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The researchers have established a unique system of observational instruments that will help to provide early detection of change in the Atlantic Meridional Overturning Circulation (MOC), also known as the Ocean Conveyor Belt. The system will help scientists to verify simulations of the MOC from climate models, and to produce more realistic climate change predictions, which are essential for the development of adaptation plans.

In March 2004, as part of the UK Natural Environment Research Council's £20m RAPID Climate Change Programme and the US National Science Foundation MOCHA project, the scientists deployed an instrument array across the Atlantic from the Saharan coast of Africa to the Bahamas.

Since then, the instruments have provided a continuous record of the salinity, temperature and density of the ocean. In combination with current measurements of the Gulf Stream in the Straits of Florida (provided by scientists from the US National Oceanic & Atmospheric Administration) and satellite measurements of the wind-driven flow across 26°N, the MOC has been calculated on a daily basis.

First Year Results
Analyses of the first year's data are published this week in the journal Science, with papers from Dr Stuart Cunningham and Dr Torsten Kanzow of the National Oceanography Centre, Southampton (NOCS).

Their work shows that the remarkable instrument array is working effectively and is bringing in some surprising results, demonstrating that it provides a major contribution to the global climate observing system. The continuous monitoring of the ocean over a full year has pinpointed some major variations in the vertical structure of the Atlantic circulation.

Dr Cunningham said:
"The most astonishing event occurred in early November 2004 when the southward, colder flow of deep water essentially stopped completely. However, the flow at upper levels increased to compensate this reduction in deep flow, so there was no overall change at that time. The array is providing unprecedented observations of the range of ocean variability. The impact of these variations for global and regional climate can now be investigated."

Measuring Variability
The full range of variability measured in the Atlantic MOC is large. It can range from as little as 4 million tonnes of water to as much as 35 million tonnes of water a second. The year-long average of the MOC calculates at around 19 million tonnes of water, which tallies with earlier estimates.

With the RAPID array it is, however, feasible to monitor the annual average MOC in greater detail. This would be sufficient to detect any large, abrupt changes in the circulation, critical to planning for future climate change.

Dr Steven Wilson, Director of Science & Innovation for NERC, said:
"Funding this ambitious project was a high risk as nothing like it had ever been done before but, through very strong international collaboration, it has paid off and is providing some spectacular results. Understanding the climate is a very high priority for NERC."