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Bursting American lakes chilled Europe

Bursting American lakes chilled Europe

作者:向氧  时间:2019-03-07 10:03:11  人气:

By Fred Pearce A GREAT flood in North America cooled the climate of Europe for hundreds of years, says a geologist in Colorado. He has tied together evidence that the sudden draining of two lakes in central Canada disrupted the circulation of oceans and chilled Europe by about 3 °C. Geologists know that more than 8000 years ago, two vast freshwater lakes in central Canada burst. The two lakes formed at the end of the last ice age, when meltwater from the great North American ice sheet was trapped by ice in Hudson Bay to the north. Eventually, more than 2000 years after the thaw began, the ice gave way. The water roared through the Hudson Strait and into the North Atlantic. A layer of sediment half a metre thick from the outflow still lies on the floor of the Hudson Strait. And plankton trapped in sediments from that time reveals a dramatic decline in the salinity of water in the Labrador Sea between Canada and Greenland. Donny Barber of the University of Colorado and his colleagues have now dated these sediments and calculated how much fresh water was released from the lakes. They estimate that 200 000 cubic kilometres of water—three times the amount of water in today’s North Sea—rushed into the ocean, raising sea levels worldwide by 30 centimetres. Barber argues that the rush of freshwater almost certainly disrupted the oceans and caused a previously unexplained cooling around the North Atlantic at this time, during which temperatures fell by up to 3 °C in Europe ( Nature, vol 400, p 344). “The world’s ocean circulation was hammered by the sudden freshwater influx,” says Barber. Normally, seawater in the North Atlantic freezes in winter. Because ice formation does not capture salt, the remaining seawater becomes increasingly saline and dense. It sinks to the ocean floor, and warm water from the south pours in to replace it,