The Atlantic meridional overturning circulation carries warm upper waters into far-northern latitudes and returns cold deep waters southward across the Equator. Its heat transport makes a substantial contribution to the moderate climate of maritime and continental Europe, and any slowdown in the overturning circulation would have profound implications for climate change.
Slowing of the Atlantic meridional overturning circulation at 25° N
by Harry L. Bryden , Hannah R. Longworth & Stuart A. Cunningham
nature
1 December 2005
http://www.nature.com/nature/journal/v438/n7068/abs/nature04385.html