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Decreasing intensity of open-ocean convection in the Greenland and Iceland seas


The air–sea transfer of heat and fresh water plays a critical role in the global climate system1. This is particularly true for the Greenland and Iceland seas, where these fluxes drive ocean convection that contributes to Denmark Strait overflow water, the densest component of the lower limb of the Atlantic Meridional Overturning Circulation (AMOC; ref. 2). Here we show that the wintertime retreat of sea ice in the region, combined with different rates of warming for the atmosphere and sea surface of the Greenland and Iceland seas, has resulted in statistically significant reductions of approximately 20% in the magnitude of the winter air–sea heat fluxes since 1979. We also show that modes of climate variability other than the North Atlantic Oscillation (NAO; refs 3, 4, 5, 6, 7) are required to fully characterize the regional air–sea interaction. Mixed-layer model simulations imply that further decreases in atmospheric forcing will exceed a threshold for the Greenland Sea whereby convection will become depth limited, reducing the ventilation of mid-depth waters in the Nordic seas. In the Iceland Sea, further reductions have the potential to decrease the supply of the densest overflow waters to the AMOC (ref. 8).

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Figure 1: Winter sea-ice extent for the Nordic seas.
Figure 2: Time series of the winter-mean conditions over the Iceland and Greenland sea gyres.
Figure 3: Potential density profiles for October and November used as initial conditions for the PWP model.
Figure 4: Relationship between end-of-winter simulated mixed-layer depths from the PWP model and the atmospheric forcing as represented by the winter-mean open-ocean turbulent heat flux.

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The authors would like to thank the European Centre for Medium-Range Weather Forecasts for access to the ERA-40 and ERA-I reanalyses. G.W.K.M. was supported by the Natural Sciences and Engineering Research Council of Canada. K.V. has received funding from NACLIM, a project of the European Union 7th Framework Programme (FP7 2007–2013) under grant agreement no. 308299, and from the Research Council of Norway under grant agreement no. 231647. R.S.P. was supported by the US National Science Foundation. I.A.R. has received funding from the Natural Environmental Research Council for the ACCACIA project (NE/I028297/1).

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G.W.K.M., K.V., R.S.P. and I.A.R. jointly conceived the study. G.W.K.M. analysed the atmospheric reanalyses and sea-ice data sets. K.V. carried out the ocean mixed-layer modelling. All authors jointly interpreted the results and wrote the manuscript.

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Correspondence to G. W. K. Moore.

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Moore, G., Våge, K., Pickart, R. et al. Decreasing intensity of open-ocean convection in the Greenland and Iceland seas. Nature Clim Change 5, 877–882 (2015).

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