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Decadal fingerprints of fresh water discharge around Greenland in a multi-models ensemble

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. Background.

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Decadal fingerprints of fresh water discharge around Greenland in a multi-models ensemble

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  1. Decadal fingerprints of fresh water discharge around Greenland in a multi-models ensemble Swingedouw D., Rodehacke C., Behrens E., MenaryM., OlsenS., Gao Y., MikolajewiczU., Mignot J., Biastoch A.

  2. Background • Greenlandicesheet (GIS) ismeltingat 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? • Regionswith 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 dischargemimicking GIS melting? • Whydoes the AMOC respondsodifferentlyamongAOGCMs? • Can warmingoccur in response to GIS melting? • Are atmospheric feedbacks playing an important role?

  6. Experimental design 0.1 Sv releasedaroundGreenland for the period 1965-2004 (ocean-only model)

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

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

  9. Vertical temperatureresponse • Cooling in surface, warming in subsurface in the North Atlantic • Emergence of this warm anomaly in the NordicSeas (except in BCM2)

  10. Summaryscheme for SSS and SST response Subpolar NordicSeas Arctic Subtropical

  11. Summaryscheme for SSS and SST response Subpolar NordicSeas Arctic Subtropical

  12. Ocean circulation response Weakening of barotropic and meridonaloverturning circulation in the North Atlantic in mostmodels

  13. Barotropicresponse • No clear change in the shape of the gyres • Verydifferentshape for the asymmetrybetween the gyres in the control simulations Rypina et al. 2011

  14. Explanation for the AMOC spread a) AMOC vs FW leakage • AMOC weakeningdepends on the fresh water leakageintensity

  15. Explanation for the AMOC spread a) AMOC vs FW leakage • AMOC weakeningdepends on the fresh water leakageintensity • This intensitydepends on the gyreasymmetry in control simulations (influencing the FW anomalies escape towards the subtropical gyre) b) AMOC vs gyresasymmetry

  16. Summaryschemefor AMOC response Subpolar NordicSeas Subtropical

  17. Summaryschemefor AMOC response Subpolar NordicSeas Subtropical

  18. Summaryschemefor AMOC response Subpolar NordicSeas Subtropical

  19. Summaryschemefor AMOC response Subpolar NordicSeas Subtropical

  20. Summaryschemefor AMOC response Subpolar NordicSeas Subtropical

  21. Gyresasymmetry and FW leakage Rypina et al. 2011

  22. Climaticfingerprints • Large uncertainty over Scandinavia for surface temperature

  23. Climaticfingerprints • Large uncertainty over Scandinavia for surface temperature • Slightsouthward ITCZ shift

  24. Sealevelfingerprint • Isostatic + dynamicsealevelrise (no changes in gravityaccounted for) • Similar « comma » shape cm

  25. Conclusions • Quiterobustfingerprints of freshwater input • FW leakage • Arcticsalinification • NordicSeaswarming • OGCM responsesimilar to AOGCM: weakatmosphericfeedback • AMOC weakeningdepends on the FW leakageintensityrelated to the gyresasymmetry

  26. Discussion • Previousstudiesmay 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 observedasymmetry(if the linearrelationshipholds): 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

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