Climate Models Reveal That Icebergs Once Reached As Far South As Florida

Chuck Bednar for redOrbit.com – Your Universe Online
As the massive ice sheet that once covered much of North America began to melt, icebergs and meltwater would have regularly reached South Carolina and even Florida, according to new research published in the current advance online edition of the journal Nature Geosciences.
As part of the study, University of Massachusetts Amherst oceanographer Alan Condron and his colleagues used new, high-resolution numerical models to describe ocean circulation during the last ice age (about 21,000 years ago). Their models, which are supported by newly-discovered iceberg scour marks along the continental shelf sea floor, imply that the climate change mechanics are more complex than previously believed.
“Our study is the first to show that when the large ice sheet over North America known as the Laurentide ice sheet began to melt, icebergs calved into the sea around Hudson Bay and would have periodically drifted along the east coast of the United States as far south as Miami and the Bahamas in the Caribbean, a distance of more than 3,100 miles, about 5,000 kilometers,” Condron said in a statement Sunday.
Condron and Jenna Hill of Coastal Carolina University analyzed high-resolution sea floor images from Cape Hatteras to Florida, and identified 400 scour marks on the seabed that would have been formed by gigantic icebergs plowing through sea floor mud. Those pits and grooves would have been formed as icebergs from the Laurentide ice sheet moved into shallow water, and their keels scraped along the ocean floor, the authors added.
“The depth of the scours tells us that icebergs drifting to southern Florida were at least 1,000 feet, or 300 meters thick,” Condron said. “This is enormous. Such icebergs are only found off the coast of Greenland today.”
In order to determine how these icebergs might have found their way as far south as Florida, the researchers simulated the release of a series of glacial meltwater floods in a high-resolution ocean circulation model at four different levels in two separate locations – Hudson Bay and the Gulf of St. Lawrence.
Their glacial ocean circulation model revealed that, in order for the icebergs to reach all the way to Florida, massive amounts of meltwater would have had to have been discharging from the Laurentide ice sheet in one of those two locations. The volume of water required would have to have been nearly equal to a catastrophic flood.
In addition, the surface ocean off the coast of Florida would have had to have undergone drastic changes during these meltwater events, the researchers added. They would have had to have undergone a 180-degree flip in direction, so that the warm, northward flowing Gulf Stream would have had to be replaced by a cold, southward flowing current, making it so that the water temperature would have dipped down to close to freezing.
According to Condron, this series of events would have resulted in the sudden appearance of massive icebergs along the eastern coast of the US reaching as far south as the Florida Keys. However, these events would have been abrupt and short-lived, lasting less than one full year.
“This new research shows that much of the meltwater from the Greenland ice sheet may be redistributed by narrow coastal currents and circulate through subtropical regions prior to reaching the subpolar ocean. It’s a more complicated picture than we believed before,” he explained.
He and Hill believe that future research into the mechanics of climate change should account for the role that coastal boundary currents play in redistributing ice sheet runoff and subpolar fresh water. Condon is a research assistant professor specializing in arctic climate modeling, while Hill is an assistant professor in marine geology.
Image 2 (below): This is a map showing the pathway taken by icebergs from Hudson Bay, Canada, to Florida. The blue colors (behind the arrows) are an actual snapshot from the authors’ high resolution model showing how much less salty the water is than normal. The more blue the color the less salty it is than normal. In this case, blue all the way along the coast shows that very fresh, cold waters are flowing along the entire east coast from Hudson Bay to Florida. Credit: UMass Amherst
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