When icebergs floated off Key West…

Nature paints a more vivid picture of climate change – and the related changes in ocean currents – by retracing the paths of prehistoric icebergs in the years when the oceans were colder:

Their results show that some of the glacial floodwater running off North America formed a narrow current some 100 kilometres wide that flowed south along the continental shelf from the tip of present-day Newfoundland. Icebergs carried along by these flows would have reached South Carolina within a few months — and in some larger floods, would have reached Florida. The bergs would have been as large as some that calve from Greenland today, extending as far as 300 metres below the surface.

The model simulations help explain the presence of massive scars that have been found on the sea floor off the continental shelf, left by icebergs running aground. The team reports newly-discovered marks as far south as the Florida Keys, adding to the evidence for the idea that icebergs travelled into subtropical waters. These scour marks line up right along the flow of the simulated currents.

The work could help researchers understand how future climate change might affect ocean currents. The Greenland ice sheet is rapidly melting, and some researchers have worried that the influx of cold fresh water spreading across the North Atlantic could disrupt existing patterns of circulation such as the Gulf Stream.

Condron says that his results suggest that the Greenland meltwater could form a coastal current that reaches Newfoundland, injecting large amounts of fresh water directly into the North Atlantic Gyre, a powerful vortex of ocean currents. However, Florida pensioners need not worry about dodging icebergs in the Keys; the projected modern-day Greenwater meltwater flows would still be roughly 25 times smaller than the prehistoric ones that brought icebergs to Florida.