A comprehensive 30-year study led by University of California, Irvine glaciologists has produced a circumpolar ice grounding line migration map of Antarctica. An amalgamation of three decades of satellite data compiled and analyzed by the researchers revealed that while most of Antarctica remains remarkably stable, vulnerable sectors are losing grounded ice equivalent to the size of Greater Los Angeles every three years.
The study, published in Proceedings of the National Academy of Sciences, shows that 77 percent of Antarctica’s coastline has experienced no grounding line migration since 1996. However, concentrated retreat in West Antarctica, the Antarctic Peninsula and portions of East Antarctica has resulted in a loss of 12,820 square kilometers (nearly 5,000 square miles) of grounded ice — akin to roughly 10 cities the size of Greater Los Angeles — over the 30-year period.
“The grounding line is where continental ice meets the ocean, and measuring the movement of grounding lines with satellite-based synthetic aperture radar has been our gold standard for documenting ice sheet stability,” said lead author Eric Rignot, UC Irvine distinguished professor and Donald Bren Professor of Earth system science. “We’ve known it’s critically important for 30 years, but this is the first time we’ve mapped it comprehensively across all of Antarctica over such a long time span.”
The ice sheet has been retreating from the grounding line at an average rate of 442 square kilometers per year. The most dramatic changes occurred in West Antarctica’s Amundsen Sea and Getz sectors, where glaciers retreated 10 to about 40 kilometers. Pine Island Glacier retreated 33 kilometers, Thwaites Glacier 26 kilometers, and Smith Glacier an extraordinary 42 kilometers.
“Where warm ocean water is pushed by winds to reach glaciers, that’s where we see the big wounds in Antarctica,” explained Rignot, who’s also a senior research scientist at NASA’s Jet Propulsion Laboratory. “It’s like the balloon that’s not punctured everywhere, but where it is punctured, it’s punctured deep.”
Researchers compiled data from multiple satellite missions, including the European Space Agency’s ERS-1/2 and Sentinel-1, Canada’s RADARSAT 1, RADARSAT 2 and RADARSAT Constellation Mission, Japan’s ALOS/PALSAR and ALOS/PALSAR-2, Italy’s COSMO-SkyMed, the German Aerospace Center’s TerraSAR-X and Argentina’s SAOCOM.
According to co-author Bernd Scheuchl, UC Irvine project scientist in Earth system science, the study represents a landmark achievement for NASA’s Commercial Satellite Data Acquisition program, marking the first major success involving commercial synthetic aperture radar data providers for polar research.
The team benefited from data supplied through NASA CSDA by companies such as Airbus U.S. and Irvine-based ICEYE US. The glaciologists also separately obtained data from Finland’s ICEYE Ltd., with which UC Irvine has had a longstanding collaboration, including a project measuring the rapid deterioration of Antarctica’s Thwaites Glacier.
“This work shows how commercial SAR data can be used to contribute to the virtual SAR constellation by augmenting the program of record from agency-run missions,” Scheuchl said. “The ability to access daily observations in critical areas using commercial assets, combined with decades of international space agency data with large-area coverage, has opened a new era in polar monitoring.”
While researchers can explain most retreat patterns through the intrusion of warm ocean water below ice sheets, significant grounding line migration along the northeast Antarctic Peninsula remains puzzling.
“A lot of these places have warm ocean water in proximity, but on the east coast of the peninsula, there’s substantial retreat, and we don’t have evidence for warm water,” Rignot said. “Something else is acting – it’s still a question mark.”
In this region, multiple ice shelves collapsed prior to the study period, and glaciers including Edgeworth (which lost 16 kilometers), Boydell, Sjogren, Bombardier and Dinsmoor have significantly retreated. The Hektoria, Green and Evans glaciers calved 21 kilometers, 16 kilometers and 9 kilometers, respectively, past their 1996 grounding line positions.
The continental grounding line record provides crucial benchmarks for next-generation ice sheet models tasked with projecting future sea level rise.
“Models have to demonstrate they can match this 30-year record to claim credibility for their projections,” Rignot noted. “That’s the real value of this observational record: knowing that this grounding line migration has happened. If a model can’t reproduce this record, the modeling team will need to go back to the drawing board and figure out what boundary condition or physics are missing.”
The findings also provide essential context for mass balance assessments, the researchers said. The confirmation that 77 percent of Antarctica is highly stable helps reconcile divergent results from different measurement methods in East Antarctica. And the work verifies where mass loss is actively occurring in other parts of Antarctica.
“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.”
The research team included scientists from UC Irvine, NASA JPL, France’s University Grenoble Alpes and the University of Washington in Seattle, as well as collaborators from ICEYE Ltd. in Uusimaa, Finland, and ICEYE U.S. in Irvine. NASA provided funding support.
