Dr. Hideharu Kuwabara, a lecturer at GRC, joined the research group led by Associate Professor Masayuki Nishi at the Graduate School of Science, Osaka University, and discovered a new mechanism by which water inside the Earth slows down seismic wave velocities in the deepest mantle.
At the boundary between the Earth’s liquid iron core and the overlying mantle, known as the core-mantle boundary (CMB) at a depth of 2,900 km, there are special regions called ultra-low velocity zones (ULVZs) where seismic waves travel extremely slowly. Previously, it was hypothesized that iron elements migrating from the core into the mantle caused this velocity reduction, but the mechanism by which iron moves within the mantle remained a significant mystery.
In this study, experiments simulating the high-temperature and high-pressure conditions inside the Earth confirmed that water reacts with iron to form new minerals, enabling rapid iron transport within those minerals. This finding suggests that the presence of water in the mantle contributes to the formation of ULVZs. Furthermore, it was estimated that approximately 3 × 10¹⁹ tons of water (about 20% of the Earth’s total seawater) would be required to form such regions.
This discovery strongly suggests that surface water cycles through the mantle and even reaches the core, offering a new perspective on Earth’s evolution and internal structure.
The research results were published in the British scientific journal “Nature Communications” (online).
Extensive iron–water exchange at Earth’s core-mantle boundary can explain seismic anomalies
Katsutoshi Kawano, Masayuki Nishi, Hideharu Kuwahara, Sho Kakizawa, Toru Inoue and Tadashi Kondo
doi：10.1038/s41467-024-52677-9