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Enhanced weathering and CO2 drawdown caused by latest Eocene strengthening of the Atlantic meridional overturning circulation

Nature Geoscience volume 10, pages 213216 (2017) | Download Citation

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Abstract

On timescales significantly greater than 105 years, atmospheric pCO2 is controlled by the rate of mantle outgassing relative to the set-point of the silicate weathering feedback. The weathering set-point has been shown to depend on the distribution and characteristics of rocks exposed at the Earth’s surface, vegetation types and topography. Here we argue that large-scale climate impacts caused by changes in ocean circulation can also modify the weathering set-point and show evidence suggesting that this played a role in the establishment of the Antarctic ice sheet at the Eocene–Oligocene boundary. In our simulations, tectonic deepening of the Drake Passage causes freshening and stratification of the Southern Ocean, strengthening the Atlantic meridional overturning circulation and consequently raising temperatures and intensifying rainfall over land. These simulated changes are consistent with late Eocene tectonic reconstructions that show Drake Passage deepening, and with sediment records that reveal Southern Ocean stratification, the emergence of North Atlantic Deep Water, and a hemispherically asymmetric temperature change. These factors would have driven intensified silicate weathering and can thereby explain the drawdown of carbon dioxide that has been linked with Antarctic ice sheet growth. We suggest that this mechanism illustrates another way in which ocean–atmosphere climate dynamics can introduce nonlinear threshold behaviour through interaction with the geologic carbon cycle.

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Change history

  • 15 February 2017

    In the version of this Article originally published, a sentence was mistakenly omitted from the Acknowledgements: "We thank John Higgins for insightful discussions, and for inspiring us to consider the role of silicate weathering." This has been corrected in all versions of the Article.

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Acknowledgements

We thank J. Higgins for insightful discussions, and for inspiring us to consider the role of silicate weathering. Computational resources were provided by the Canadian Foundation for Innovation (CFI) and Compute Canada, through a resource allocation to E.G. Simulations were integrated on the Scinet general purpose cluster at the University of Toronto. The Canadian Institute for Advanced Research (CIFAR) and the Spanish Ministry of Economy and Competitiveness, through the María de Maeztu Programme for Units of Excellence in R&D (MDM-2015-0552), supported involvement of E.G. and an NSERC Discovery grant supported involvement of G.H.

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Affiliations

  1. Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 0E8, Canada

    • Geneviève Elsworth
    • , Eric Galbraith
    •  & Galen Halverson
  2. Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain

    • Eric Galbraith
  3. Institut de Ciencia i Technologia Ambientals (ICTA) and Department of Mathematics, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain

    • Eric Galbraith
  4. Department of Environmental Systems Science, ETH Zürich, Universitätsstrasse 16, Zürich 8092, Switzerland

    • Simon Yang

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Contributions

G.E. compiled geochemical data and prepared the manuscript. E.G. prepared the manuscript, performed model simulations and analysed simulation results. G.H. prepared the manuscript and assisted in analysis of geochemical data. S.Y. performed the model simulations and analysed simulation results.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Geneviève Elsworth.

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https://doi.org/10.1038/ngeo2888

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