Article | Published:

Tidal tomography constrains Earth’s deep-mantle buoyancy

Nature volume 551, pages 321326 (16 November 2017) | Download Citation

Abstract

Earth’s body tide—also known as the solid Earth tide, the displacement of the solid Earth’s surface caused by gravitational forces from the Moon and the Sun—is sensitive to the density of the two Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific. These massive regions extend approximately 1,000 kilometres upward from the base of the mantle and their buoyancy remains actively debated within the geophysical community. Here we use tidal tomography to constrain Earth’s deep-mantle buoyancy derived from Global Positioning System (GPS)-based measurements of semi-diurnal body tide deformation. Using a probabilistic approach, we show that across the bottom two-thirds of the two LLSVPs the mean density is about 0.5 per cent higher than the average mantle density across this depth range (that is, its mean buoyancy is minus 0.5 per cent), although this anomaly may be concentrated towards the very base of the mantle. We conclude that the buoyancy of these structures is dominated by the enrichment of high-density chemical components, probably related to subducted oceanic plates or primordial material associated with Earth’s formation. Because the dynamics of the mantle is driven by density variations, our result has important dynamical implications for the stability of the LLSVPs and the long-term evolution of the Earth system.

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Acknowledgements

H.C.P.L. and J.X.M. acknowledge support from NSF CSEDI grant EAR-1464024, NASA grant NNX17AE42G, and Harvard University. J.L.D. was supported in part by NASA grant NNX17AD97G. H.-Y.Y. was supported by the Chinese Academy of Sciences under grant number XDB18010304 and 2015TW1ZB0001. H.C.P.L. thanks J. Austermann for performing mantle convection simulations during the review process.

Author information

Affiliations

  1. Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA

    • Harriet C. P. Lau
    •  & Jerry X. Mitrovica
  2. Lamont-Doherty Earth Observatory, Columbia University, New York, USA

    • James L. Davis
  3. Department of Geosciences and Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey, USA

    • Jeroen Tromp
  4. Laboratory of Seismology and Physics of Earth’s Interior & School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China

    • Hsin-Ying Yang
  5. National Geophysical Observatory at Mengcheng, University of Science and Technology of China, Anhui, China

    • Hsin-Ying Yang
  6. Department of Earth Sciences, University of Cambridge, Cambridge, UK

    • David Al-Attar

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Contributions

H.C.P.L. led the development of the body tide theory, the numerical/statistical analysis of GPS measurements of semi-diurnal body tides reported in the literature, and the writing of the manuscript. J.X.M. contributed to the statistical analysis and interpretation of the results while J.L.D. contributed algorithms to calculate tidal amplitudes and investigated potential impacts of GPS orbit errors. J.T., D.A.-A., H.-Y.Y. and J.X.M. contributed to the development of the body tide theory and numerical software. All these authors contributed text to the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Harriet C. P. Lau.

Reviewer Information Nature thanks L. Métivier, B. Romanowicz and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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https://doi.org/10.1038/nature24452

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