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Emerging impact of Greenland meltwater on deepwater formation in the North Atlantic Ocean

Abstract

The Greenland ice sheet has experienced increasing mass loss since the 1990s1,2. The enhanced freshwater flux due to both surface melt and outlet glacier discharge is assuming an increasingly important role in the changing freshwater budget of the subarctic Atlantic3. The sustained and increasing freshwater fluxes from Greenland to the surface ocean could lead to a suppression of deep winter convection in the Labrador Sea, with potential ramifications for the strength of the Atlantic meridional overturning circulation4,5,6. Here we assess the impact of the increases in the freshwater fluxes, reconstructed with full spatial resolution3, using a global ocean circulation model with a grid spacing fine enough to capture the small-scale, eddying transport processes in the subpolar North Atlantic. Our simulations suggest that the invasion of meltwater from the West Greenland shelf has initiated a gradual freshening trend at the surface of the Labrador Sea. Although the freshening is still smaller than the variability associated with the episodic ‘great salinity anomalies’, the accumulation of meltwater may become large enough to progressively dampen the deep winter convection in the coming years. We conclude that the freshwater anomaly has not yet had a significant impact on the Atlantic meridional overturning circulation.

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Figure 1: Circulation and freshwater content of the subpolar North Atlantic.
Figure 2: Fate of the additional Greenland runoff.
Figure 3: Trends in Labrador Sea surface salinity and convection intensity.

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Acknowledgements

The model computations were performed at the North-German Supercomputing Alliance (HLRN). The study was supported by the cooperative programme ‘RACE—Regional Atlantic Circulation and Global Change’ (BMBF grant 03F0651B), and the Cluster of Excellence ‘The Future Ocean’ funded by the DFG. The authors wish to thank the DRAKKAR group for their continuous support in the model development.

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All authors conceived the experiments. E.B. implemented the model and performed the experiments. E.B., C.W.B., K.G. and A.B. analysed the results. C.W.B. wrote the paper with contributions by all co-authors.

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Correspondence to Claus W. Böning.

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The authors declare no competing financial interests.

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Böning, C., Behrens, E., Biastoch, A. et al. Emerging impact of Greenland meltwater on deepwater formation in the North Atlantic Ocean. Nature Geosci 9, 523–527 (2016). https://doi.org/10.1038/ngeo2740

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