“Snowbirds” they are called—people who escape snowy winters in the northern US by seasonally migrating to second homes in Florida. Probably about the last thing they would like to see while walking along the beach is the ice following them south. At certain times just a handful of millennia ago, it turns out, they might have been surprised to find icebergs floating by the beaches.

When Earth’s climate was colder and an ice sheet covered Canada, impressive flotillas of icebergs were occasionally launched into the Atlantic during incidents known as “Heinrich events.” Each time a batch of icebergs and glacial meltwater were vomited out, the area around the North Atlantic experienced climatic consequences. It’s thought that the infusion of freshwater gummed up the conveyor belt of Atlantic Ocean circulation, disrupting the transport of heat throughout the entire ocean basin.

Heinrich events are usually seen in ocean sediment cores as layers of gritty sediment dropped from melting icebergs onto the fine mud of the seafloor. That’s even been seen as far south as Bermuda. Closer to North America’s eastern coast, trenches carved by the undersides of large icebergs have been spotted in the mud off Nova Scotia, New Jersey, and even the Carolinas.

The Heinrich events have often been abstracted in climate model simulations as the dumping of a batch of freshwater straight into the North Atlantic conveyor. But recently, some work has been done to figure out the routes the water would have taken as it mixed into the complex currents of the Atlantic.

Coastal Carolina University’s Jenna Hill and University of Massachusetts, Amherst’s Alan Condron got their hands on some high-resolution maps of the seafloor from North Carolina down to Florida, and they found new iceberg trenches all along the way to the southern tip of the Sunshine State. The Gulf Stream pushes northward along the coast there today, so were the icebergs fighting the current to make a delivery to Florida? Not likely.

The researchers investigated with a climate model set up to simulate ocean circulation 20,000 years ago at the peak of the most recent reign of the glaciers. In that configuration, a shallow current flows south, hugging the coast, from Hudson Bay in Canada all the way to Cape Hatteras in North Carolina.

But to explain Titanic-killers reaching Florida, you have to account for the Heinrich event meltwater. The researchers simulated meltwater flows of varying sizes from Hudson Bay and the Gulf of St Lawrence, where the North American ice sheet would have been calving off icebergs. For the larger flows—and we're talking very large, double or more the normal global total of rivers flowing into the ocean—the freshwater strengthened the coastal current, pushing it south to Florida before submitting to the Gulf Stream. Naturally, it would have taken some icebergs along for the ride.

This makes sense given the iceberg scrapes they found in the seafloor. Near North Carolina, the tracks are 10 to 100 meters wide, 10 to 20 meters deep, and as long as 30 kilometers or more. Down by Florida, they’re smaller (2 to 5 meters deep) and less common. Icebergs 50 to 300 meters in thickness could have fairly routinely drifted as far as North Carolina, but it would have taken a large Heinrich event to carry them as far as Florida.

The icebergs that made it to Florida would have had to be a little smaller as well. That’s because the south-flowing coastal current was fresher water and sat at the surface in the model. Beneath it, there was still a current moving to the north. Thick icebergs, then, would have had keels that extended down into the water flowing in the opposite direction. The bigger the iceberg, the stronger the south-flowing current that would have been needed to overcome the drag.

Apart from explaining some curious seafloor gouges, the study also provides a little insight into how all that cold freshwater might have interacted with Atlantic Ocean circulation. It seems some of the water would have travelled quite far to the south before mixing in with the Gulf Stream and drifting back to the northern Atlantic. That means it would be more diluted by the salty seawater before it reached the area where the ocean conveyor belt sinks downward.

The work shows how much the Heinrich events reset the pattern of Atlantic circulations, creating one that includes at least a few frozen Canadians hitting Florida’s coast to thaw out.

Nature Geoscience, 2014. DOI: 10.1038/NGEO2267 (About DOIs).