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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
Article

Abstract

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.

Keywords

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.

Notes

Acknowledgments

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.

References

  1. Belkin IM, Levitus S, Antonov J, Malmberg SA (2003) Great Salinity Anomalies in the North Atlantic. Prog Oceanogr 41:1–68CrossRefGoogle Scholar
  2. Bentsen M, Drange H (2000) Parameterizing surface fluxes in ocean models using the NCEP/NCAR reanalysis data. In: RegClim General Technical Report 4, Norwegian Institute for Air Research, Kjeller, Norway, 149–158 ppGoogle Scholar
  3. Bentsen M, Drange H, Furevik T, Zhou T (2004) Simulated variability of the Atlantic meridional overturning circulation. Clim Dyn 22:701–720CrossRefGoogle Scholar
  4. Bersch M (2002) North Atlantic Oscillation-induced changes of the upper layer circulation in the northern North Atlantic Ocean. J Geophys Res 107(10):3156. doi: 10.1029/2001JC000901 CrossRefGoogle Scholar
  5. Bleck R, Rooth C, Hu D, Smith LT (1992) Salinity-driven thermocline transients in a wind- and thermohaline-forced isopycnic coordinate model of the North Atlantic. J Phys Oceanogr 22:1486–1505CrossRefGoogle Scholar
  6. Bojariu R, Reverdin G (2002) Large-scale variability modes of freshwater flux and precipitation over the Atlantic. Clim Dyn 18:369–381CrossRefGoogle Scholar
  7. Böning CW, Scheinert M, Dengg J, Biastoch A, Funk A (2006) Decadal variability of subpolar gyre transport and its reverberation in the North Atlantic overturning. Geophys Res Lett 32. doi: 10.1029/2006GL026906
  8. Boyer T, Levitus S, Antonov J, Locarnini R, Mishonov A, Garcia H, Josey SA (2007) Changes in freshwater content in the North Atlantic Ocean. Geophys Res Lett 34. doi: 10.1029/2007GL030126
  9. Bryan F, Danabasglu G, Nakashiki N, Yoshida Y, Kim DH, Tsutsui J (2006) Response of the North Atlantic thermohaline circulation and ventilation to increasing carbon dioxide in CCSM3. J Clim 19:2382–2397CrossRefGoogle Scholar
  10. Cuny J, Rhines PB, Lazier J (2005) Convection above the Labrador continental slope. J Phys Oceanogr 35:489–511CrossRefGoogle Scholar
  11. Curry RG (2002) Hydrobase 2: a database of hydrographic profiles and tools for climatological analysis, Woods Hole Oceanographic Institution. http://www.whoi.edu/science/PO/hydrobase
  12. Curry RG, Mauritzen C (2005) Dilution of the northern North Atlantic ocean in recent decades. Science 308:1772–1774CrossRefGoogle Scholar
  13. Curry RG, McCartney MS (2001) Ocean gyre circulation changes associated with the North Atlantic Oscillation. J Phys Oceanogr 31:3374–3400CrossRefGoogle Scholar
  14. Curry R, Dickson R, Yashayaev I (2003) A change in the freshwater balance of the Atlantic Ocean over the past four decades. Nature 426:826–829CrossRefGoogle Scholar
  15. de Coëtlogon G, Frankignoul C, Bentsen M, Delon C, Haak H, Massina S, Pardaens A (2006) Gulf Stream variability in five oceanic general circulation models. J Phys Oceanogr 36:2119–2135CrossRefGoogle Scholar
  16. Delworth T, Greatbatch RJ (2000) Multidecadal thermohaline circulation variability driven by atmospheric surface flux forcing. J Clim 13:1481–1495CrossRefGoogle Scholar
  17. Delworth T, Manabe S, Stouffer R (1993) Interdecadal variations of the thermohaline circulation in a coupled ocean-atmosphere model. J Clim 6:1993–2011CrossRefGoogle Scholar
  18. Delworth T, Manabe S, Stouffer R (1997) Multidecadal climate variability in the Greenland Sea and surrounding regions: a coupled model simulation. Geophys Res Lett 24:257–260CrossRefGoogle Scholar
  19. Deshayes J, Frankignoul C (2008) Simulated variability of the circulation in the North Atlantic from 1953 to 2003. J Clim 21:4919–4933CrossRefGoogle Scholar
  20. Deshayes J, Frankignoul C, Drange H (2007) Formation and export of deep water in the Labrador and Irminger Seas in a GCM. Deep-Sea Res 54:510–532CrossRefGoogle Scholar
  21. Dickson RR, Brown J (1994) The production of North Atlantic Deep Water, sources, rates, and pathways. J Geophys Res 99:12,319–12,341CrossRefGoogle Scholar
  22. Dickson RR, Meincke J, Malmberg SA, Lee AJ (1988) The “Great Salinity Anomaly” in the northern North Atlantic, 1968–1982. Progr Oceanogr 20:103–151CrossRefGoogle Scholar
  23. Dickson RR, Yashayaev I, Meincke J, Turrel JB, Dye S, Holfort J (2002) Rapid freshening of the deep North Atlantic ocean over the past four decades. Nature 146:832–837CrossRefGoogle Scholar
  24. Dong B, Sutton RT (2005) Mechanisms of interdecadal thermohaline circulation variability in a coupled ocean-atmosphere GCM. J Clim 18:1117–1135CrossRefGoogle Scholar
  25. Drange H, Gerdes R, Gao Y, Karcher F, Bentsen M (2005) Ocean general circulation modelling of the Nordic Seas. In: The Nordic Seas: an integrated perspective. Geophys Monogr, vol 158. American Geophysical Union, Washington DC, pp 199–219Google Scholar
  26. Eden C, Willebrand J (2001) Mechanism of interannual to decadal variability of the North Atlantic Circulation. J Clim 14:2266–2280CrossRefGoogle Scholar
  27. Eden C, Young T (2001) North Atlantic interdecadal variability: oceanic response to the North Atlantic Oscillation (1865–1997). J Clim 14:676–691CrossRefGoogle Scholar
  28. Eldevik T (2002) On frontal dynamics in two model oceans. J Phys Oceanogr 32:2915–2925CrossRefGoogle Scholar
  29. Falina A, Sarafanov A, Sokov A (2007) Variability and renewal of Labrador Sea Water in the Irminger basin in 1991–2004. J Geophys Res 112:C01006. doi: 10.1029/2005JC003348 CrossRefGoogle Scholar
  30. Flatau MK, Talley LD, Niiler PP (2003) The North Atlantic Oscillation, surface current velocities and SST changes in the subpolar North Atlantic. J Phys Oceanogr 19:2355–2369Google Scholar
  31. Ganachaud A, Wunsch C (2000) Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data. Nature 408:453–456CrossRefGoogle Scholar
  32. Haak H, Jungclaus J, Mikolajewicz U, Latif M (2003) Formation and propagation of great salinity anomalies. Geophys Res Lett 30:1473. doi: 10.1029/2003GL017065 CrossRefGoogle Scholar
  33. Häkkinen S (1999) A simulation of thermohaline effects of a great salinity anomaly. J Clim 12:1781–1795CrossRefGoogle Scholar
  34. Häkkinen S (2002) Surface salinity variability in the northern North Atlantic during recent decades. J Geophys Res 107:8003. doi: 10.1029/2001JC000812 CrossRefGoogle Scholar
  35. Häkkinen S, Rhines PB (2004) Decline of subpolar North Atlantic circulation during the 1990s. Science 309:555–559CrossRefGoogle Scholar
  36. Hátún H, Sandø AB, Drange H, Hansen B, Valdimarsson H (2005a) Influence of the Atlantic Subpolar Gyre on the thermohaline circulation. Science 309:1841–1844CrossRefGoogle Scholar
  37. Hátún H, Sandø AB, Drange H, Bentsen M (2005b) Seasonal to decadal temperature variations in the Faroe-Shetland inflow waters. In: Drange H, Dokken TM, Furevik T, Gerdes R, Berger W (eds) The Nordic Seas: an integrated perspective, vol 158. American Geophysical Union, pp 239–250Google Scholar
  38. Hawkins E, Sutton R (2007) Variability of the Atlantic thermohaline circulation described by three-dimensional empirical orthogonal functions. Clim Dyn 29:745–762CrossRefGoogle Scholar
  39. Josey SA, Marsh R (2005) Surface freshwater flux variability and recent freshening of the North Atlantic in the eastern subpolar gyre. J Geophys Res 110:C05008. doi: 10.1029/2004JC002521 CrossRefGoogle Scholar
  40. Jungclaus J, Haak H, Latif M, Mikolajewicz U (2005) Arctic-North Atlantic interactions and multidecadal variability of the meridional overturning circulation. J Clim 18:4013–4031CrossRefGoogle Scholar
  41. Kalnay E et al (1996) The NCEP/NCAR Reanalysis Project. Bull Am Meteor Soc 77:437–471Google Scholar
  42. Kohl A, Stammer D, Cornuelle B (2007) Interannual to decadal changes in the ECCO global synthesis. J Phys Oceanogr 37:313–337CrossRefGoogle Scholar
  43. Latif M, Böning C, Willebrand J, Biastoch A, Dengg J, Keenlyside N, Schweckendiek U (2006) Is the thermohaline circulation changing? J Clim 18:4631–4637CrossRefGoogle Scholar
  44. Lavender KL, Davis RE, Owens WB (2000) Mid-depth recirculation observed in the interior Labrador and Irminger Seas by direct velocity measurements. Nature 407:66–69CrossRefGoogle Scholar
  45. Lazier J, Hendry R, Clarke A, Yashayaev I, Rhines P (2002) Convection and restratification in the Labrador Sea, 1990–2000. Deep Sea Res I 49:1819–1835CrossRefGoogle Scholar
  46. Levitus S, Boyer TP (1994) World Ocean Atlas 1994, vol 4, Temperature. NOAA Atlas NESDIS 4Google Scholar
  47. Levitus S, Burgett R, Boyer TP (1994) World Ocean Atlas 1994, vol 3, Salinity. NOAA Atlas NESDIS 3Google Scholar
  48. Lumpkin R, Speer K (2003) Large-scale vertical and horizontal circulation in the North Atlantic ocean. J Clim 33:1902–1920Google Scholar
  49. Mauritzen C, Hjøllo SS, Sandø AB (2006) Passive tracers and active dynamics: a model study of hydrography and circulation in the northern North Atlantic. J Geophys Res 111:C08014. doi: 10.1029/2005JC003252 CrossRefGoogle Scholar
  50. Mignot J, Frankignoul C (2004) Interannual to interdecadal variability of sea surface salinity in the Atlantic and its link to the atmosphere in a coupled model. J Geophys Res 109:C04005CrossRefGoogle Scholar
  51. Msadek R, Frankignoul C (2008) Atlantic multidecadal oceanic variability and its influence on the atmosphere in a climate model. Clim Dyn. doi: 10.1007/s00382-008-0452-0
  52. Peterson BJ, McClelland J, Curry R, Homes RM, Walsh JE, Agaard K (2006) Trajectory shifts in the Arctic and subarctic freshwater cycle. Science 313:1061–1066CrossRefGoogle Scholar
  53. Pickart RS, Straneo F, Moore GWK (2003) Is Labrador Sea Water formed in the Irminger basin? Deep-Sea Res Part 1 50:23–52CrossRefGoogle Scholar
  54. Reverdin G, Niiler PP, Valdimarsson H (2003) North Atlantic ocean surface currents. J Geophys Res 108. doi: 10.1029/2001JC001020
  55. Rhein M, Fischer J, Smethie WM, Smythe-Wright D, Weiss RF, Mertens C, Min DH, Fleischmann U, Putka A (2002) Labrador Sea Water: pathways, CFC inventory and formation rates. J Phys Oceanogr 32:648–665CrossRefGoogle Scholar
  56. Rousset C, Houssais MN, Chassignet E (2007) A multi-model study of the restratification phase in an idealized convection basin. Ocean Dyn (submitted)Google Scholar
  57. Schweckendiek U, Willebrand J (2005) Mechanisms affecting the overturning response in global warming simulations. J Clim 18:4925–4936CrossRefGoogle Scholar
  58. Vellinga M, Wood RA (2002) Global climatic impacts of a collapse of the Atlantic thermohaline circulation. Clim Change 54:251–267CrossRefGoogle Scholar
  59. Vellinga M, Wu P (2004) Low-latitude freshwater influence on centennial variability of the Atlantic thermohaline circulation. J Clim 17:4498–4511CrossRefGoogle Scholar
  60. Willebrand J et al (2001) Circulation characteristics in three eddy-permitting models of the North Atlantic. Progr Oceanogr 48:123–161Google Scholar
  61. Wu P, Wood R, Stott P (2004) Does the recent freshening trend in the North Atlantic indicate a weakening of the thermohaline circulation? Geophys Res Lett 31:L02301. doi: 10.1029/2003GL018584 CrossRefGoogle Scholar
  62. Zhu X, Jungclaus J (2008) Interdecadal variability of the meridional overturning circulation as an ocean internal mode. Clim Dyn 31:731–741CrossRefGoogle Scholar

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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