Utrecht, 16/02/2012 Quantifying the AMOC feedbacks during a 2xCO2 stabilization experiment with land-ice melting Swingedouw Didier

Utrecht, 16/02/2012 AMOC spread in projections Large spread of AMOC response to GHG emissions Gregory et al. 2005: heat flux and freshwater flux both play a role Need for understanding processes Even for a given forcing: large spread Stouffer et al Schneider et al., 2007

Utrecht, 16/02/2012 Opposing effects for the water coming from the Arctic and the tropics AMOC and salinity forcing Swingedouw et al. 2007a Evaporation Precipitations Runoff Humidity transport Salinity advection

Utrecht, 16/02/2012 Actuel Opposing effects for the water coming from the Arctic and the tropics AMOC and salinity forcing Swingedouw et al. 2007a Evaporation Precipitations Runoff Humidity transport Salinity advection

Utrecht, 16/02/2012 ActuelFutur Opposing effects for the water coming from the Arctic and the tropics AMOC and salinity forcing Swingedouw et al. 2007a Evaporation Precipitations Runoff Humidity transport Salinity advection

Utrecht, 16/02/2012 ActuelFutur Opposing effects for the water coming from the Arctic and the tropics AMOC and salinity forcing Swingedouw et al. 2007a Evaporation Precipitations Runoff Humidity transport Salinity advection

Utrecht, 16/02/2012 ActuelFutur Opposing effects for the water coming from the Arctic and the tropics AMOC and salinity forcing Swingedouw et al. 2007a Evaporation Precipitations Runoff Humidity transport Salinity advection

Utrecht, 16/02/2012 ActuelFutur Opposing effects for the water coming from the Arctic and the tropics AMOC and salinity forcing Swingedouw et al. 2007a Evaporation Precipitations Runoff Humidity transport Salinity advectin

Utrecht, 16/02/2012 ActuelFutur Opposing effects for the water coming from the Arctic and the tropics AMOC and salinity forcing Swingedouw et al. 2007a Evaporation Precipitations Runoff Humidity transport Salinity advectin

Utrecht, 16/02/2012 Effect – Effect + Oceanic meridional advection Temperature density flux Salinity density flux AMOCiFCMs AMOC internal feedbacks Stocker et al., 2001

Utrecht, 16/02/2012 Effect – Effect + Oceanic meridional heat transport Oceanic meridional advection Meridional atmospheric Temperature gradient Sea ice amount Brine rejection Ekman divergence Freshwater meridional transport Sea ice transport and melting Temperature density flux Salinity density flux Salinity density flux THCeTCMOs Stocker et al., 2001 AMOCi AMOC internal feedbacks

Utrecht, 16/02/2012 Questions How to quantify the mechanisms explaining the response of the AMOC to GHG increase? Can an additional freshwater input lead to substantial AMOC weakening in projections? What are the roles of feedbacks and forcing for the response of the AMOC?

Utrecht, 16/02/2012 Experimental design Snow Land Ocean Ice IPSL-CM4 model: OPA-ORCA2 (0.5°-2°) LMDz (2.5° x 3.75°) 2xCO2 scenario lasting for 500 years: With ice sheet melting No ice sheet melting Net heat flux Temps (année s) CO2 (ppm) CTL No With Time (years)) (Swingedouw et al. 2007b)

Utrecht, 16/02/2012 AMOC and convection sites Climatology: Boyer Montegut et al., 2005IPSL-CM4: CTL In CTL simulation: AMOC max. of only 11 Sv (obs. around 18 Sv ) No convection in the Labrador Sea Overflow of 5.6 Sv (obs. around 6 Sv) JFM mixed layer depth

Utrecht, 16/02/2012 Greenland ice sheet (GrIS) melting amounts to 0.13 Sv after 200 years and is then constant Equivalent melting of GrIS by more than 50% after 500 years=very agressive melting scenario With CTL No AMOC index Tem ps (ann ées) CO2 (ppm) CTL No With Time (years) ) Temps (année s) CTL No With Global temperature Model responses

Utrecht, 16/02/2012 AMOC and density in the convection sites Correlation of 0.98 between density in the black box and the AMOC: t=0 No-CTL With-CTL

Name of the meeting, 20/06/2011 Influence of haline and thermal response on the AMOC With melting: Changes in temperature (T) and salinity (S) weakens the density (and AMOC)

Name of the meeting, 20/06/2011 Influence of haline and thermal response on the AMOC With melting: Changes in temperature (T) and salinity (S) weakens the density (and AMOC) No melting: Salinity changes explain the recovery

Utrecht, 16/02/2012 Density budget in the convection box Transport Surface

Utrecht, 16/02/2012 Density buget in the convection box after 500 years AMOC increases AMOC decreases Transport SurfaceResidualBudget No-CTL With-CTL

Utrecht, 16/02/2012 Transport SurfaceRésiduBilan Sans-CTRL Avec-CTRL AMOC increases AMOC decreases Density buget in the convection box after 500 years

Utrecht, 16/02/2012 Synthesis of important factor explaining density budget in No ice sheet melting Over 500 years AMOC reduction mainly caused by: o Warming in the convection sites (26 %) o Salinity transport by the overturning (65 %) AMOC recovery mainly caused by: o Transport of salinity anomalies by the gyre (40 %) o Sea ice melting reduction in the convection sites (28 %)

Utrecht, 16/02/2012 Sea ice melting anomalies CTL: Sea ice transport through Fram Strait Brine rejection in winter when sea ice forms + = No melting projections (after 500 years): Sea ice transport decreases Brine rejection decreases Sv Sea ice transport in CTL CTL No

Utrecht, 16/02/2012 Salinity anomalies in the Atlantic SSS anomalies: No melting - CTL

Utrecht, 16/02/2012 Feedback amplification Linear feedback model (Hansen et al., 1984, for climate sensitivity): G 0 : Static gain λ i : Feedback factors + -

Utrecht, 16/02/2012 Feedback quantification methology now stands for the difference between the projections We isolate GrIS melting effect: wit h

Utrecht, 16/02/2012 Quantification of feedback factors Dynamical gain: Climatic system transfer Temperature Density flux Salinity Density flux AMOC_in AMOC_out + - +

Utrecht, 16/02/2012 TransportSurface Résidu Salinity Temperature TransportSurface Résidu Heat flux feedback strongly damps heat transport feedback Ocean transport Temperature density flux Salinity density flux AMOCin AMOCout + - Local atmospheric damping Quantification of feedback factors

Utrecht, 16/02/2012 Quantifying the AMOC feedbacks among different AOGCMs For a given freshwater input, large spread among AOGCMs (Stouffer et al. 2006) Methodology of feedbacks quantification could be useful (Swingedouw et al. 2007) Application to the models from this project framework? Climatic system transfer Temperature Density flux Salinity Density flux AMOC_in AMOC_out Stouffer et al. 2006

Utrecht, 16/02/2012 THOR water hosing 6 models including one OGCM with 0.1 Sv

Utrecht, 16/02/2012 THOR project: Swingedouw et al., in prep. An hypothesis to explain AMOC spread Rypina et al. 2011

Utrecht, 16/02/2012 Outlooks Quantifying AMOC feedbacks in the different EMBRACE models Evaluating impact of gyre asymmetry on gyre feedbacks factor Limits/challenges Computation of density budget in a model Assumption of AMOC related to density in convection zone holds in other models

Utrecht, 16/02/2012 Predefined sections across the North Atlantic 26N RAPID OVIDE A25 AR7W 42N interface between the subtropical and subpolar gyres overflows : connection between the subpolar gyre and the Nordic Seas connection with the Arctic ocean reference salinity : 34.8

Utrecht, 16/02/2012 FCVAR from Julie Deshayes: Diagnostic package of 3D metrics of the circulation model configurations and simulations GFDL CM3 CNRM CM5 IPSL CM5 CCSM4 + HADGEM2 ? + HADGEM3 ? pre-industrial control runs monthly output + ocean-only simulations ORCA2-OON2 ORCA1-OCEP09 ORCA025.L75-G85 GLORYS2V1 load grid points scale factors identify sections and areas as sequences of grid points extract data (t,z,l) along sections and areas load data u, v, θ, S (t,z,y,x) predefined sections and areas defined by (lat,lon) of end points + additional sections calculate indices (t) for sections, ie components of the northward transport of mass, heat and salt: net (with and without net mass flux) overturning in vertical coordinates overturning in density coordinates barotropic baroclinic (net-overturning-barotropic) 0 to1000m deep 1000 to 2000m deep 2000m deep to bottom related to thermal wind (only from ρ) calculate indices (t) for areas, regarding heat and freshwater: volume changes advective fluxes at ocean boundaries eddy fluxes at ocean boundaries diffusion, ice + atmospheric fluxes Matlab package available to the community

Utrecht, 16/02/2012 Thank you

Utrecht, 16/02/2012 Convection sites density as a driver of AMOC? Strong assumption from the proposed model Gregory and Tailleux (2010): buoyancy fluxes over the convection sites as a production of Available potential energy then used for Kinetic energy production

Utrecht, 16/02/2012 Linear feedback factor and hysteresis Stommel et al. (1961): non linearity for the response of the AMOC to freshwater input This would appears in the feedback factor of the overturning terms for salinity and heat transport (dependent in the mean state)

Utrecht, 16/02/2012 Transport Chaleur Méridien Océanique Advection Méridienne Océanique Gradient Température Méridien Atmosphérique Formation Glace Rejet de Sel Glace Divergence Ekman, locale Transport Eau Douce Méridien Transport, Fonte Glace Flux Densité Température Flux Densité Salinité Flux Densité Salinité THCeTCMOs - Réchauffement climatique + + Action - Action + Réchauffement climatique

Utrecht, 16/02/2012 Avec fonte : convection disparaît Sans fonte : renforcement de la convection en mer de GIN, diminution en mer d’Irminger Réponses des sites de convection Avec : année 500 CTL Sans : année 500

Utrecht, 16/02/2012 Représentation de la THC dans le modèle Fonction de courant latitude-profondeur en Atlantique Latitude Profondeur  2 cellules avec NADW et AABW  Maximum pour la NADW d’environ 11 Sv (Indice THC)  Plus faible que les estimations issues d’observations (14-18 Sv) Sv