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

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)?

Background

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

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)?

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?

Experimental design0.1 Sv released around Greenland for the period 1965-2004 (ocean-only model)Model Type Ocean AtmosphereHadCM3 AOGCM NoName

1.25°– L20HadAM3 2.5° x 3.75° – L19

IPSLCM5-LR AOGCM NEMO_v3 2° – L31

LMD5 1.8° x 3.75° – L39

COSMOS ESM MPI-OM 1.5° – L40

ECHAM6T63 – L47

EcEarth AOGCM NEMO_v3 1° – L42

IFS T159 – L67

BCM2 AOGCM MICOM2.8° – L35

ARPEGE T63 – L31

ORCA05-Kiel OGCM NEMO_v30.5° – L46

X

SSS spreadNegative anomaly

in the subtropical gyre (fresh water leakage)

Positive anomaly in the Arctic

SST signatureGeneral cooling in

the North Atlantic

Warming in the Nordic Seas! (except in BCM2)

Vertical temperature

responseCooling in surface,

warming in subsurface in the North Atlantic

Emergence of this warm anomaly in the Nordic Seas (except in BCM2)

Summary scheme for SSS and SST response

Nordic SeasSubpolar ArcticSubtropical

Summary scheme for SSS and SST response

Nordic SeasSubpolar ArcticSubtropical

Ocean circulation response

Weakening of barotropic and meridonal overturning circulation in the North Atlantic in most models

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

Explanation for the AMOC spread

AMOC weakening depends on the fresh water leakage intensity

a) AMOC vs FW leakage

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

Summary scheme for AMOC response

Subpolar Nordic SeasSubtropical

Summary scheme for AMOC response

Subpolar Nordic SeasSubtropical

Summary scheme for AMOC response

Subpolar Nordic SeasSubtropical

Summary scheme for AMOC response

Subpolar Nordic SeasSubtropical

Summary scheme for AMOC response

Subpolar Nordic SeasSubtropical

Gyres asymmetry and FW leakage

Rypina et al. 2011

Climatic fingerprints

Large uncertainty over Scandinavia for surface temperature

Climatic fingerprints

Large uncertainty over Scandinavia for surface temperature

Slight southward ITCZ shift

Sea level fingerprint

Isostatic + dynamic sea level rise (no changes in gravity accounted for)

Similar « comma » shape

cm

ConclusionsQuite robust fingerprints of freshwater input

FW leakageArctic salinificationNordic Seas warming

OGCM response similar to AOGCM: weak atmospheric feedback

AMOC weakening depends on the FW leakage intensity related to the gyres asymmetry

DiscussionPrevious 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 )

Thank you

Didier.Swingedouw@lsce.ipsl.fr