About 13,000 years ago, the Earth was plunged into what is called the 'Big Freeze' — or more formally known as the 'Younger Dryas stadial' — where the planet's climate cooled significantly, ushering in a new glacial period that lasted for about 1,300 years.
It has been well-established that the Big Freeze was caused when a lake of melt-water sitting on the Laurentide Ice Sheet — a 2-3 km thick sheet of ice that covered most of the land-mass of what is now Canada and parts of the U.S. Midwest — broke through an ice-damn and rushed into the north Atlantic. This massive influx of frigid fresh water into the ocean disrupted the global circulation of heat and salt-content in the oceans, and quickly altered the Earth's climate.
"This episode was the last time the Earth underwent a major cooling, so understanding exactly what caused it is very important for understanding how our modern-day climate might change in the future," says Alan Condron, a physical oceanographer with the University of Massachusetts Amherst's Climate System Research Center, according to Science Daily.
There has been some debate over the years as to the path of this fresh water, though. The most commonly used hypothesis, first proposed by Wallace Broecker of Columbia University in 1989, was that the water flowed down the St. Lawrence River into the north Atlantic. Others suggested that it took a route down the Mackenzie River basin and into the Arctic Ocean. Now, Condron and research partner Peter Winsor, from the University of Alaska Fairbanks, have developed a new high-resolution ocean-ice circulation computer model that shows strong support for the latter idea.
This computer model, the most powerful so far created, runs on a supercomputer at the National Energy Research Science Computing Center in Berkeley, California. "With this higher resolution modeling, our ability to capture narrow ocean currents dramatically improves our understanding of where the fresh water may be going." said Condron and Winsor.
"The results we obtain are only possible by using a much higher computational power available with faster computers. Older models weren't powerful enough to model the different pathways because they contained too few data points to capture smaller-scale, faster-moving coastal currents." added Condron.
Condron and Winsor's simulations showed that were the waters from the Laurentide ice sheet to have flowed down the St. Lawrence, they would have entered the Atlantic Ocean waters around 3000 kilometres too far south to have disrupted the ocean circulation enough to cause the Big Freeze. However, simulations showing the water flowing into the Arctic Ocean via the Mackenzie river basin showed that the currents in the Arctic Ocean would have transported the cold, fresh waters to exactly where they were needed to cause the event — the sub-polar Atlantic Ocean, off the coast of Greenland.
"Dumping water in the Arctic is a very efficient way to … cool the Northern Hemisphere," says W. Richard Peltier, according to Science News. Peltier is a professor of physics at the University of Toronto, and director of UofT's Centre for Global Change Science.
Although Broecker's hypothesis had wide support, there was a lack of physical evidence along the St. Lawrence River, however there is evidence in boulders and gravel along the Mackenzie River basin that supports the idea of a massive flood around the time of the Big Freeze.
"This whole thing now hangs together beautifully," said Peltier.
"Our results are particularly relevant for how we model the melting of the Greenland and Antarctic Ice sheets now and in the future," said Condron. "It is apparent from our results that climate scientists are artificially introducing fresh water into their models over large parts of the ocean that freshwater would never have reached. In addition, our work points to the Arctic as a primary trigger for climate change. This is especially relevant considering the rapid changes that have been occurring in this region in the last 10 years."