Hydrous phases in the Earth's lower mantle
Water provides the foundation for life on planet Earth and drives the geological processes that shape the Earth's surface. Plate tectonics, in turn, links the Earth's surface to its deep interior and supplies water to a deep H2O cycle that may extend into the lower mantle at depths in excess of 660 km. The H2O circulating in this deep H2O cycle may act as a deep H2O reservoir that likely helped to stabilise the oceans and atmosphere throughout the geological past and hence to maintain habitable conditions on the Earth's surface. The contribution of the lower mantle to the deep H2O cycle, however, remains highly uncertain although the lower mantle comprises 49.2 % of the Earth's mass. Even minor amounts of H2O stored in the rocks of the lower mantle may therefore have a significant impact on the Earth's water budget.
The project HYDROSPHEAR will explore how H2O may be stored in hydrous minerals of the lower mantle by constraining their stability limits and physical properties. The stability limits of the hydrous compounds phase D and phase H will be determined by sampling their melting reactions at high pressures in laser-heated diamond anvil cells. In addition, we will use Brillouin spectroscopy to determine the elastic properties of phase D and phase H at high pressures and high temperatures. The results of these measurements will be integrated into a systematic search for hydrous rocks in the lower mantle by analysing seismic observations. By providing critical information on the properties of hydrous phases in the lower mantle, HYDROSPHEAR may reshape our image of the Earth's deep H2O cycle.
Funding agency & programme: European Research Council (ERC), Horizon Europe
Funding period: 2026–2030 (prospective)
Funding volume (in Euro): 1.5 million
Principal investigator & host institution: Johannes Buchen, Universität Bayreuth
© Johannes Buchen 2022–2025. Imprint.