Climate Dynamics

, Volume 33, Issue 6, pp 777–793 | Cite as

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

  • Claude FrankignoulEmail author
  • Julie Deshayes
  • Ruth Curry


An OGCM hindcast is used to investigate the linkages between North Atlantic Ocean salinity and circulation changes during 1963–2003. 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 1,500 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.


North Atlantic Oscillation Deep Convection Freshwater Flux Subpolar Gyre Salinity Anomaly 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We thank Helge Drange and Anne Britt Sandø for providing the OGCM data, and the reviewers for their pertinent and constructive comments. Support from NSF Grant 82677800 with the Woods Hole Oceanographic Institution, and (to CF) from the Institut universitaire de France and European FP6 project DYNAMITE (contract 003903-GOCE) and (to JD) from the NOAA Office of Hydrologic Development through a scientific appointment administered by UCAR is gratefully acknowledged.


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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Claude Frankignoul
    • 1
    Email author
  • Julie Deshayes
    • 2
  • Ruth Curry
    • 2
  1. 1.LOCEAN/IPSLUniversité Pierre et Marie Curie, Paris 6Paris Cedex 05France
  2. 2.Woods Hole Oceanographic InstitutionWoods HoleUSA

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