Water Reservoirs in the Lower Mantle Beneath Northeastern Asia

Water in the mantle controls mantle convection and chemical transport processes within Earth's interior. However, whether the water in the lower mantle is primordial or recycled remains an open question. Here we report an electrical structure consisting of two stepped high-conductivity anomalies crossing the 660-km interface beneath northeastern Asia. The sheet-like first-step conductor locates in the mantle transition zone that can be best interpreted as hydrated stagnant Pacific slab, whereas the funnel-like second-step anomaly occurs in the uppermost lower mantle that is inferred to be a water reservoir replenished by the collapsed stagnant slab. The pivotal mechanism of this water transport process could be the dehydration reaction of dense hydrous magnesium silicates and the rehydration of stishovite and liebermannite in the transition zone. Our findings provide evidence for recycled lower-mantle water reservoirs, and together with seismological and mineralogical studies, illustrate the deep-mantle water plumbing system operated by cold slab subduction.