Limited water incorporation in davemaoite under lower-mantle conditions

Water storage in Earth’s mantle impacts its physical and chemical properties, yet the capacity of the lower mantle to host water remains poorly constrained. While the transition zone is a major reservoir, the dominant lower-mantle minerals bridgmanite and ferropericlase exhibit limited water solubility, and the role of davemaoite (CaSiO3-perovskite) remains uncertain due to experimental challenges. Here we report in-situ lattice-volume measurements of davemaoite synthesized under dry and hydrous conditions up to 30 GPa and 2100 K using advanced multi-anvil techniques. At lower-mantle temperatures, hydration produces only a marginal volume reduction, indicating that water incorporation is limited to trace levels rather than the substantial amounts suggested previously. We also find no clear evidence for the tetragonal structure regardless of hydration. These results indicate that davemaoite stores limited water in the peridotitic mantle, implying that subducted crustal materials such as basaltic crust containing hydrous silica phases could dominate deep-lower mantle water storage. Davemaoite can store limited water in the lower mantle, suggesting that subducted materials like basaltic crust and sediments may serve as important water reservoirs, according to in-situ lattice volume measurements of davemaoite under dry and hydrous conditions.