Younger Dryas Water Drainage
In North America, in what is now southern Manitoba, a giant lake of glacial meltwater had formed to the west of the lobe of continental ice that protruded south into the central United States. This body of water, called Lake Agassiz, was larger than all the present Great Lakes combined. At first the water drained down the Mississippi into the Gulf of Mexico. But as the ice sheet retreated north, a new and shorter path to the sea was opened; through the Great Lakes Basin and into the St. Lawrence. Thirty thousand tons a second of freshwater began rushing into the North Atlantic from this new source, right into the northward-bound leg of the conveyor belt. All that freshwater substantially diluted the water in the conveyor. In fact, the sea water was no longer salty enough to sink to the ocean floor by the time it reached Greenland. Without that sinking, the conveyor was shut off, so was the heat the conveyor delivers to the North Atlantic region. The ice advanced again, and Dryas flowers began blooming again on the plains of northern Europe.