Timing of iceberg scours and massive ice-rafting events in the subtropical North Atlantic

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Iceberg tracks in the seafloor: Icebergs can travel south all the way to Florida!

Today, towering white objects floating off the Florida Keys are more likely to be cruise ships than anything else. But 30,000 years ago, giant icebergs drifted from Canada to as far south as Florida, a new study finds.

The study, published in the journal Nature Communications by researchers from Woods Hole Oceanographic Institution and USGS, documents the drifting of enormous icebergs down the North Atlantic coast during glacial flooding events.

The researchers found that during the Last Glacial Period 30,000 years ago, icebergs perhaps as tall as the Eiffel Tower drifted south along the Atlantic coast of North America, ferried along by cold-water currents created during periods of catastrophic glacial melting. These currents, likely caused by glacial ice dams bursting and releasing vast quantities of freshwater, would have been powerful enough to push the ice south, against the prevailing Gulf Stream.

“We’ve long suspected that these melting events could bring icebergs this far south,” said research geologist Jenna Hill, co-author of the study. “Our work now provides strong evidence for this and tells us when this happened.”

The ice left scour marks on the seafloor as it was pushed by the current. To determine the age of the scours, the researchers sailed to South Carolina and extracted sediment cores of sand and shells from the sea floor. They then used radiocarbon dating on the tiny, ancient shells (from single-celled creatures known as Foraminifera) in the sediment to figure out when the icebergs left their mark on the seafloor.

The study demonstrates that when large volumes of ice melt from a glacier, it can create currents that hug the coast and bring cold, fresh water full of icebergs to far-off parts of the ocean.

This work provides the first age constraints for so-called Floridian icebergs and suggests a new way to think about how icebergs and meltwater moved in the North Atlantic. The transit of these erstwhile icebergs has implications for global ocean circulation and climate, the study argues, as glacial ice today is receding across much of the globe. 

The view moves along an illustration of the seafloor that shows features like scours and basins.

These 3D perspective views of the seafloor bathymetry from multibeam sonar offshore of South Carolina show numerous grooves carved by drifting icebergs. As iceberg keels plow into the seafloor, they dig deep grooves that push aside boulders and piles of sand and mud along their tracks. Sediment cores from nearby buried iceberg scours were used to determine when these icebergs travelled south along the coast. Credit: Jenna Hill, U.S. Geological Survey, Pacific Coastal and Marine Science Center

Photograph looking closely at sand and silt collected in a long wide tube.

A sediment core, collected from the seafloor offshore of South Carolina, shows a coarser sediment layer covering finer sediment with a very distinct boundary.

(Credit: Jenna Hill, USGS Pacific Coastal and Marine Science Center. Public domain.)

 

 

 

 

People stand around a long apparatus on the deck of a large ship.

Scientists extract a core of sediment from a coring device.

(Credit: Jenna Hill, USGS Pacific Coastal and Marine Science Center. Public domain.)

People stand around a long apparatus on the deck of a large ship.

Scientists extract a core of sediment from a coring device.

(Credit: Jenna Hill, USGS Pacific Coastal and Marine Science Center. Public domain.)

 

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