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Summary
On December 1st, 2005, Prof. Bryden and his team reported in Nature (Bryden et
al., 2005. Slowing of the Atlantic meridional overturning circulation at 25N.
Nature 438,
655-657:http://www.nature.com/nature/journal/v438/n7068/edsumm/e051201-11.html
) that the Atlantic meridional overturning circulation (MOC) seems to have
weakened by about 30% in the last ... decade or so.

The team analyzed measurements taken along a line at about 25N from the Bahamas
to Morocco in 2004, and compared these to measurements taken along
approximately this line in 1957, 1981, 1992 and 1998. The results suggest that
the Gulf Stream flow across 25N has remained nearly constant in this period,
but the MOC has slowed from about 20 Sv in 1957 to 14 Sv in 2004.

The evidence for the slow-down can be found both in the increase in southward
recirculation of warm water in the surface layer, and in a decrease in
southward transport of lower North Atlantic Deep Water between 3000 and 5000m
depth.

Some climate models have suggested that we could expect such a slowdown as a
result of global warming, and that this could cool northwest Europe by a few
degrees C, with the change happening relatively fast, perhaps over just a
decade. These measurements are evidence that the models could be right.

The five sections are just "snapshots" and cannot tell us for sure whether the
changes are a result of natural variability. Very little is known about how the
MOC varies seasonally or from year to year. To be sure that the observed change
is the result of a long-term trend rather than natural fluctuations we will
need to monitor flow across 25N continuously for about a decade.

In April 2004 Prof. Bryden's team deployed an array of instruments across the
Atlantic at 25 N. The array measures temperature, salinity, currents and
pressure. The first full year of measurements were collected in April 2005, and
analysis of this data is now underway.
See: http://www.noc.soton.ac.uk/rapid/sis/moc_monitor.php

Geographic Coverage Spatial coordinates   

N: 25.0

S: 25.0

E: -10.0

W: -75.0

Data Set Citation

Dataset Creator: Bryden, H., H. Longworth, S. Cunningham Dataset Title: Slowing of the Atlantic meridional overturning circulation at 25N. Dataset Release Date: 1 December 2005 Dataset Publisher: Nature Issue Identification: 438, pp. 655-657 Online Resource: http://www.noc.soton.ac.uk/rapid/sis/moc_monitor.php

Temporal Coverage

Start Date: 1957-01-01 Stop Date: 2004-12-31

Location Keywords

OCEAN > ATLANTIC OCEAN > NORTH ATLANTIC OCEAN OCEAN > ATLANTIC OCEAN

Science Keywords

OCEANS > OCEAN CIRCULATION > OCEAN MIXED LAYER OCEANS > OCEAN CIRCULATION > THERMOHALINE CIRCULATION OCEANS > OCEAN CIRCULATION > UPWELLING/DOWNWELLING OCEANS > OCEAN TEMPERATURE > OCEAN MIXED LAYER OCEANS > OCEAN TEMPERATURE > THERMOCLINE OCEANS > OCEAN TEMPERATURE > WATER TEMPERATURE OCEANS > SALINITY/DENSITY > HALOCLINE OCEANS > SALINITY/DENSITY > SALINITY OCEANS > SALINITY/DENSITY > SALT TRANSPORT

ISO Topic Category

CLIMATOLOGY/METEOROLOGY/ATMOSPHERE OCEANS

Platform

SHIPS BUOYS

Instrument

CTD > Conductivity, Temperature, Depth

Project

RAPID > RAPID CLIMATE CHANGE

Access Constraints
Currently access to data restricted to RAPID investigators. Graphs and tables
are available.

Ancillary Keywords

rapid climate change abrupt climate change MOC Atlantic Meridional Overturning Circulation Atlantic heat conveyor Atlantic conveyor belt THC

Data Set Progress

IN WORK

Originating Center

SOC

Data Center

Raid Climate Change, Southampton Oceanography Centre, University of Southampton Data Center URL: http://www.noc.soton.ac.uk/rapid/rapid.php Data Center Personnel Name: VALBORG BLYFELD Phone: +44 (0) 23 8059 6405 Fax: +44 (0) 23 8059 6400 Email: valborg at noc.soton.ac.uk Contact Address: James Rennell Division for Ocean Circulation and Climate Room 254/30 Southampton Oceanography Centre (SOC) Empress Dock City: Southampton Postal Code: SO14 3ZH Country: United Kingdom

Personnel

HARRY BRYDEN Role: INVESTIGATOR Contact Address: National Oceanography Centre University of Southampton Waterfront Campus European Way City: Southampton Postal Code: SO14 3ZH Country: United Kingdom HANNAH LONGWORTH Role: INVESTIGATOR Contact Address: National Oceanography Centre University of Southampton Waterfront Campus European Way City: Southampton Postal Code: SO14 3ZH Country: United Kingdom STUART CUNNINGHAM Role: INVESTIGATOR Contact Address: National Oceanography Centre University of Southampton Waterfront Campus European Way City: Southampton Postal Code: SO14 3ZH Country: United Kingdom

Related URL

Link: GET DATA Description: Access to graphs and documentation. Restricted access to data Link: GET DATA Description: Get supplemental graphs from the Nature article Link: VIEW PROJECT HOME PAGE Description: RAPID: Rapid climate change project Link: VIEW RELATED INFORMATION Description: Related information on the Atlantic conveyor

Publications/References
Bryden et al., 2005. Slowing of the Atlantic meridional overturning
circulation at 25°N. Nature 438, 655-657.

Creation and Review Dates

DIF Creation Date: 2005-12-22 Last DIF Revision Date: 2005-12-22

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