Article

Abyssal ocean overturning shaped by seafloor distribution

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Abstract

The abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less-dense waters above them. Understanding what controls the strength and structure of these interhemispheric flows—referred to as the abyssal overturning circulation—is key to quantifying the ocean’s ability to store carbon and heat on timescales exceeding a century. Here we show that, north of 32° S, the depth distribution of the seafloor compels dense southern-origin waters to flow northward below a depth of about 4 kilometres and to return southward predominantly at depths greater than 2.5 kilometres. Unless ventilated from the north, the overlying mid-depths (1 to 2.5 kilometres deep) host comparatively weak mean meridional flow. Backed by analysis of historical radiocarbon measurements, the findings imply that the geometry of the Pacific, Indian and Atlantic basins places a major external constraint on the overturning structure.

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Acknowledgements

We thank P. Barker and J. Dunn for their help with the mapping and for providing the distance look-up tables. We also thank J. Nycander, A. Melet, M. Nikurashin and J. Goff for sharing their published datasets. C.d.L., R.M.H. and T.J.McD. gratefully acknowledge Australian Research Council support through grant FL150100090.

Author information

Affiliations

  1. School of Mathematics and Statistics, University of New South Wales, Sydney, New South Wales 2052, Australia

    • C. de Lavergne
    • , R. M. Holmes
    •  & T. J. McDougall
  2. LOCEAN Laboratory, Sorbonne Universités (Université Pierre et Marie Curie Paris 6)-CNRS-IRD-MNHN, F-75005 Paris, France

    • C. de Lavergne
    •  & G. Madec
  3. Department of Meteorology (MISU), Stockholm University, 114 18 Stockholm, Sweden

    • F. Roquet
  4. Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, New South Wales 2052, Australia

    • R. M. Holmes

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Contributions

C.d.L. designed and conducted the analysis. G.M., F.R., R.M.H. and T.J.McD. contributed to analysis and presentation choices and to the scientific interpretation of results. C.d.L. prepared the manuscript. G.M., F.R., R.M.H. and T.J.McD. assisted in the writing.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to C. de Lavergne.

Reviewer Information Nature thanks R. Key and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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