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Monitoring the Atlantic Meridional Overturning Circulation

Record type: Article

The rapid climate change programme (RAPID) has established a prototype system to continuously observe the strength and structure of the Atlantic meridional overturning circulation (MOC) at 26.5°N. Here we provide a detailed description of the RAPID-MOC monitoring array and how it has evolved during the first four deployment years, as well as an overview of the main findings so far. The RAPID-MOC monitoring array measures: (1) Gulf Stream transport through Florida Strait by cable and repeat direct velocity measurements; (2) Ekman transports by satellite scatterometer measurements; (3) Deep Western Boundary Currents by direct velocity measurements; (4) the basin wide interior baroclinic circulation from moorings measuring vertical profiles of density at the boundaries and on either side of the Mid-Atlantic Ridge; and (5) barotropic fluctuations using bottom pressure recorders. The array became operational in late March 2004 and is expected to continue until at least 2014. The first 4 years of observations (April 2004–April 2008) have provided an unprecedented insight into the MOC structure and variability. We show that the zonally integrated meridional flow tends to conserve mass, with the fluctuations of the different transport components largely compensating at periods longer than 10 days. We take this as experimental confirmation of the monitoring strategy, which was initially tested in numerical models. The MOC at 26.5°N is characterised by a large variability—even on timescales as short as weeks to months. The mean maximum MOC transport for the first 4 years of observations is 18.7 Sv with a standard deviation of 4.8 Sv. The mechanisms causing the MOC variability are not yet fully understood. Part of the observed MOC variability consists of a seasonal cycle, which can be linked to the seasonal variability of the wind stress curl close to the African coast. Close to the western boundary, fluctuations in the Gulf Stream and in the North Atlantic Deep Water (NADW) coincide with bottom pressure variations at the western margin, thus suggesting a barotropic compensation. Ongoing and future research will put these local transport variations into a wider spatial and climatic context.

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Citation

Rayner, Darren, Hirschi, Joël J.-M., Kanzow, Torsten, Johns, William E., Wright, Paul G., Frajka-Williams, Eleanor, Bryden, Harry L., Meinen, Christopher S., Baringer, Molly O., Marotzke, Jochem, Beal, Lisa M. and Cunningham, Stuart A. (2011) Monitoring the Atlantic Meridional Overturning Circulation Deep Sea Research Part II: Topical Studies in Oceanography, 58, (17-18), pp. 1744-1753. (doi:10.1016/j.dsr2.2010.10.056).

More information

Published date: September 2011
Keywords: Physical oceanography, Thermohaline circulation, Ocean circulation, Ocean currents, Mooring systems, Atlantic meridional overturning circulation
Organisations: Marine Systems Modelling, Marine Physics and Ocean Climate

Identifiers

Local EPrints ID: 174949
URI: http://eprints.soton.ac.uk/id/eprint/174949
ISSN: 0967-0645
PURE UUID: 22fb95d5-6bb8-4ca7-85f2-561c4a67d8b6
ORCID for Eleanor Frajka-Williams: ORCID iD orcid.org/0000-0001-8773-7838
ORCID for Harry L. Bryden: ORCID iD orcid.org/0000-0002-8216-6359

Catalogue record

Date deposited: 18 Feb 2011 11:30
Last modified: 18 Jul 2017 12:10

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Contributors

Author: Darren Rayner
Author: Joël J.-M. Hirschi
Author: Torsten Kanzow
Author: William E. Johns
Author: Paul G. Wright
Author: Harry L. Bryden ORCID iD
Author: Christopher S. Meinen
Author: Molly O. Baringer
Author: Jochem Marotzke
Author: Lisa M. Beal
Author: Stuart A. Cunningham

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