Seismically invisible water in Earth's transition zone?

• Published in: Earth and planetary science letters 2018-09, Vol.498, p.9-16
• Main Authors: Schulze, Kirsten, Marquardt, Hauke, Kawazoe, Takaaki, Boffa Ballaran, Tiziana, McCammon, Catherine, Koch-Müller, Monika, Kurnosov, Alexander, Marquardt, Katharina
• Format: Article
• Language: English
• Subjects: Brillouin spectroscopy; elasticity; high-pressure; hydration; ringwoodite; transition zone
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2018.06.021

Ringwoodite, the dominant mineral at depths between 520 km and 660 km, can store up to 2–3 wt.% of water in its crystal structure, making the Earth's transition zone a plausible water reservoir that plays a central role in Earth's deep water cycle. Experiments show that hydration of ringwoodite significantly reduces elastic wave velocities at room pressure, but the effect of pressure remains poorly constrained. Here, a novel experimental setup enables a direct quantification of the effect of hydration on ringwoodite single-crystal elasticity and density at pressures of the Earth's transition zone and high temperatures. Our data show that the hydration-induced reduction of seismic velocities almost vanishes at conditions of the transition zone. Seismic data thus agree with a wide range of water contents in the transition zone. •A novel multi-sample loading technique for single-crystal HP Brillouin spectroscopy.•Elastic properties of four ringwoodite samples were measured simultaneously at HP/HT.•The aggregate velocities of ringwoodite are independent of the hydration state at HP.•Water in the transition zone might not be detectable by seismic wave speed variations.