Climate Dynamics

, Volume 34, Issue 7–8, pp 953–968 | Cite as

Seawater density variations in the North Atlantic and the Atlantic meridional overturning circulation

  • Chunzai WangEmail author
  • Shenfu Dong
  • Ernesto Munoz


Seawater property changes in the North Atlantic Ocean affect the Atlantic meridional overturning circulation (AMOC), which transports warm water northward from the upper ocean and contributes to the temperate climate of Europe, as well as influences climate globally. Previous observational studies have focused on salinity and freshwater variability in the sinking region of the North Atlantic, since it is believed that a freshening North Atlantic basin can slow down or halt the flow of the AMOC. Here we use available data to show the importance of how density patterns over the upper ocean of the North Atlantic affect the strength of the AMOC. For the long-term trend, the upper ocean of the subpolar North Atlantic is becoming cooler and fresher, whereas the subtropical North Atlantic is becoming warmer and saltier. On a multidecadal timescale, the upper ocean of the North Atlantic has generally been warmer and saltier since 1995. The heat and salt content in the subpolar North Atlantic lags that in the subtropical North Atlantic by about 8–9 years, suggesting a lower latitude origin for the temperature and salinity anomalies. Because of the opposite effects of temperature and salinity on density for both long-term trend and multidecadal timescales, these variations do not result in a density reduction in the subpolar North Atlantic for slowing down the AMOC. Indeed, the variations in the meridional density gradient between the subpolar and subtropical North Atlantic Ocean suggest that the AMOC has become stronger over the past five decades. These observed results are supported by and consistent with some oceanic reanalysis products.


Atlantic Meridional Overturn Circulation North Atlantic Ocean Simple Ocean Data Assimilation Potential Density Atlantic Multidecadal Oscillation 
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 reviewers’ suggestions and comments on this manuscript. We also thank Tim Boyer who provided us the updated salinity data before its public release. Gail Derr gave some editorial comments on an early version of the manuscript. This work was supported by a grant from National Oceanic and Atmospheric Administration (NOAA) Climate Program Office and by the base funding of NOAA Atlantic Oceanographic and Meteorological Laboratory (AOML). The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the funding agency.


  1. Balmaseda MA, Smith GC, Haines K, Anderson D, Palmer TN, Vidard A (2007) Historical reconstruction of the Atlantic meridional overturning circulation from the ECMWF operational ocean reanalysis. Geophys Res Lett 34:L23615. doi: 10.1029/2007GL031645 CrossRefGoogle Scholar
  2. Bell GD, Chelliah M (2006) Leading tropical modes associated with interannual and multidecadal fluctuations in north Atlantic hurricane activity. J Clim 19:590–612CrossRefGoogle Scholar
  3. Boyer TP, Levitus S, Antonov JI, Locarnini RA, Garcia HE (2005) Linear trends in salinity for the World Ocean, 1955–1998. Geophys Res Lett 32:L01604. doi: 10.1029/2004GL021791 CrossRefGoogle Scholar
  4. Boyer TP et al (2006) World ocean database 2005. In: Levitus S et al (eds) NOAA atlas NESDIS, vol 60. US Government Printing Office, Washington DC, 190 ppGoogle Scholar
  5. Boyer TP et al (2007) Changes in freshwater content in the North Atlantic Ocean 1955–2006. Geophys Res Lett 34:L16603. doi: 10.1029/2007GL030126 CrossRefGoogle Scholar
  6. Bryan K, Cox M (1967) A numerical investigation of the oceanic general circulation. Tellus 19:54–80CrossRefGoogle Scholar
  7. Bryden HL, Longworth HL, Cunningham SA (2005) Slowing of the Atlantic meridional overturning circulation at 25°N. Nature 438:655–657CrossRefGoogle Scholar
  8. Carton JA, Giese BS (2008) A reanalysis of ocean climate using Simple Ocean Data Assimilation (SODA). Mon Weather Rev 136:2999–3017CrossRefGoogle Scholar
  9. Conkright ME et al (2002) World Ocean Database 2001. In: Levius S (eds) NOAA Atlas NESDIS 42, vol 1. US Government Printing Office, Washington DC, 167 ppGoogle Scholar
  10. Curry R, Dickson B, Yashayaev I (2003) A change in the freshwater balance of the Atlantic Ocean over the past four decades. Nature 426:826–829CrossRefGoogle Scholar
  11. Delworth TL, Mann ME (2000) Observed and simulated multidecadal variability in the Northern Hemisphere. Clim Dyn 16:661–676CrossRefGoogle Scholar
  12. Dickson B et al (2002) Rapid freshening of the deep North Atlantic Ocean over the past four decades. Nature 416:832–837CrossRefGoogle Scholar
  13. Dijkstra HA, te Raa L, Schmeits M, Gerrits J (2006) On the physics of the Atlantic multidecadal oscillation. Ocean Dyn 56:36–50CrossRefGoogle Scholar
  14. Dong BW, Sutton TT (2002) Adjustment of the coupled ocean–atmosphere system to a sudden change in the thermohaline circulation. Geophys Res Lett 29:1728. doi: 10.1029/2002GL015229 CrossRefGoogle Scholar
  15. Enfield DB, Mestas-Nunez AM, Trimble PJ (2001) The Atlantic Multidecadal Oscillation and its relationship to rainfall and river flows in the continental US. Geophys Res Lett 28:2077–2080CrossRefGoogle Scholar
  16. Gill AE (1982) Atmosphere–ocean dynamics. Academic Press, New York, p 662Google Scholar
  17. Goldenberg SB, Landsea CW, Maestas-Nunez AM, Gray WM (2001) The recent increase in Atlantic hurricane activity: causes and implications. Science 293:474–479CrossRefGoogle Scholar
  18. Gray ST, Graumlich JL, Betancourt JL, Pederson GT (2004) A tree-ring based reconstruction of the Atlantic multidecadal oscillation since 1567 A.D. Geophys Res Lett 31:L12205. doi: 10.1029/2004GL019932 CrossRefGoogle Scholar
  19. Hegerl GC et al (2007) Understanding and attributing climate change. In: Solomon S et al (eds) Climate change 2007: the physical science basis. Contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change. Cambridge University Press, Cambridge and New YorkGoogle Scholar
  20. Hughes T, Weaver A (1994) Multiple equilibrium of an asymmetric two-basin model. J Phys Oceanogr 24:619–637CrossRefGoogle Scholar
  21. Josey SA, Kent EC, Taylor PK (1998) The Southampton Oceanography Centre (SOC) ocean–atmosphere heat, momentum and freshwater flux atlas. Southampton Oceanography Centre Report No. 6, 30 ppGoogle Scholar
  22. Knight JR, Allan RJ, Folland CK, Vellinga M, Mann ME (2005) A signature of persistent natural thermohaline circulation cycles in observed climate. Geophys Res Lett 32:L20708. doi: 10.1029/2005GL024233 CrossRefGoogle Scholar
  23. Kohl A, Dommenget D, Ueyoshi K, Stammer D (2006) The Global ECCO 1952 to 2001 ocean synthesis. ECCO Report No. 40Google Scholar
  24. Krebs U, Timmermann A (2007) Tropical air–sea interactions accelerate the recovery of the Atlantic Meridional Overturning Circulation after a major shutdown. J Clim 20:4940–4956CrossRefGoogle Scholar
  25. Kuhlbrodt T et al (2007) On the driving processes of the Atlantic meridional overturning circulation. Rev Geophys 45:RG2001. doi: 10.1029/2004RG000166 CrossRefGoogle Scholar
  26. Latif M, Roeckner E, Mikolajewicz U, Voss R (2000) Tropical stabilization of the thermohaline circulation in a greenhouse warming simulation. J Clim 13:1809–1813CrossRefGoogle Scholar
  27. Lozier MS, Leadbetter S, Williams RG, Roussenov V, Reed MSC, Moore NJ (2008) The spatial pattern and mechanisms of heat-content change in the North Atlantic. Science 319:800–803CrossRefGoogle Scholar
  28. Manabe S, Stouffer RJ, Spelman MJ, Bryan K (1991) Transient response of a coupled ocean–atmosphere model to gradual changes of atmospheric CO2. Part I: annual mean response. J Clim 4:785–818CrossRefGoogle Scholar
  29. Mann ME, Emanuel KA (2006) Atlantic hurricane trends linked to climate change. Eos Trans AGU 87:233–244. doi: 10.1029/2006EO240001 Google Scholar
  30. McCabe G, Palecki M, Betancourt J (2004) Pacific and Atlantic Ocean influences on multidecadal drought frequency in the United States. Proc Natl Acad Sci 101:4136–4141CrossRefGoogle Scholar
  31. Park YG (1999) The stability of thermohaline circulation in a two-box model. J Phys Oceanogr 29:3101–3110CrossRefGoogle Scholar
  32. Rabe B, Schott FA, Kohl A (2008) Mean circulation and variability of the tropical Atlantic during 1952–2001 in the GECCO assimilation fields. J Phys Oceanogr 38:177–192CrossRefGoogle Scholar
  33. Rosati A, Harrison M, Wittenberg A, Zhang S (2004) NOAA/GFDLocean data assimilation activities. CLIVAR Workshop on Ocean Reanalysis, 9 November 2004. NCAR, BoulderGoogle Scholar
  34. Santer BD et al (2006) Forced and unforced ocean temperature changes in Atlantic and Pacific tropical cyclogenesis regions. Proc Natl Acad Sci 203:13905–13910CrossRefGoogle Scholar
  35. Schmittner A, Chiang JCH, Hemming SR (2007) Ocean circulation: mechanisms and impacts. Geophysical Monograph Series, vol 173. American Geophysical Union, Washington, 392 ppGoogle Scholar
  36. Scott J, Marotzke J, Stone P (1999) Interhemispheric thermohaline circulation in a coupled box model. J Phys Oceanogr 29:351–365CrossRefGoogle Scholar
  37. Stommel H (1961) Thermohaline convection with two stable regimes of flow. Tellus 13:224–230CrossRefGoogle Scholar
  38. Thorpe RB, Gregory JM, Johns TC, Wood RA, Mitchell JFB (2001) Mechanisms determining the Atlantic thermohaline circulation response to greenhouse gas forcing in a non-flux-adjusted coupled climate model. J Clim 14:3102–3116CrossRefGoogle Scholar
  39. Timmermann A et al (2007) The influence of a weakening of the Atlantic meridional overturning circulation on ENSO. J Clim 20:4899–4919CrossRefGoogle Scholar
  40. Vellinga M, Wood RA (2002) Global climatic impacts of a collapse of the Atlantic thermohaline circulation. Clim Changes 54:251–267CrossRefGoogle Scholar
  41. Vellinga M, Wu P (2004) Low-latitude freshwater influences on centennial variability of the Atlantic thermohaline circulation. J Clim 17:4498–4511CrossRefGoogle Scholar
  42. Wang C, Lee SK, Enfield DB (2008a) Atlantic warm pool acting as a link between Atlantic multidecadal oscillation and Atlantic tropical cyclone activity. Geochem Geophys Geosyst 9:Q05V03. doi: 10.1029/2007GC001809 CrossRefGoogle Scholar
  43. Wang C, Lee SK, Enfield DB (2008b) Climate response to anomalously large and small Atlantic warm pools during the summer. J Clim 21:2437–2450CrossRefGoogle Scholar
  44. Yin J, Schlesinger ME, Andronova NG, Malyshev S, Li B (2006) Is a shutdown of the thermohaline circulation irreversible? J Geophys Res 111:D12104. doi: 10.1029/2005JD006562 CrossRefGoogle Scholar
  45. Zhang R (2007) Anticorrelated multidecadal variations between surface and subsurface tropical North Atlantic. Geophys Res Lett 34:L12713. doi: 10.1029/2007GL030225 CrossRefGoogle Scholar
  46. Zhang R, Delworth TL, Held I (2007) Can the Atlantic Ocean drive the observed multidecadal variability in Northern Hemisphere mean temperature? Geophys Res Lett 34:L02709. doi: 10.1029/2006GL028683 CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Physical Oceanography DivisionNOAA Atlantic Oceanographic and Meteorological LaboratoryMiamiUSA
  2. 2.Cooperative Institute for Marine and Atmospheric StudiesUniversity of MiamiMiamiUSA

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