Latitudinal shift of the Atlantic Meridional Overturning Circulation source regions under a warming climate

Abstract

The strength of the Atlantic Meridional Overturning Circulation, a key indicator of the climate state, is maintained by the subduction of dense water that feeds the deep southwards branch. At present, this subduction occurs almost entirely in the subpolar region, in the Labrador, Irminger and Nordic seas; however, whether this will continue under climate change is unknown. Here we use a quantitative Lagrangian diagnostic applied to climate model output to show that, in response to warming, the main source regions of this mixed-layer subduction shift northwards to the Arctic Basin and southwards to the subtropical gyre. These shifts are explained by changes in background stratification, mixed-layer depth and ocean circulation, highlighting the need to consider the full three-dimensionality of the circulation and its changes to accurately predict the future climate state.

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Fig. 1: AMOC strength at 26° N in CTRL and 4 × CO2.
Fig. 2: Regional contributions to the AMOC streamfunctions at 26° N.
Fig. 3: Changes in MLD and subduction rates.
Fig. 4: Changes in stratification and gyre circulation.
Fig. 5: Changes in the dominant source regions of the AMOC deep limb.

Data availability

The data sets generated and analysed during the current study are available upon request from the corresponding author.

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Acknowledgements

We are deeply grateful to A. Voldoire and R. Séférian (CNRM, Toulouse, France) for making the model outputs from the different simulations available, and providing guidance on their use.

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C.L. and M.T. designed the study. M.T. performed the Lagrangian analysis. C.L. and M.T. analysed the results. C.L. wrote the manuscript with input from M.T.

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Correspondence to Camille Lique.

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Lique, C., Thomas, M.D. Latitudinal shift of the Atlantic Meridional Overturning Circulation source regions under a warming climate. Nature Clim Change 8, 1013–1020 (2018). https://doi.org/10.1038/s41558-018-0316-5

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