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- Jonathan Amos
- science correspondent
image source, NASA/USGS/SPL
America’s Landsat spacecraft has overlooked Antarctica since 1973
Scientists say they now know exactly when and where Antarctica’s edge began melting.
They tracked the changing shape of ridges on the ice surface that indicate where glaciers are anchored.
Half a century ago, few of these frozen moorings, or “pinpoints,” were changing significantly.
But since 2000, more than a third have shrunk in size, highlighting accelerated melting.
The study, published in the journal Nature, reiterates that ice loss from continents will significantly contribute to future sea level rise around the world.
The focus of the study was the ice shelves that border 75% of Antarctica’s coastline.
A shelf is a floating front of a glacier pushed out into the surrounding ocean.
Many of them, especially in the western part of the continent, are under attack by warm water and are thin as a result.
This is bad news because they are considered an important braking mechanism to slow the movement of ice from the continent.
Where the ocean floor is shallow, such as where there are underwater hills, the shelf can get stuck in place and glacier ice can be pushed backwards.
The pinning point is fairly obvious to passing satellites because it produces a lump on the surface of the shelf that the flowing ice had to climb over.
What the team at the University of Edinburgh did was analyze how these bumps changed shape over time.
The surface irregularities above the pinning points may decrease in size or even disappear.
The idea was to see if the bumps got smaller. This means that the shelves are thinning, that is, they are melting. It is said that the braking force has become weaker.
Dr Bertie Miles has traced back the entire image archive of America’s long-running Landsat spacecraft series to assemble a new mosaic of Antarctica’s cloudless coastline.
They then analyzed what happened at the ice surface during three time periods: 1973-1989, 1990-2000, and 2000-2022.
In the initial stage, the pinning point size was reduced by only 15%. It then increased in the 1990s and 25% experienced a contraction. And in the final period, we saw 37% of the pinpoint bumps get smaller.
“As we look at 10-year snapshots, we see that these bumps are getting smaller overall and, in some cases, disappearing completely,” Dr. Miles said.
“What you have to remember is that once an ice shelf loses pinpoint contact, it’s very difficult to regain contact because of the dynamic reactions that occur within the ice. “The grounding line, the line where the glacier is located, changes because it starts to rise, so it’s still touching the ocean floor, but it’s starting to retreat,” he told BBC News.
image source, NASA/USGS/B. Miles/University of Edinburgh
Bertie Miles spent two years lining up Landsat images to construct a new view of the cloud-free coastline.
What’s interesting about this study is that it uses a different approach than how ice shelf thinning is typically assessed.
This is done using a specific type of satellite called an altimeter, which sends out radar pulses to measure the height of the ice surface with great precision.
However, this gold standard technology only dates back 30 years to the early 90s.
By using proxies of ice uplift in Landsat imagery, we can delay the observational record of thinning by an additional 20 years.
Co-author Professor Rob Bingham, from the University of Edinburgh, said this deeper history allowed them to better understand when and where ice loss actually occurred.
“Landsat records show, for example, that the famous large glaciers in West Antarctica, Pine Island and Thwaites, are very unusual in that changes were already occurring in the 1970s,” he explained.
“But in many other places, and in the waters around the Amundsen Sea where thinning is now fully widespread, we didn’t see anything like that happening until the 1990s.”
Professor Helen Fricker of the Scripps Institution of Oceanography in San Diego uses satellite altimetry to observe ice shelves. She praised her research in Edinburgh.
“Floating shelves touch the ice sheet, providing structural support and supporting the ice sheet, much like flying buttresses touch a building.
“Pinpoints increase this effect, and support weakens when contact is lost. So by focusing on pinpoints, this excellent study seeks to understand the stability of Antarctic support and how it And we assessed where it was weakening,” she told BBC News.
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