Huge icebergs used to drift down America’s coast as far as Florida just 31,000 years ago, a new study has shown.
Geographers used seafloor mapping to analyse 700 distinctive “plough marks” – or "scours" – on ocean floors, left behind by vast icebergs scraping through ocean sediment.
The researchers used these to track the path of the icebergs from Cape Hatteras, North Carolina, to the Florida Keys.
The discovery of icebergs in the area will offer researchers a new understanding of the interactions between icebergs and climate.
Woods Hole Oceanographic Institution (WHOI) climate modeler Dr Alan Condron said: “The idea that icebergs can make it to Florida is amazing.
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“The appearance of scours at such low latitudes is highly unexpected not only because of the exceptionally high melt rates in this region, but also because the scours lie beneath the northward flowing Gulf Stream.
“We recovered the marine sediment cores from several of these scours, and their ages align with a known period of massive iceberg discharge known as Heinrich Event 3.
“We also expect that there are younger and older scours features that stem from other discharge events, given that there are hundreds of scours yet to be sampled.”
Condron and his team developed a numerical iceberg model that simulates how icebergs drift and melt in the ocean.
The model shows that icebergs can only reach the scour sites when massive amounts of glacial meltwater (or glacial outburst floods) are released from Hudson Bay.
Condron said, “These floods create a cold, fast flowing, southward coastal current that carries the icebergs all the way to Florida.
“The model also produces 'scouring' on the seafloor in the same places as the actual scours.”
The ocean water temperatures south of Cape Hatteras are about 20-25C.
According to Condron, for icebergs to reach the subtropical scour locations in this region, they must have drifted against the normal northward direction of flow – the opposite direction to the Gulf Stream.
This indicates that the transport of icebergs to the south occurs during large-scale, but brief, periods of meltwater discharge.
Condron said, “What our model suggests is that these icebergs get caught up in the currents created by glacial meltwater, and basically surf their way along the coast.
"When a large glacial lake dam breaks, and releases huge amounts of fresh water into the ocean, there’s enough water to create these strong coastal currents that basically move the icebergs in the opposite direction to the Gulf Stream, which is no easy task.”
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