title: Carbon-depleted outer core revealed by sound velocity measurements of liquid iron-carbon alloy.
abstract: The relative abundance of light elements in the Earth's core has long been controversial. Recently, the presence of carbon in the core has been emphasized, because the density and sound velocities of the inner core may be consistent with solid Fe7C3. Here we report the longitudinal wave velocity of liquid Fe84C16 up to 70 GPa based on inelastic X-ray scattering measurements. We find the velocity to be substantially slower than that of solid iron and Fe3C and to be faster than that of liquid iron. The thermodynamic equation of state for liquid Fe84C16 is also obtained from the velocity data combined with previous density measurements at 1 bar. The longitudinal velocity of the outer core, about 4% faster than that of liquid iron, is consistent with the presence of 4-5 at.% carbon. However, that amount of carbon is too small to account for the outer core density deficit, suggesting that carbon cannot be a predominant light element in the core.
authors.affiliation: Materials Dynamics Laboratory, RIKEN SPring-8 Center, RIKEN, Hyogo 679-5148, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Nakajima
authors.affiliation: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan.|Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan.
authors.forename: Saori
authors.initials: S
authors.lastname: Imada
authors.affiliation: Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan.|Laboratory of Ocean-Earth Life Evolution Research, Japan Agency for Marine-Earth Science and Technology, Kanagawa 237-0061, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Hirose
authors.affiliation: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan.|School of GeoSciences and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3FE, UK.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Komabayashi
authors.affiliation: Laboratory of Ocean-Earth Life Evolution Research, Japan Agency for Marine-Earth Science and Technology, Kanagawa 237-0061, Japan.|Institute for Study of the Earth's Interior, Okayama University, Tottori 682-0193, Japan.
authors.forename: Haruka
authors.initials: H
authors.lastname: Ozawa
authors.affiliation: Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan.|Institute for Study of the Earth's Interior, Okayama University, Tottori 682-0193, Japan.
authors.forename: Shigehiko
authors.initials: S
authors.lastname: Tateno
authors.affiliation: Research and Utilization Division, SPring-8, Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tsutsui
authors.affiliation: Geodynamics Research Center, Ehime University, Ehime 790-8577, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kuwayama
authors.affiliation: Materials Dynamics Laboratory, RIKEN SPring-8 Center, RIKEN, Hyogo 679-5148, Japan.|Research and Utilization Division, SPring-8, Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan.
authors.forename: Alfred Q R
authors.initials: AQ
authors.lastname: Baron