Seasonal variability of the Atlantic meridional overturning circulation at 26.5°N

T. Kanzow, S. A. Cunningham, W. E. Johns, J. J.M. Hirschi, J. Marotzke, M. O. Baringer, C. S. Meinen, M. P. Chidichimo, C. Atkinson, L. M. Beal, H. L. Bryden, J. Collins

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189 Scopus citations


The Atlantic meridional overturning circulation (AMOC) makes the strongest oceanic contribution to the meridional redistribution of heat. Here, an observation-based, 48-month-long time series of the vertical structure and strength of the AMOC at 26.5°N is presented. From April 2004 to April 2008, the AMOC had a mean strength of 18.7±2.1 Sv (1 Sv≡106 m3 s-1)with fluctuations of 4.8 Sv rms. The best guess of the peak-to-peak amplitude of theAMOCseasonal cycle is 6.7 Sv, with a maximum strength in autumn and a minimum in spring. While seasonality in the AMOC was commonly thought to be dominated by the northward Ekman transport, this study reveals that fluctuations of the geostrophic midocean and Gulf Stream transports of 2.2 and 1.7 Sv rms, respectively, are substantially larger than those of the Ekman component (1.2 Sv rms). A simple model based on linear dynamics suggests that the seasonal cycle is dominated by wind stress curl forcing at the eastern boundary of the Atlantic. Seasonal geostrophic AMOC anomalies might represent an important and previously underestimated component of meridional transport and storage of heat in the subtropical North Atlantic. There is evidence that the seasonal cycle observed here is representative of much longer intervals. Previously, hydrographic snapshot estimates between 1957 and 2004 had suggested a longterm decline of the AMOC by 8 Sv. This study suggests that aliasing of seasonal AMOC anomalies might have accounted for a large part of the inferred slowdown.

Original languageEnglish (US)
Pages (from-to)5678-5698
Number of pages21
JournalJournal of Climate
Issue number21
StatePublished - Nov 2010


  • Atlantic Ocean
  • Meridional overturning circulation
  • Seasonal variability
  • Transport
  • Wind stress

ASJC Scopus subject areas

  • Atmospheric Science


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