Antarctic glaciers are melting much faster than expected

In a group of smaller glaciers, it is mainly the free-floating underside of the ice that detaches. Sea level could rise by up to 1.3 meters.

New bad news from the South Pole: A group of smaller glaciers in western Antarctica – Smith, Pope and Kohler – have been melting faster than previous models suggested for around 30 years. They have thinned, lost ice shelves to the ocean, and retreated further inland. This is the result of a study that has now been published in the journal “Nature Geoscience”.

The researchers tracked down the rapid melting with the help of special radar data from the Tandem-X and Cosmo-Skymed satellite missions. What they noticed in particular was the decline in the so-called touchdown line. This is the limit at which the ice loses contact with the mainland and begins to float on the sea. The radar experts therefore focused their attention on this transition area. For the first time, they were also able to demonstrate drastic changes in the Pope Glacier, which retreated in 2017 within just three months at a rate of 11.7 kilometers per year.

For the analysis, the Institute for High Frequency Technology and Radar Systems at the German Aerospace Center (DLR) worked together with international research partners such as the University of Houston, institutions at the University of California, the Université Grenoble Alpes and the Italian space agency ASI. They consider the knowledge gained to be crucial for better understanding glacial processes and thus predicting the development of the entire Antarctic. In the future, climate researchers will be able to calculate even more precisely how much the sea level will rise and which protective measures are most effective.

So far, the neighboring ice giants Thwaites and Pine Island have been the focus of research because they are very fragile and could cause global sea levels to rise by up to 1.2 meters. The team estimates that the changes in the smaller group will result in an additional increase of around 10 centimeters. Thwaites is already considered a “doomsday glacier”. Just recently, another group of researchers discovered extensive, apparently growing cracks in this Florida-sized ice mass. She fears a chain reaction when the floating tongue tears off.

The underside of a glacier cannot be seen by humans, so that until now the loss of ice was not considered to be directly measurable. However, thanks to digital Tandem-X elevation models, the scientists were now able to determine this hidden melting rate more precisely. Among other things, they found that while Smith Glacier melted over land at about five meters per year between 2011 and 2019, the melting rate on the free-floating underside of the glacier was around 22 meters per year. In certain places, the ice mass even showed melting rates of more than 100 meters per year. The peak value was 140 meters in 2016.

Antarctic glaciers
West Antarctica: TanDEM-X terrain representation of the Kohler, Smith and Pope glaciers

The physical melting processes of Pope, Smith and Kohler were identical for the other glaciers around the Amundsen Sea, the researchers warn. The giants Thwaites and Pine Island could destabilize the rest of West Antarctica with their high mass losses. This would have devastating consequences for life on earth as a whole. The debate about reaching the tipping point of the ice sheet in the region has been going on with renewed intensity for some time. A new temperature record of 18.3 degrees Celsius was also measured in Antarctica in February 2020.

“In order to determine the melt rates, we at DLR also generated more than 240 digital tandem X elevation models, which map West Antarctica from 2011 to 2019 with great precision,” explains co-author Paola Rizzoli from the DLR institute mainly involved. This includes a well-established production chain: The German Space Operations Center is responsible for operating Terrasar-X and Tandem-X and commands the twin satellites for the required recordings.

The radar data is recorded by the German Remote Sensing Data Center at its receiving stations in Neustrelitz, Inuvik (Canadian Arctic) and Gars O’Higgins (Antarctica). The DLR Institute for Remote Sensing Technology supplies the input data for the automated processing of the radar data. The tandem X images are measured using interference technology, geocoded and calibrated at the DLR Institute of Microwave Technology and Radar Systems.

The researchers expect further improvements from future satellite missions: With this, glacier structures and their dynamic processes could be imaged even more precisely in the long-wave frequency range in the radio spectrum from 1 to 2 GHz, the L-band, since it would also be possible to look through vegetation.

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