Atlantic Deep Water Reversal

Warm water sinks in the North Atlantic, forming a deep water current which flows southward at the bottom of the Atlantic all the way to Antarctica.  This has a profound effect on our climate - for example, contributing to the warm temperatures Europe enjoys despite its northernly latitude.  However, during the last Ice Age the deep Atlantic current may have actually been reversed, flowing instead from south to north.  See Reversed flow of Atlantic deep water during the Last Glacial Maximum in Nature.