monitoring the atlantic overturning circulation

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A decade of RAPID observations yields a few surprises

MOC schematic with RAPID moorings

The RAPID MOC array at 26°N.   Larger figure

moc plot

AMOC time-series 2004-2014. Larger figure

In April 2014 the time-series of RAPID observations of the Atlantic meridional overturning circulation (AMOC) at 26°N reached ten years. The decade of observations have led to a better understanding of the AMOC and how it varies on different time scales.

Until RAPID our understanding of the AMOC was based on sparse ship-based observations, including 5 research cruises to the region in 1957, 1981, 1992, 1998 and 2004. In the light of AMOC estimates from this work, the RAPID time-seres brought a number of surprises:

  1. More variation than expected: The range of AMOC variability over a year was much greater than previously expected from ship-based observations. Later a similar range has been found at 34.5°S.
  2. A marked seasonal cycle: There is a marked seasonal cycle, and the difference between the spring minimum and the autumn maximum (~6.7Sv) is also much larger than originally anticipated.
  3. Extreme decline in 2009-10: During winter 2009-10 there was a totally unexpected decline in the AMOC of about 30% - far greater than the range of interannual variability found in the climate models used for the IPCC assessments. The decline was also seen in data from Argo floats and satellite altimetry. The event coincided with a negative NAO index, and led to an extreme sea level rise off the east coast of the US. It was also associated with an unusually cold winter in Western Europe.
  4. Gradual AMOC decline: Over decade of 26.5°N observations, the AMOC has been declining at a rate of about 0.5 Sv per year, 10 times as fast as predicted by climatemodels. It is too early to say wheter this is an on-going trend caused by global warming, or whether it is part of the decadal variability known as the Atlantic Multidecadal Oscillation.

Download the RAPID data

After quality control and initial analysis the RAPID data from 26°N is made available to the scientific community through the British Oceanographic Data Centre (BODC) and from the project web site. To download the data follow the link to the data download page, and fill in the form.

Other AMOC measurements

There have also been other ongoing measurements that capture components of the AMOC. Some are not continuous; others are of much shorter duration. Combined with the RAPID data from 26°N, these observations are leading to a more complete picture of the AMOC and have altered our view of the role played by ocean variability in climate.

Further AMOC observing systems are being developed, both to the north in the North Atlantic subpolar gyre, and to the south, in the South Atlantic. Together these will give a holistic picture of the AMOC from south to north - and almost certainly yield further surprises.


Bryden, H.L., King, B.A., McCarthy, G.D., McDonagh, E.L. (2014): Impact of a 30% reduction in Atlantic meridional overturning during 2009-2010, Ocean Sci., 10: 683-691. doi:10.5194/os-10-683-2014

Goddard, P. B., Yin, J., Griffies, S. M., Zhang, S. (2015): An extreme event of sea-level rise along the Northeast Coast of North America in 2009-2010. Nat. Commun. 6, 6346 (2015). doi: 10.1038/ncomms7346

McCarthy, G.D., Haigh, I.D., Hirschi, J. J.-M., Grist, J.P., Smeed, D.A. (2015): Ocean impact on decadal Atlantic climate variability revealed by sea-level observations, Nature, 521, 508-510. doi:10.1038/nature14491

McCarthy, G.D., Smeed, D.A., Johns, W.E., Frajka-Williams, E., Moat, B.I., Rayner, D., Baringer, M.O., Meinen, C.S., Collins, J., Bryden, H.L. (2015): Measuring the Atlantic Meridional Overturning Circulation at 26°N, Progress in Oceanography, 130, 91-111. doi:10.1016/j.pocean.2014.10.006

Srokosz, M.A., Bryden, H.L. (2015): Observing the Atlantic Meridional Overturning Circulation yields a decade of inevitable surprises, Science, 348 (6241). doi:10.1126/science.1255575

MOC schematic with RAPID moorings at the western and eastern boundaries and the Mid-Atlantic Ridge

Schematic of the Atlantic meridional overturning circulation with the RAPID moorings. Credit: NOC

plot of amoc data

10-year time series of the AMOC measured at 26.5°N from April 2004 to March 2014. The gray line represents the 10-day filtered measurements, and the red line is the 180-day filtered time series. The seasonal cycle, the low AMOC event in 2009-2010 and the overall decrease in strength over the 10 years are all clearly visible.

plot of amoc data

A view of the back deck of the RRS James Cook during the RAPID cruise in April 2014. Photo: Ben Moat

The blog 10 years of RAPID follows the research cruise on RRS James Cook which completed the decade-long AMOC time-series in April 2014.