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Antarctic ice sheets can retreat as fast 165 feet per day

Antarctic ice sheets can retreat as fast 165 feet per day
Scientists on the Wendell Sea Expedition mapped the seafloor near Antarctica's Larsen C ice shelf. Photo by Julian Dowdeswell

May 28 (UPI) -- Antarctic ice sheets can retreat much faster than modern satellite measurements suggest, new research shows.

According to a survey of ridge patterns along the Antarctica seafloor -- published Thursday in the journal Science -- the continent's ice sheets can retreat upwards of 165 feet per day.

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"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," Julian Dowdeswell, director of the Scott Polar Research Institute at the University of Cambridge, said in a news release.

In 2019, researchers on the Weddell Sea Expedition set out to find Sir Ernest Shackleton's sunken ship Endurance. Sea ice conditions prevented the team from locating the shipwreck, but scientists successfully mapped the seafloor surrounding the Larsen Ice Shelf, which extends off the east coast of the Antarctic Peninsula.

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Because ice shelves like Larsen C act like dams, slowing the flow of inland ice toward the coast, understanding their structural integrity is essential to forecasting the loss of Antarctic ice.

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As previous studies have demonstrated, currents have pushed warm water beneath several of Antarctica's ice sheets, accelerating melt rates and threatening their stability. At the same time, warmer air temperatures are accelerating melt rates from the top.

To better understand what glacial flow rates might look like should Antarctica's dam-like ice sheets collapse, scientists turned the seafloor signatures left by retreating ice sheets 12,000 years ago.

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"By examining landforms on the seafloor, we were able to make determinations about how the ice behaved in the past," said Dowdeswell, who served as chief scientist on the Weddell Sea Expedition. "We knew these features were there, but we've never been able to examine them in such great detail before."

Researchers detected delicate wave-like ridges on the seafloor, marks they determined were left by the influence of the tides on the grounding lines of ancient ice sheets -- the area where the ice sheet begins to float.

By measuring the distance between ridges, formed over the course of a 12-hour tidal cycle, scientists were able to calculate the daily retreat of Antarctica's ice sheets at the end of the Paleolithic ice age.

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As Earth's atmosphere rapidly warmed some 12,000 years ago, Antarctica's ice sheet retreated between 40 and 50 meters, or as much as 165 feet, per day -- more than six miles a year. Today, even Antarctica's fastest glaciers, like those found on Pine Island, are retreating less than a mile per year.

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"The deep marine environment is actually quite quiet offshore of Antarctica, allowing features such as these to be well-preserved through time on the seafloor," said Dowdeswell. "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."

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