Thirty years of radar from satellites circling the globe now give scientists the first complete map of Antarctica’s grounding line, the thin boundary where land-based ice begins to float. The picture they uncovered is a mix of stability and retreat: about 77 percent of the continent’s edges have barely budged since 1996, but vulnerable sectors in West Antarctica, along the Antarctic Peninsula, and in parts of East Antarctica are losing grounded ice at a startling pace.
Across the last three decades, those losses add up to roughly 4,942 square miles (12,800 square kilometers) — an area comparable to ten Greater Los Angeleses, or the equivalent of Greater Los Angeles every three years. The findings appear in Proceedings of the National Academy of Sciences.
“Where warm ocean water is pushed by winds to reach glaciers, that’s where we see the big wounds in Antarctica,” said lead author Eric Rignot in a press release. “It’s like the balloon that’s not punctured everywhere, but where it is punctured, it’s punctured deep.”
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A 30-Year Record of Antarctica’s Ice Loss Equal to 10 LAs
The study marks the first time scientists have mapped grounding line movement across the entire Antarctic coastline over such a long stretch of time. Researchers combined radar data from multiple satellite missions to track how the ice sheet’s contact with the ocean has shifted.
On average, grounded ice has retreated by about 162 square miles (442 square kilometers) per year. But the changes are not evenly distributed.
The largest losses occurred in West Antarctica’s Amundsen Sea and Getz sectors. Pine Island Glacier retreated roughly 20.5 miles (33 kilometers) over the study period. Thwaites Glacier pulled back about 16 miles (26 kilometers). Smith Glacier receded an extraordinary 26 miles (42 kilometers).
Elsewhere, particularly along much of East Antarctica, the grounding line has remained largely in place.
Why Some Antarctic Glaciers Are Retreating
In many of the fastest-changing areas, the ocean is doing the work. Winds can push relatively warm water beneath floating ice shelves, thinning them from below. As that support weakens, the grounded ice upstream begins to slide back.
That pattern explains much of what researchers see in West Antarctica, but it does not explain everything.
Along the northeast Antarctic Peninsula, grounding lines have also shifted inland, even though researchers have not found clear signs of warm water reaching the base of those glaciers. Several ice shelves in the region collapsed before this study began, and glaciers such as Edgeworth, Boydell, Sjogren, Bombardier, and Dinsmoor have continued to retreat. Hektoria Glacier alone has moved back more than 12 miles (20 kilometers) since 1996.
Something else may be contributing there. For now, the exact trigger remains unclear.
A Test for Future Sea Level Projections
The value of the new map is not only in showing where change has happened. It also sets a benchmark.
Ice sheet models used to estimate future sea level rise will need to reproduce this 30-year record if they are going to be taken seriously. The observations provide a clear measure of how Antarctica has behaved over a meaningful period.
If a model cannot capture both the stability along much of the coastline and the sharp retreat in vulnerable sectors, researchers will know adjustments are needed.
The long record also helps sort through conflicting measurements of Antarctica’s overall mass balance, especially in East Antarctica. Confirming that most of the coastline has stayed in place helps explain why some studies show relative stability, even as others highlight concentrated losses.
The map ultimately shows a continent that is not changing everywhere at once. Large stretches remain steady.
“The flip side is that we should perhaps feel fortunate that all of Antarctica isn’t reacting right now, because we would be in far more trouble,” Rignot said. “But that could be the next step.”
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- This article references information from a recent study published in the Proceedings of the National Academy of Sciences:
Thirty years of glacier grounding line retreat in Antarctica
