Scientists find that during periods of global warming, ice caps can retreat at a rate of up to 600 meters per day, which is 20 times faster than the highest rate of retreat recorded previously.

An international team of scientists, led by Dr Christine Batchelor from the University of Newcastle in the UK, have used high-resolution images of the ocean floor to uncover the rapid rate at which an ancient ice cap that stretched from Norway retreated at the end of the last Ice Age, about 20,000 years ago.

The team, which also included researchers from the universities of Cambridge and Loughborough in the UK and the Geological Survey of Norway, mapped more than 7,600 small-scale landforms called “corrugation ridges” on the seabed. The ridges are less than 2.5 m high and are spaced about 25 to 300 meters apart.

These landforms are understood to have formed when the ice sheet retreat margin moved up and down with the tides, pushing the seafloor sediments into a ridge with each low tide. Since two ridges would have been produced each day (under two tidal cycles per day), the researchers were able to calculate the rate at which the ice sheet retreated.

Example of wavy ridges on the seabed of middle Norway. Two ridges were produced each day by the tidal induced vertical motion of the retreating ice sheet margin. Detailed bathymetric data. 1 credit

Their findings, reported in the journal Natureshow that the ancient ice sheet underwent rapid pulses of retreat at a rate of 50 to 600 meters per day.

This is much faster than any rate of ice sheet retreat that has been observed from satellites or inferred from similar landforms in Antarctica.

“Our research provides a warning from the past about the speeds at which ice sheets are physically capable of retreating,” Dr Batchelor said. “Our results show that rapid retreat impulses can be much faster than anything we’ve seen so far.”

Information about how ice sheets have behaved during past periods of global warming is important to inform computer simulations that predict future ice sheet and sea level changes.

Composite of Sentinel-1 images illustrating the highly fractured, fast-flowing frontal margin of the Thwaites and Crosson Ice Shelves. Credit: Copernicus EU/ESA, processed by Dr Frazer Christie, Scott Polar Research Institute, University of Cambridge

“This study shows the value of acquiring high-resolution images of glacial landscapes that are preserved on the seabed,” said study co-author Dr Dag Ottesen of the Geological Survey of Norway, who participates in the MAREANO seabed mapping program which collects the data.

The new research suggests that periods of such rapid ice sheet retreat can only last for short periods (days to months).

“This shows how rates of ice sheet retreat averaged over several years or more can mask shorter episodes of faster retreat,” said study co-author Professor Julian Dowdeswell of Scott Polar Research. Institute of the University of Cambridge. “It is important that computer simulations are able to reproduce this ‘pulsating’ behavior of the ice sheet.”

Seabed landforms also shed light on the mechanism by which such rapid retreat can occur. Dr. Batchelor and his colleagues noted that the ancient ice sheet retreated fastest on the flattest parts of its bed.

Landsat 8 image showing the heavily crevassed front of the Thwaites Glacier, West Antarctica, and offshore icebergs and pack ice. Credit: NASA/USGS, processed by Dr. Frazer Christie, Scott Polar Research Institute, University of Cambridge.

“A margin of ice can break off the seabed and retreat almost instantly when it becomes buoyant,” explained co-author Dr Frazer Christie, also of the Scott Polar Research Institute. “This style of retreat only occurs on relatively flat beds, where less melting is required to thin the overlying ice to the point where it begins to float.”

The researchers conclude that such rapid retreat pulses may soon be seen in parts of Antarctica. This includes the vast expanses of West Antarctica

” data-gt-translate-attributes=”[{” attribute=””>Thwaites Glacier, which is the subject of considerable international research due to its potential susceptibility to unstable retreat. The authors of this new study suggest that Thwaites Glacier could undergo a pulse of rapid retreat because it has recently retreated close to a flat area of its bed.

“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”, said Dr. Batchelor. “Satellites may well detect this style of ice-sheet retreat in the near future, especially if we continue our current trend of climate warming.”

Reference: “Rapid, buoyancy-driven ice-sheet retreat of hundreds of metres per day” by Christine L. Batchelor, Frazer D. W. Christie, Dag Ottesen, Aleksandr Montelli, Jeffrey Evans, Evelyn K. Dowdeswell, Lilja R. Bjarnadóttir, and Julian A. Dowdeswell, 5 April 2023, Nature.
DOI: 10.1038/s41586-023-05876-1

Other co-authors are Dr. Aleksandr Montelli and Evelyn Dowdeswell at the Scott Polar Research Institute of the University of Cambridge, Dr. Jeffrey Evans at Loughborough University, and Dr. Lilja Bjarnadóttir at the Geological Survey of Norway. The study was supported by the Faculty of Humanities and Social Sciences at Newcastle University, Peterhouse College at the University of Cambridge, the Prince Albert II of Monaco Foundation, and the Geological Survey of Norway.