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Carbon-depleted outer core revealed by sound velocity measurements of liquid iron–carbon alloy

Author

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  • Yoichi Nakajima

    (Materials Dynamics Laboratory, RIKEN SPring-8 Center, RIKEN)

  • Saori Imada

    (Tokyo Institute of Technology
    Earth-Life Science Institute, Tokyo Institute of Technology)

  • Kei Hirose

    (Earth-Life Science Institute, Tokyo Institute of Technology
    Laboratory of Ocean-Earth Life Evolution Research, Japan Agency for Marine-Earth Science and Technology)

  • Tetsuya Komabayashi

    (Tokyo Institute of Technology
    School of GeoSciences and Centre for Science at Extreme Conditions, University of Edinburgh)

  • Haruka Ozawa

    (Laboratory of Ocean-Earth Life Evolution Research, Japan Agency for Marine-Earth Science and Technology
    Institute for Study of the Earth’s Interior, Okayama University)

  • Shigehiko Tateno

    (Earth-Life Science Institute, Tokyo Institute of Technology
    Institute for Study of the Earth’s Interior, Okayama University)

  • Satoshi Tsutsui

    (SPring-8, Japan Synchrotron Radiation Research Institute)

  • Yasuhiro Kuwayama

    (Geodynamics Research Center, Ehime University)

  • Alfred Q. R. Baron

    (Materials Dynamics Laboratory, RIKEN SPring-8 Center, RIKEN
    SPring-8, Japan Synchrotron Radiation Research Institute)

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.

Suggested Citation

  • Yoichi Nakajima & Saori Imada & Kei Hirose & Tetsuya Komabayashi & Haruka Ozawa & Shigehiko Tateno & Satoshi Tsutsui & Yasuhiro Kuwayama & Alfred Q. R. Baron, 2015. "Carbon-depleted outer core revealed by sound velocity measurements of liquid iron–carbon alloy," Nature Communications, Nature, vol. 6(1), pages 1-7, December.
    • Handle: RePEc:nat:natcom:v:6:y:2015:i:1:d:10.1038_ncomms9942
    DOI: 10.1038/ncomms9942
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