Gulf Stream Variability in Five Oceanic General Circulation Models

Coëtlogon, Gaëlle de; Frankignoul, Claude; Bentsen, Mats; Delon, Claire; Haak, Helmuth; Masina, Simona; Pardaens, A. K.

doi:10.1175/jpo2963.1

Cited by 60 publications

(60 citation statements)

References 45 publications

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“…They are moreover closely linked with the simulated variability of the AMOC strength. Although a similar connection has been observed for shorter simulations (about 50 years; De Coëtlogon et al 2006), it is the first time this is illustrated at longer time scales, and, in particular, in a lastmillennium transient simulation. This result supports inferences of the AMOC variability through reconstructions of the FC intensity with paleo-estimations of the density field.…”

Section: Resultssupporting

confidence: 77%

“…If at all, this would be an argument to render unreliable the reconstructed variability. Earlier modeling studies on the variability of the FC and the AMOC with higher resolution models, albeit for different climate scenarios, supported the idea of covariability between the FC and the AMOC (e.g., Johns et al 2002;De Coëtlogon et al 2006;Lynch-Stieglitz et al 2014).…”

Section: Resultsmentioning

confidence: 88%

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Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

et al. 2016

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the simulated variability at deep/shallow levels. Density changes responsible for the pseudo-reconstructed FCT are mainly driven by zonal temperature differences; salinity differences oppose but play a minor role. These results thus support the use of the thermal-wind relationship to reconstruct the oceanic circulation past variability, in particular at multidecadal timescales. Yet model-data comparison highlights important differences between the simulated and the proxy-based FCT variability. ECHO-G simulates a prominent weakening in the North Atlantic circulation that contrasts with the reconstructed enhancement. Our model results thus do not support the reconstructed FC minimum during the Little Ice Age. This points to a failure in the reconstruction, misrepresented processes in the model, or an important role of internal ocean dynamics.

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Section: Resultssupporting

confidence: 77%

Section: Resultsmentioning

confidence: 88%

Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

et al. 2016

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“…Häkkinen andRhines (2004, 2009) found that the subpolar gyre has slowed down during the 1990s when deep water formation declined. As discussed in Kwon et al (2010), the weakening of the subpolar gyre was reproduced in an eddy-permitting hindcast, and it was highly correlated with a weakening of the AMOC and a northward shift of the Gulf Stream, consistent with earlier simulations (de Coëtlogon et al 2006). On the other hand, Zhang (2008) suggested, based on the GFDL CM2.1 control integration, that the observed decrease in subpolar gyre intensity was correlated with a strengthening of the AMOC and a southward shift of the Gulf Stream due to the increased deep western boundary current (see Zhang and Vallis 2006).…”

supporting

confidence: 84%

Stochastically-driven multidecadal variability of the Atlantic meridional overturning circulation in CCSM3

Kwon

Frankignoul

2011

Clim Dyn

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The Atlantic meridional overturning circulation (AMOC) in the last 250 years of the 700-yearlong present-day control integration of the Community Climate System Model version 3 with T85 atmospheric resolution exhibits a red noise-like irregular multi-decadal variability with a persistence longer than 10 years, which markedly contrasts with the preceding ~300 years of very regular and stronger AMOC variability with ~20 year periodicity. The red noise-like multidecadal AMOC variability is primarily forced by the surface fluxes associated with stochastic changes in the North Atlantic Oscillation (NAO) that intensify and shift northward the deep convection in the Labrador Sea. However, the persistence of the AMOC and the associated oceanic anomalies that are directly forced by the NAO forcing does not exceed about 5 years.The additional persistence originates from anomalous horizontal advection and vertical mixing, which generate density anomalies on the continental shelf along the eastern boundary of the subpolar gyre. These anomalies are subsequently advected by the mean boundary current into the northern part of the Labrador Sea convection region, reinforcing the density changes directly forced by the NAO. As no evidence was found of a clear two-way coupling with the atmosphere, the multi-decadal AMOC variability in the last 250 years of the integration is an ocean-only response to stochastic NAO forcing with a delayed positive feedback caused by the changes in the horizontal ocean circulation.

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“…The other hindcasts similarly show that the intensification of the MOC occurs broadly in phase with that of the subpolar gyre (e.g., Eden and Willebrand 2001, de Coëtlogon et al 2006. Hence, the present simulation seems broadly representative of OGCM simulations, and a key to the differences with the coupled models is the different lead-lag relation between gyre strength and MOC.…”

Section: Summary and Discussionmentioning

confidence: 55%

The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation

2009

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An OGCM hindcast is used to investigate the linkages between North Atlantic Ocean salinity and circulation changes during . The focus is on the eastern subpolar region consisting of the Irminger Sea and the eastern North Atlantic where a careful assessment shows that the simulated interannual to decadal salinity changes in the upper 1500 m reproduce well those derived from the available record of hydrographic measurements. In the model, the variability of the Atlantic meridional overturning circulation (MOC) is primarily driven by changes in deep water formation taking place in the Irminger Sea and, to a lesser extent, the Labrador Sea. Both are strongly influenced by the North Atlantic Oscillation (NAO). The modeled interannual to decadal salinity changes in the subpolar basins are mostly controlled by circulation-driven anomalies of freshwater flux convergence, although surface salinity restoring to climatology and other boundary fluxes each account for approximately 25% of the variance. The NAO plays an important role: a positive NAO phase is associated with increased precipitation, reduced northward salt transport by the wind-driven intergyre gyre, and increased southward flows of freshwater across the Greenland-Scotland ridge. Since the NAO largely controlled deep convection in the subpolar gyre, fresher waters are found near the sinking region during convective events. This markedly differs from the active influence on the MOC that salinity exerts at decadal and longer timescales in most coupled models. The intensification of the MOC that follows a positive NAO phase by about 2 years does not lead to an increase in the northward salt transport into the subpolar domain at low frequencies because it is cancelled by the concomitant intensification of the subpolar gyre which shifts the subpolar front eastward and reduces the northward salt transport by the North Atlantic Current waters. This differs again from most coupled models, where the gyre intensification precedes that of the MOC by several years.3

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Gulf Stream Variability in Five Oceanic General Circulation Models

Cited by 60 publications

References 45 publications

Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

Stochastically-driven multidecadal variability of the Atlantic meridional overturning circulation in CCSM3

The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation

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