Massive ice sheets are capable of shrinking at a rate that is significantly faster than previous thought — 20 times faster, depending on the period of climate warming and the state of the seafloor, according to a new study.
Researchers pored over high-resolution images of the seafloor and found that in the past, a massive ice sheet retreated by up to 600 metres a day during one of the most significant warming periods of Earth’s history.
The study, published last week in the peer-reviewed journal Nature, looked at data pertaining to a former ice sheet that extended out from Norway until it retreated around 20,000 years ago, at the end of the last Ice Age.
“Our research provides a warning from the past about the speeds that ice sheets are physically capable of retreating at,” Christine Batchelor, with Newcastle University, said in a press release. “Our results show that pulses of rapid retreat can be far quicker than anything we’ve seen so far.”
In order to track the path of a long-gone ice sheet, researchers looked at incredibly detailed images of the sea floor which showed more than 7,600 ridges that marked the sheet’s path.
Called “corrugation ridges,” these patterns in the sea floor are less than 2.5 metres in height and can be as close as 25 metres apart or as far as 300 metres. According to scientists, these ridges were formed by the tides as the edge of the ice sheet moved, with each low tide depositing seafloor sediments into a ridge. Since the tide came in and out twice a day in this area, scientists were able to measure how far the ice sheet had retreated in a day by looking at the ridges in pairs of two.
Researchers found that this specific ice sheet, which was more than 30,000 square kilometres in size, had retreated at a speed which ranged from 50 to 600 metres a day.
It’s a rate of ice sheet collapse that is much faster than any ice sheets see from satellites or estimated based on Antarctica land mass changes.
This information helps to inform models which lay out how the globe’s ice sheets could change in future warming events. It’s invaluable to know what degree of warming could cause such a rapid retreat of ice sheets as the planet continues to warm due to human-driven climate change.
The circumstances of this ice sheet’s retreat were far different than today, as this was at the end of an Ice Age. But it still provides insight on how ice sheets are capable of shrinking quite rapidly.
“This shows how rates of ice-sheet retreat averaged over several years or longer can conceal shorter episodes of more rapid retreat,” Julian Dowdeswell, a professor at the Scott Polar Research Institute at the University of Cambridge and study co-author, said in the release. “It is important that computer simulations are able to reproduce this ‘pulsed’ ice-sheet behaviour.”
Looking at images of the seafloor for this study also gave researchers an insight into how the seafloor itself plays a role in ice sheet retreat. Researchers observed that the periods of fastest daily retreat occurred where the seafloor was flattest, meaning the ice sheet would’ve experienced the least amount of challenge to its movement, and could almost just float along.
“An ice margin can unground from the seafloor and retreat near-instantly when it becomes buoyant,” Frazer Christie, a co-author with the Scott Polar Research Institute, said in the release. “This style of retreat only occurs across relatively flat beds, where less melting is required to thin the overlying ice to the point where it starts to float.”
So how likely are we to see ice sheets retreating at this rapid pace in the coming years? According to researchers, it could soon occur in parts of Antartica. One specific glacier in Antarctica, the Thwaites Glacier, has recently pulled back close to a relatively flat area of seafloor.
“Our findings suggest that present-day rates of melting are sufficient to cause short pulses of rapid retreat across flat-bedded areas of the Antarctic Ice Sheet, including at Thwaites,” Batchelor said. “Satellites may well detect this style of ice-sheet retreat in the near-future, especially if we continue our current trend of climate warming.”
