Trigger for Earth’s Last Big Freeze Identified
For more than 30 years, climate scientists have debated whether flood waters from melting of the enormous Laurentide Ice Sheet, which ushered in the last major cold episode on Earth about 12,900 years ago, flowed northwest into the Arctic first, or east via the Gulf of St.Lawrence, to weaken ocean thermohaline circulation and have a frigid effect on global climate.
Now, geoscientist Alan Condron, using new, high-resolution global ocean circulation models, reports the first conclusive evidence that this flood must have flowed north into the Arctic first down the Mackenzie River valley. The research team also shows that if it had flowed east into the St. Lawrence River valley, Earth’s climate would have remained relatively unchanged. “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 Condron of UMass Amherst’s Climate System Research Center. Findings appear in the current issue of Proceedings of the National Academy of Sciences.