Ice sheets can retreat 600 meters per day | Polarjournal
A Landsat-8 image of Thwaites Glacier. It is one of the largest contributors to global sea level rise. Photo: NASA/USGS

Marks in the seafloor dating from the last ice age show that ice sheets can retreat up to 600 meters per day during a warming climate, according to a new study. Thwaites Glacier in Antarctica could face such a scenario, which would significantly accelerate sea level rise. The international research team said in its study that the discovery was a “warning from the past” for the world today.

The scientists mapped more than 7,600 landforms on the seafloor, called “corrugation ridges,” north of Norway over an area of 30,000 square kilometers left behind by a long-gone ice sheet.

The retreating edge of the glacial ice sheet is thought to have left these particular landforms in the seafloor. The ice sheet moved up and down with the tides, its margin pushing sea floor sediments into a ridge at each low tide. With two tidal cycles per day, two corrugation ridges were created each day and the researchers were able to calculate how fast the ice sheet was retreating.

With a distance of 25 to 300 meters between the ridges, this results in retreat rates of the glacial ice sheet of 50 to 600 meters per day, which occurred in pulses. This is a retreat rate 20 times faster than the highest ever measured. The researchers published their findings in the journal Nature.

“Our research provides a warning from the past about the speeds that ice sheets are physically capable of retreating at. Our results show that pulses of rapid retreat can be far quicker than anything we’ve seen so far.”

Dr. Christine Batchelor of the University of Newcastle, principal investigator and lead author of the study.

The new findings are important information for computer models that predict future changes in ice sheets and sea level.

According to the authors, the results suggest that such rapid retreat occurs in phases that last only short periods of time (days to months). “These pulses translate into sea level rise and could be really important for sea defences,” Dr. Batchelor told The Guardian. The rate of loss was critical if, for example, an increase expected over 200 years could actually occur in 20 years, Batchelor added.

High-resolution images from the seafloor reveal the wave pattern caused by the former ice sheet off Norway. Photo: Kartverket

The research team also found that the former ice sheet retreated most rapidly where it rested on a nearly flat seafloor. “An ice margin can unground from the seafloor and retreat near-instantly when it becomes buoyant,” explains Dr. Frazer Christie of the Scott Polar Research Institute, co-author of the study. “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.”

The new results lead the research team to conclude that a similar rapid retreat could soon be observed in certain regions of Antarctica. In particular, Thwaites Glacier in West Antarctica may experience a rapid retreat pulse as its edge has recently approached a flat-bedded area.

“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,” says 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.”

Julia Hager, PolarJournal

Link to the study: Christine L. Batchelor, Frazer D. W. Christie, Dag Ottesen, Aleksandr Montelli, Jeffrey Evans, Evelyn K. Dowdeswell, Lilja R. Bjarnadóttir, Julian A. Dowdeswell. Rapid, buoyancy-driven ice-sheet retreat of hundreds of meters per day. Nature, 2023; DOI: 10.1038/s41586-023-05876-1.

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