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May 30, 2020

Wave-like seafloor ridges reveal rapid retreat of Antarctic ice 12,000 years ago

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P
Pa
May 30, 2020

A team of researchers, which included experts from the universities of Cambridge and Loughborough, analysed the ancient wave-like ridges on the Antarctic seafloor thought to have formed during the last Ice Age around 12,000 years ago.

They found that Antarctic ice surrounding the coastline retreated as much as 40 to 50 metres per day during this period, equivalent to more than 10 kilometres per year.

In comparison, the researchers said, the fastest-retreating grounding lines — places where ice sheets no longer rest directly on the sea floor and begin to float — in Antarctica are currently about 1.6 kilometres per year.

Lead author Professor Julian Dowdeswell, director of the Scott Polar Research Institute at the University of Cambridge, said: “By examining the past footprint of the ice sheet and looking at sets of ridges on the seafloor, we were able to obtain new evidence on maximum past ice retreat rates, which are very much faster than those observed in even the most sensitive parts of Antarctica today.”

An autonomous underwater vehicle was used map the seafloor and measure the delicate ridges in the soft seafloor sediment on the Larsen continental shelf, off the east coast of the Antarctic Peninsula. These wave-like structures, each about one metre high and spaced 20 to 25 metres apart, were thought to have been left behind by retreating ice nearly 12,000 years ago.

The scientists believe these small ridges were caused by the movement of the ice with the tides, “squeezing the sediment into well-preserved geological patterns”, resembling “the rungs of a ladder”.

Prof Dowdeswell said: “By examining landforms on the seafloor, we were able to make determinations about how the ice behaved in the past. We knew these features were there, but we’ve never been able to examine them in such great detail before.”

The scientists say their findings provide an indication of how quickly massive ice sheets can retreat, which if repeated, which would have implications for modern-day sea-level rise.

Prof Dowdeswell said: “We now know that the ice is capable of retreating at speeds far higher than what we see today. Should climate change continue to weaken the ice shelves in the coming decades, we could see similar rates of retreat, with profound implications for global sea level rise.” The results are reported in the journal Science.