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Recent slowing of Atlantic overturning circulation as a recovery from earlier strengthening

Nature Geoscience volume 9, pages 518–522 (2016)Cite this article

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Abstract

The Atlantic meridional overturning circulation (AMOC) has weakened substantially over the past decade1. Some weakening may already have occurred over the past century2, and global climate models project further weakening in response to anthropogenic climate change3. Such a weakening could have significant impacts on the surface climate4. However, ocean model simulations based on historical conditions have often found an increase in overturning up to the mid-1990s, followed by a decrease5. It is therefore not clear whether the observed weakening over the past decade is part of decadal variability or a persistent weakening6. Here we examine a state-of-the-art global-ocean reanalysis product, GloSea5, which covers the years 1989 to 2015 and closely matches observations of the AMOC at 26.5° N, capturing the interannual variability and decadal trend with unprecedented accuracy. The reanalysis data place the ten years of observations—April 2004 to February 2014—into a longer-term context and suggest that the observed decrease in the overturning circulation is consistent with a recovery following a previous increase. We find that density anomalies that propagate southwards from the Labrador Sea are the most likely cause of these variations. We conclude that decadal variability probably played a key role in the decline of the AMOC observed over the past decade.

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Figure 1: Time series of AMOC strength.
Figure 2: Profiles in the central Labrador Sea.
Figure 3: Propagation of density anomalies in the GloSea5 reanalysis.
Figure 4: Density anomalies at 1,795 m.

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Acknowledgements

This work was supported by the Joint UK DECC/Defra Met Office Hadley Centre Climate Programme (GA01101), the Public Weather Service Research programme, and the EU SPECS project (GA308378). The authors also wish to thank the Met Office Ocean Forecasting, Research and Development team for providing the FOAMv13 system, and B. Blanke and N. Grima for developing and supporting the use of Ariane.

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Authors and Affiliations

  1. Met Office, Fitzroy Road, Exeter EX1 3PB, UK

    Laura C. Jackson, K. Andrew Peterson, Chris D. Roberts & Richard A. Wood

Authors
  1. Laura C. Jackson
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  2. K. Andrew Peterson
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  4. Richard A. Wood
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Contributions

L.C.J. led the writing of the paper, K.A.P. developed and performed the GloSea5 reanalysis, and L.C.J. and C.D.R. performed the analysis. All authors, including R.A.W., contributed to writing and editing the paper.

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Correspondence to Laura C. Jackson.

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The authors declare no competing financial interests.

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Jackson, L., Peterson, K., Roberts, C. et al. Recent slowing of Atlantic overturning circulation as a recovery from earlier strengthening. Nature Geosci 9, 518–522 (2016). https://doi.org/10.1038/ngeo2715

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