Stuart A. Cunningham talks
with ScienceWatch.com and answers a few questions
about this month's New Hot Paper in the field of
Article Title: Temporal variability of the Atlantic
meridional overturning circulation at 26.5 degrees
SA;Kanzow, T;Rayner, D;Baringer, MO;Johns,
WE;Marotzke, J;Longworth, HR;Grant, EM;Hirschi, JJM;Beal,
LM;Meinen, CS;Bryden, HL
Year: AUG 17 2007
* Natl Oceanog Ctr, Empress Dock, Southampton SO14 3ZH,
(addresses have been truncated)
Why do you think your paper is highly
The Atlantic meridional overturning circulation (AMOC)—see
Figure 1 below—carries 25% of the global
ocean-atmosphere northward heat flux and is important for maintaining the
moderate, maritime climate of the UK and western Europe. However,
paleoclimate observations suggest that the circulation has, in the past,
abruptly slowed in response to changes in forcing, leading to rapid cooling
for the UK and Europe.
Global coupled climate models (CGCM2) reported in the Intergovernmental
Planet on Climate Change (IPCC) 3rd and 4th assessment reports suggest a
25% slowing of the AMOC by 2100. Hence, it is uncertain whether there could
be a rapid or prolonged slowing of the AMOC in response to global warming.
Whilst in situ ocean observations have been able to define the
average strength of the AMOC, its variability on all timescales is
Logo of the RAPID-MOC/MOCHA project
: Monitoring the Atlantic Meridional Overturning
Circulation at 26.5¡N / Meridional
Overturning Circulation and Heat Flux
A paper published in Nature in 2005 (Bryden, HL, et al.,
"Slowing of the Atlantic Meridional Overturning Circulation at 26.5°N,"
Nature 438: 655-57, 2005) suggested—on the basis of five
snapshot measurements made over five decades—that the AMOC had
already slowed by 30%. The interpretation of slowing was highly
controversial because of the unknown size and frequency spectrum of the
Our paper has been highly cited because, for the first time, we have
demonstrated that continuous in situ ocean observations are able
to measure the AMOC on a daily basis. These observations will directly
address key uncertainties in the response of Earth's climate to
The slowing of the AMOC inferred from snapshot measurements was contained
within the variability of our first year of continuous observations.
Although the possibility of measuring an ocean-wide circulation was
controversial, we have demonstrated that it can be done. The results are
acting as a stimulus for ambitious new programs in basin-wide continuous
observations, and are critical for the evaluation of climate models.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Our paper describes both a new methodology along with the discoveries that
flowed from these new observations.
Would you summarize the significance of your paper
in layman's terms?
We demonstrate that it is possible to make efficient and accurate
measurements of a complex circulation on an ocean-wide scale. This is
leading to a new understanding of coupled ocean-atmosphere dynamics.
In particular, the data are now being used to critically evaluate the
realism of coupled climate models that predict future changes in the
Atlantic circulation. The system monitors interannual changes in the
circulation with a resolution of 8% of the mean. This means large, abrupt
changes should be readily observed. Ten years of uninterrupted measurements
will ensure that any seasonal cycles are well-defined and help refine the
nature of interannual variations, whether they are oscillations, trends, or
How did you become involved in this research, and
were there any problems along the way?
Professor Jochem Marotzke—now director of the Max Planck Institute
for Meteorology, Hamburg—joined the National Oceanography Centre,
Southampton in 2001. As a theorist and modeler, Professor Marotzke
stimulated the observationalists to think how the problem of continuous
AMOC observations could be tackled practically.
An international group was created (Figure 2), and coordinated proposals
were submitted to UK and US funding agencies. The international operational
team is led by Professor Bill Johns from the University of Miami, supported
by the National Science Foundation; Dr. Molly O. Baringer from the Atlantic
Oceanographic and Meteorological Laboratory, Miami, funded through the
National Oceanographic and Atmospheric Administration; Professor Harry
Bryden of the School of Ocean and Earth Sciences, University of
Southampton, and Dr. Stuart Cunningham, National Oceanography Centre,
Southampton, funded by the Natural Environment Research Council.
Where do you see your research leading in the
On a personal level I wish to continue researching how the AMOC is related
to climate forcing on longer timescales, so that we may better understand
the role of the ocean in climate.
Do you foresee any social or political
implications for your research?
Knowledge on the state of the AMOC, and the ability to detect any sudden
change, holds immediate political and societal benefit as the world
researches plans and adapts to climate change. Abrupt changes in the AMOC
have the potential to offset some, if not all, of the projected warming for
the 21st century. Therefore, the ability to detect such change is vital so
that the political and societal adaptive strategy is in line with (i.e.,
appropriate to) the level of expected warming.
Dr. Stuart Andrew Cunningham
National Oceanography Centre (NOCS)
University of Southampton
Southampton, Hants, UK
Keywords: Temporal variability, Atlantic meridional overturning
circulation, 26.5 degrees N, maritime climate of the UK and western
Europe, paleoclimate observations, global coupled climate models,
continuous in situ ocean observations, global warming, coupled
ocean-atmosphere dynamics, basin-wide continuous observations, seasonal
cycles, interannual variations.