Editor's Summary

1 December 2005

Atlantic Ocean trends


The circulation across the 25° N latitude line in the Atlantic Ocean between Africa and the Bahamas has become the benchmark for estimating the Atlantic meridional overturning circulation, an important component of global ocean transport that carries warm upper waters into far northern latitudes via the Gulf Stream and returns cold deep waters south across the Equator. Its heat transport contributes to the moderate climate of maritime and continental Europe. A new hydrographic section across 25° N was taken in 2004, and comparison with measurements from 1957, 1981, 1992 and 1998 reveals a slowing of almost a third between 1957 and 2004. This means that more Gulf Stream waters are now recirculating southwards at mid-ocean depths, and that southward transport of cold lower North Atlantic Deep Water has halved. Some climate models suggest that the anthropogenic increase in atmospheric CO2 will result in a slowdown of the Atlantic overturning circulation, so this latest finding will add fuel to the debate on climate change.

News and ViewsOceanography: The Atlantic heat conveyor slows

Computer simulations predict that global warming will weaken the ocean circulation that transports heat from the tropics to higher latitudes in the North Atlantic. Such an effect has now been detected.

Detlef Quadfasel

doi:10.1038/438565a

LetterSlowing of the Atlantic meridional overturning circulation at 25° N

Harry L. Bryden, Hannah R. Longworth and Stuart A. Cunningham

doi:10.1038/nature04385

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