June 3, 2023

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20 times faster – slabs of ice can collapse much faster than previously thought

Landsat 8 image depicting the ice shelf in the highly dynamic SCAR Inlet, the Antarctic Peninsula, and offshore sea ice production. Credit: NASA/USGS, processed by Dr Fraser Christie, Scott Polar Research Institute, University of Cambridge

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

An international team of scientists, headed by Dr Christine Batchelor of the University of Newcastle in the UK, used high-resolution images of the ocean floor to reveal the rapid pace at which the former ice sheet extending from Norway receded at the end of the war. The last ice age, approximately 20,000 years ago.

The team, which also included researchers from Cambridge and Loughborough Universities in the United Kingdom and the Geological Survey in Norway, mapped more than 7,600 micro-scale terrain called ‘ripple edges’ across the seafloor. The ridges are less than 2.5 meters high and spaced between 25 and 300 metres.

It is understood that this topography was formed when the receding margins of ice sheets moved up and down with the tide, pushing seafloor sediments to the edge at each low tide. Given that two tides would have been produced each day (less than two tidal cycles per day), the researchers were able to calculate how quickly the ice sheet was retreating.

An example of corrugation bridges on the sea floor in Mid-Norway

An example of undulating hills on the sea floor in the middle of Norway. Two ridges were produced each day by the tidal-induced vertical motion of the retreating ice sheet margin. Detailed bathymetry data. Credit: Cartfire.com

Their results have been published in the journal naturethe former ice sheet was shown to undergo pulses of rapid retreat at a speed of 50 to 600 meters per day.

This is much faster than any rate of ice sheet retreat observed from satellites or inferred from similar Antarctic landforms.

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

Information about how ice sheets behaved during past periods of warming climate is important to inform computer simulations that predict future ice cover and sea level change.

Iceberg plant in West Antarctica

Sentinel-1 image composite depicting the highly refracted, fast-flowing anterior margin of the Thwaites and Crowson ice shelves. Credit: EU/ESA Copernicus, Processed by Dr. Fraser Christie, Scott Polar Research Institute, University of Cambridge

“This study shows the value of obtaining high-resolution images about preserved glacial landscapes on the seafloor,” said study co-author Dr Dag Ottesen of the Geological Survey of Norway, who is involved in the MAREANO seafloor mapping programme. Data collected.

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

“This shows how rates of retreat of the average ice sheet over several years or more can mask shorter periods of rapid retreat,” said Professor Julian Dodswell of the Scott Polar Research Institute at the University of Cambridge. “It is important that computer simulations be able to reproduce this ‘pulsating’ behavior of the ice sheets.”

The geomorphology of the seafloor also sheds light on the mechanism by which such rapid decline could occur. Dr. Batchelor and his colleagues noticed that the former ice sheet retreated faster through the flat parts of its bottom.

The severely cleft front of Thwaites Glacier, West Antarctica, icebergs and sea ice offshore

This Landsat 8 image shows the severely rifted front of the Thwaites Glacier, West Antarctica, and icebergs and sea ice offshore. Credit: NASA/USGS, processed by Dr Fraser Christie, Scott Polar Research Institute, University of Cambridge.

The co-author, Dr. “This pattern of retreat only occurs across relatively flat layers, where less melting is required to reduce the overlying ice to the point at which it begins to float.”

The researchers concluded that pulses of similar rapid decline could soon be observed in parts of Antarctica. This includes the vast West Antarctica[{” 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.

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