decadal fingerprints of fresh water discharge around greenland in a multi-models ensemble
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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. - PowerPoint PPT PresentationTRANSCRIPT
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 )
