In any case, the most common explanation of the event is that, as the ice-sheets retreated North, ice-dams holding in the Eastern edge of pro-glacial Lake Agazziz gave way and spewed vast amounts of cold water through the St. Lawrence river, where it caused a shut-down of the North Atlantic thermocline (sometimes called the great ocean conveyor) which carries warm water Northward via the Gulf Stream. This in turn caused Northern Hemisphere temperatures to plunge, glaciers to advance again, and so on and so forth.
Now, however, a new theory suggests a quite different route for this pulse of cold water. Instead of running East,
...geologists now believe they have found traces of this flood, revealing that cold water from North America's dwindling ice sheet poured into the Arctic Ocean, from where it ultimately disrupted climate-warming currents in the Atlantic.
In any case, you can read the whole thing through the link. As an aside, Nature, the magazine in which this new research was published, has just moved its news site outside of its pay wall. Lotsa fun there.