In the upper mantle and transition zone, minerals such as wadsleyite and ringwoodite can host up to a few weight per cent of water in the form of hydroxyl groups. At depths beyond 600 km, water is incorporated into dense hydrous magnesium silicate phases (notably phase D and phase H), which remain stable under high‐pressure and high‐temperature conditions. Dehydration reactions at the top of the lower mantle may liberate fluids that modify melting behaviour and contribute to deep‐mantle metasomatism. Hydrogen‐bond symmetrisation in aluminous hydrous phases alters elastic and transport properties, influencing seismic wave speeds and electrical conductivity. Redox reactions under extreme pressures can further mobilise hydrogen and oxygen, feeding back into the redox state of Fe-bearing minerals and affecting the deep water cycle. Together, these processes shape mantle rheology, convection patterns and the long‐term evolution of Earth’s volatile budgets.

Research from Nature Portfolio

Advanced machine‐learning approaches have been used to predict electronegativity and work‐function changes of minerals under varying pressures, revealing how pressure‐driven electron delocalisation enhances redox reactivity between Fe(II)-bearing phases and water in subducting slabs. Such insights clarify the physicochemical drivers of water transport and its impact on deep electrical conductivity anomalies. High‐pressure nuclear magnetic resonance studies have directly monitored hydrogen mobility in linear O–H ⋯ O bonds up to 90 GPa, identifying a critical oxygen–oxygen distance at which hydrogen mobility peaks as a precursor to bond symmetrisation. This finding unifies observations across diverse hydrous systems and refines our understanding of the pressure threshold for hydrogen localisation. Foundational crystallographic and elasticity measurements of dense hydrous magnesium silicate phase H demonstrate its stability above 30 GPa and reveal its sound-wave velocities and anisotropy. These results confirm that aluminous phase H can transport significant water into the deep lower mantle and contribute to seismic anisotropy in cold subducting slabs.

Water Transport Mechanisms in Earth's Mantle publication trend

The graph below shows the total number of articles in water transport mechanisms in earth's mantle across all publications each year (not limited to Nature Index journals).

Technical terms

Hydrous mineral: A silicate phase whose crystal structure incorporates hydroxyl groups or molecular water.

Subduction zone: A convergent plate boundary where oceanic lithosphere descends into the mantle, transporting water and volatiles.

Transition zone: The mantle layer between ~410 km and ~660 km depths, characterised by phase transformations of olivine.

Dense hydrous magnesium silicate (DHMS): High-pressure phases (e.g., phase D, phase H) capable of storing water deep within the mantle.

Hydrogen-bond symmetrisation: The pressure-induced transition in O–H ⋯ O bonds where the proton becomes centred between two oxygen atoms, altering physical properties.

Bridgmanite: The perovskite-structured (Mg,Fe)SiO₃, the most abundant mineral in the lower mantle, which can incorporate water as hydroxyl defects.

References

1. The stability of hydrous silicates in Earth's lower mantle: Experimental constraints from the systems MgO–SiO2–H2O and MgO–Al2O3–SiO2–H2O. Chemical Geology (2015).
2. Electron transfer rules of minerals under pressure informed by machine learning. Nature Communications (2023).
3. Structural independence of hydrogen-bond symmetrisation dynamics at extreme pressure conditions. Nature Communications (2022).
4. Crystal structure, equation of state and elasticity of phase H (MgSiO4H2) at Earth’s lower mantle pressures. Scientific Reports (2015).
5. Volatiles in the mantle transition zone and their effects on big mantle wedge systems. National Science Review (2024).
6. Water Concentration in Single‐Crystal (Al,Fe)‐Bearing Bridgmanite Grown From the Hydrous Melt: Implications for Dehydration Melting at the Topmost Lower Mantle. Geophysical Research Letters (2019).
7. The role of water in Earth's mantle. National Science Review (2019).
8. Altered chemistry of oxygen and iron under deep Earth conditions. Nature Communications (2019).