World news – The ICESat-2 satellite shows the shape and depth of the ice shelf fractures in Antarctica


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March 4, 2021

from Francisco Tutella, Pennsylvania State University

When a block of ice the size of Houston, Texas broke off the Amery Ice Shelf in East Antarctica in 2019, scientists expected the calving event, but not exactly where it would happen. Using satellite data, scientists can now measure the depth and shape of ice shelf fractures to better predict when and where calving events will occur, the researchers said.

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Ice shelves make up nearly 75% of the Antarctic coast and support – or hold back – the larger glaciers on land, said Shujie Wang, assistant professor of geography at Penn State. If the ice shelves collapse and Antarctica’s glaciers fall or melt into the ocean, sea levels would rise up to 200 feet.

« When we try to predict the future contribution of Antarctica to sea level rise, the greatest uncertainty is the stability of the ice shelf, « said Wang, who also has an appointment at the Institute for Earth and Environmental Systems. « There is no easy way to map the depth of fractures in the field on a regional scale. We have found that satellite data captures the depth and surface morphology of ice shelf fractures, allowing us to consistently monitor this information over a large area. »

Between October 2018 and November 2019, Wang and her colleagues examined high-resolution data collected by the Ice, Cloud and Land Uplift Satellite (ICESat-2) over the Amery Ice Shelf, which is about the size of West Virginia. The satellite shoots green laser pulses to the land surface and uses reflected photons to determine the surface elevation. While other satellites have a resolution of several thousand feet, ICESat-2 has a resolution of approximately 56 feet, which allows smaller fractures and fracture morphology to be detected.

The researchers then passed the ICESat-2 data through an algorithm of the surface pit features to locate and characterize fractures in the ice. They reported their results in the journal Remote Sensing of Environment.

The researchers identified three types of fractures – U-shaped, parabolic, and V-shaped fractures – to a depth of 30 meters in the ice shelf. They also realized that this surface information provides insight into what is happening hundreds of feet below the surface of the ice.

The morphology of the basal fractures – the shape and size of the fractures at the base of the ice shelf – is proportional to the surface depressions, according to Wang . As the glacier supported by the ice sheet accumulates more snow and ice, the parabolic-shaped fractures flow to the edges of the ice shelf. Once they cross a certain limit, these surface fractures have greater potential to penetrate deeper into the ice as the basal fractures extend upward. These fractures can then become V-shaped, possibly indicating that a crack has formed – a fracture that penetrates the entire thickness of the ice sheet. These cracks are more likely to cause calving events. « By incorporating satellite-based vertical information, future ice shelf models can be improved, » said Wang. « It can help us predict calving fronts and determine where an ice shelf is susceptible to these events. »

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