1. Decadal fingerprints of fresh water discharge around Greenland in a multi-models ensemble Swingedouw D., Rodehacke C., Behrens E., Menary M., Olsen S., Gao Y., Mikolajewicz U., Mignot J., Biastoch A.

2. Background Greenland ice sheet (GIS) is melting at an increasing rate (Rignot et al. 2011) Potential impact of GIS melting in the future on the Atlantic Meridional Overturning Circulation(AMOC)?

3. Background Stouffer et al. (2006): Spread of AMOC response to fresh water (FW) input?

4. Background Stouffer et al. (2006): Spread of AMOC response to fresh water (FW) input? Regions with a warming in the North Atlantic: an artefact of FW location (50-70°N)?

5. Questions What are the impact and main fingerprints of a more realistic FW discharge mimicking GIS melting? Why does the AMOC respond so differently among AOGCMs? Can warming occur in response to GIS melting? Are atmospheric feedbacks playing an important role?

6. Experimental design 0.1 Sv released around Greenland for the period 1965- 2004 (ocean-only model) ModelTypeOceanAtmosphere HadCM3AOGCMNoName 1.25°– L20 HadAM3 2.5° x 3.75° – L19 IPSLCM5-LRAOGCMNEMO_v3 2° – L31 LMD5 1.8° x 3.75° – L39 COSMOSESMMPI-OM 1.5° – L40 ECHAM6 T63 – L47 EcEarthAOGCMNEMO_v3 1° – L42 IFS T159 – L67 BCM2AOGCMMICOM 2.8° – L35 ARPEGE T63 – L31 ORCA05-KielOGCMNEMO_v3 0.5° – L46 X

7. SSS spread Negative anomaly in the subtropical gyre (fresh water leakage) Positive anomaly in the Arctic

8. SST signature General cooling in the North Atlantic Warming in the Nordic Seas! (except in BCM2)

9. Vertical temperature response Cooling in surface, warming in subsurface in the North Atlantic Emergence of this warm anomaly in the Nordic Seas (except in BCM2)

10. Summary scheme for SSS and SST response Nordic SeasSubpolar Arctic Subtropical

11. Summary scheme for SSS and SST response Nordic SeasSubpolar Arctic Subtropical

12. Ocean circulation response Weakening of barotropic and meridonal overturning circulation in the North Atlantic in most models

13. Barotropic response No clear change in the shape of the gyres Very different shape for the asymmetry between the gyres in the control simulations Rypina et al. 2011

14. Explanation for the AMOC spread AMOC weakening depends on the fresh water leakage intensity a) AMOC vs FW leakage

15. AMOC weakening depends on the fresh water leakage intensity This intensity depends on the gyre asymmetry in control simulations (influencing the FW anomalies escape towards the subtropical gyre) Explanation for the AMOC spread b) AMOC vs gyres asymmetry a) AMOC vs FW leakage

16. Summary scheme for AMOC response Subpolar Nordic Seas Subtropical

17. Summary scheme for AMOC response Subpolar Nordic Seas Subtropical

18. Summary scheme for AMOC response Subpolar Nordic Seas Subtropical

19. Summary scheme for AMOC response Subpolar Nordic Seas Subtropical

20. Summary scheme for AMOC response Subpolar Nordic Seas Subtropical

21. Gyres asymmetry and FW leakage Rypina et al. 2011

22. Climatic fingerprints Large uncertainty over Scandinavia for surface temperature

23. Climatic fingerprints Large uncertainty over Scandinavia for surface temperature Slight southward ITCZ shift

24. Sea level fingerprint Isostatic + dynamic sea level rise (no changes in gravity accounted for) Similar « comma » shape cm

25. Conclusions Quite robust fingerprints of freshwater input FW leakage Arctic salinification Nordic Seas warming OGCM response similar to AOGCM: weak atmospheric feedback AMOC weakening depends on the FW leakage intensity related to the gyres asymmetry

26. Discussion Previous studies may have understimated the impact of GIS melting (Ridley et al. 2005, Jungclaus et al. 2007, Mikolajewicz et al. 2007, Swingedouw et al. 2006) With the observed asymmetry (if the linear relationship holds) : at least 5 Sv (≈20-30%) of weakening for 40 years of 0.1 Sv FW release (≈4% of GIS volume, ≈30cm of SLR )

27. Thank you Didier.Swingedouw@lsce.ipsl.fr