How Ice Age Floods Sent Icebergs Sailing to Florida

Imagine icebergs as tall as the Eiffel Tower silently drifting by Florida's balmy beaches.

Add a few braying walruses, and mammoths grazing nearby on a broad coastal plain, and there's Ice Age Florida for you. And believe it or not, the icebergs are among the most indisputable parts of this picture.

During the last Ice Age, massive chunks of ice plowed deep grooves and furrows into the Atlantic seafloor from South Carolina to southern Florida. Named keel scours, after the V-shaped structures on boats, the features record the passage of massive glacial floods unleashed from Canada, according to a study published Sunday in the journal Nature Geoscience. The far-traveled floodwaters suggest that future ice sheet melting may be more complex than previously thought. [Gallery: An Expedition Into Iceberg Alley]

Image: Iceberg scours
Scientists say long grooves visible in the Atlantic seafloor were left behind by massive chunks of ice that plowed their way past South Carolina and Florida.

"We can't simply make the assumption that all of the cold, fresh water from ice sheet melting stays in the North Atlantic. Our results show that smaller, coastal currents can be very effective at redistributing this fresh water and impacting a much larger area," said lead study author Jenna Hill, a geologist at Coastal Carolina University.

The icebergs probably came from one of the huge glacial lakes that existed in northern North America when the ice sheets were at their peak, between 22,000 and 12,000 years ago. Ice dams walled off these glacial lakes from the ocean.

When the dams collapsed, floods of frigid freshwater spilled into the North Atlantic, carrying an enormous armada of icebergs. All that cold, fresh water sat on top of hotter, salty water, forcing the warm water to sink, scientists think. This shut down the natural ocean currents that keep the Northern Hemisphere warm. The rapid shift triggered a long cold snap.

Image: Currents
A map generated by a computer model shows the Ice Age coastal currents that could have carried icebergs south to Florida. Alan Condron

The discovery of icebergs in Florida suggests not all of the floodwaters went east. Some of the icy overflow headed south, beating back the warm Gulf Stream and insulating the icebergs on their journey southward.

"This actually has enormous implications for that model and for what triggers climate change," said study co-author Alan Condron, an oceanographer at the University of Massachusetts at Amherst.

— Becky Oskin, LiveScience

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