Icebergs drifting from Canada to South Florida – cotton wool?

These 3-D perspective views of the bathymetry of the ocean floor from multibeam sonar off the coast of South Carolina reveal numerous grooves carved out by drifting icebergs. When iceberg keels plow into the ocean floor, they dig deep grooves that push aside boulders and piles of sand and mud along their tracks. Sediment cores from nearby buried icebergs were used to determine when these icebergs migrated south along the coast. Source: Jenna Hill, US Geological Survey, Pacific Coastal & Marine Science Center

WHOI has published the following press release on icebergs and ice ages.

From Woods Hole Oceanographic Institution

June 16, 2021

Data from the Woods Hole Oceanographic Institution and the United States Geological Survey show how icebergs drifted more than 5,000 km away during the last glaciation

Woods Hole, MA (June 16, 2021) – The Woods Hole Oceanographic Institution (WHOI) climate modeler, Dr. Alan Condron, and United States Geological Survey (USGS) research geologist Dr. Jenna Hill have found evidence that massive icebergs from about 31,000 years ago drifted more than 5,000 km (> 3,000 miles) along the east coast of the United States, from northeast Canada to south Florida. These results were published today in Nature Communications.

Using high-resolution ocean floor mapping, radiocarbon dating, and a new iceberg model, the team analyzed approximately 700 iceberg breakthroughs (“plow marks” on the ocean floor left by the lower portions of icebergs drawn by ocean sediments) from Cape Hatteras, North Carolina to Florida Key. The discovery of icebergs in this area opens a door to understanding the interactions between icebergs / glaciers and the climate.

“The idea that icebergs can make it all the way to Florida is amazing,” said Condron. “The occurrence of scour at such low latitudes is highly unexpected not only because of the extraordinarily high melt rates in this region, but also because the scour lies under the Gulf Stream flowing north.”

“We recovered the marine sediment cores from several of these scouring pools, and their ages coincide with a known period of massive iceberg runoff known as Heinrich Event 3. We also assume that there are younger and older scour features that stem from other runoff events. that there are hundreds of runs left to be sampled, ”added Hill.

To study how icebergs reached the scour sites, Condron 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 if massive amounts of glacial meltwater (or glacial eruptions) are released from Hudson Bay. “These floods create a cold, fast-flowing coastal current southwards that carries the icebergs all the way to Florida,” says Condron. “The model also creates ‘rubbers’ on the seabed in the same places as the actual ‘rubbers'”

Sea water temperatures south of Cape Hatteras are around 20-25 ° C (68-77 ° F). According to Condron and Hill, in order to reach the subtropical scour sites in this region, icebergs must have drifted north against the normal direction of flow – the opposite direction to the Gulf Stream. This suggests that icebergs are transported south during large-scale but short-term meltwater runoff.

“Our model suggests that these icebergs get caught in the meltwater currents of the glaciers and are basically surfing along the coast. When a large glacial lake dam breaks and releases huge amounts of fresh water into the ocean, there is enough water to create those strong coastal currents that basically move the icebergs in the opposite direction to the Gulf Stream, which is no easy task, ”Condrond said.

Read the full press release here.

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