Water in the Earth's lower mantle

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The most vital component of the Earth is water. It is not only the source of life, but also the key ingredient controlling a wide range of solid earth processes, such as the operation of plate tectonics, the formation of volcanoes, and the emergence of continents. Plate tectonics and volcanic eruptions lead to the active exchange of surface water and interior water, regulating the variation of ocean volumes and continent areas throughout the Earth’s history. Despite its importance, in present-day the Earth’s surface water accounts for only 0.02 percent of the planet’s total mass. Most of the Earth’s water is instead thought to be present in the Earth’s deep interior, but the exact amount of water stored in the Earth’s interior remains largely unknown. This proposal will rigorously study the water solubility in bridgmanite, the most abundant material of the deep mantle. This will be accomplished by using large-scale computer simulations of bridgmanite and fluid in coexistence, using the latest innovations in machine learning. The calculations will be referenced to results derived from high-precision calculations based in quantum mechanics. This work will support the training of graduate students in cutting-edge computational techniques using high-performance computing centers. Water solubility in the mantle is a fundamental material property that quantifies the maximum amount of water that can be hosted within the Earth. Large-scale two-phase simulations of bridgmanite and fluid coexistence driven by machine learning potentials of ab initio quality will be carried out to rigorously study the water solubility in bridgmanite. These simulations will reveal: 1) the solubility of water in bridgmanite and the effects of Fe and Al across the entire lower mantle; 2) the hydrogen incorporation mechanisms as a function of pressures, temperatures, and bulk chemistry; 3) the bridgmanite-water (pseudo)-binary phase diagrams; and 4) the evolutionary history of the water storage capacity of the lower mantle over the past 4.5 billion years. This project is co-funded by the Directorate for Geosciences to support AI/ML advancement in the geosciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.