2012: Advent Atmosphere: Great Lakes

by on December 10, 2012

The cold snap in Europe 12,000 years ago was caused by things warming up in North America.

Europe is warmed by an ocean current called the North Atlantic Drift, which is the Gulf Stream to you and me. For fairly complicated reasons, if there’s too much fresh water in the north atlantic, the Gulf Stream switches off or moves much further south, and Britain gets cold. Melting glaciers and ice caps put fresh water into the oceans, so the end of an ice age is a risky time for that warm current. And the Younger Dryas was indeed caused by melting ice, but it was far more sudden than just ice caps gradually melting. It was a sudden, dramatic influx of fresh water, and it came from the Great Lakes in North America.

The ice sheet melted unevenly in North America. The centre of the country was clearing of ice, but the route from the Great Lakes to the sea was still frozen over. The meltwater had nowhere to go, and it settled in the lakes, swelling them into a freshwater lake larger than anything in the modern day. When, finally, the Mackenzie River opened up, all that water rushed out into the Arctic Ocean. And the Gulf Stream went away, and Europe got cold, and stayed that way until the fresh water froze and the Gulf Stream came back, and then just as suddenly Europe warmed up again.

We’ll look at ocean currents in more detail tomorrow, along with their role in moving carbon dioxide out of the air.

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