Antarctic ice melts from the top down and the bottom up. Researchers and art historians recently digitized an archive of 1970s radar film that peers through the ice surface into the shapes below. The vintage measurements will let glaciologists and climate scientists track changes to the ice across double the time frame offered by modern radar data alone and will aid glacial melt projections.
“A lot of the changes in Antarctica are happening at the bottom,” said Dustin Schroeder, a radar glaciologist at Stanford University in California who led the digitization project. “In the past, we were limited to 1 or 2 decades of modern digital data. But now we have this older record that can extend that back to 40 or 50 years,” he told Eos. “And that time will just grow.”
Peering Through the Ice
Radar sounding is “the geophysical method we use to map what the topography of the continent looks like under the ice sheet,” Schroeder explained. “You send a radar pulse straight down from an airplane, and you look through the ice down to the bed…like a slice of layer cake.”
The technique was groundbreaking for Antarctic research in the 1970s because “we didn’t know what the continent looked like at all,” Schroeder said. From 1971 to 1979, an international survey team flew a 400,000-kilometer zig-zagging path across Antarctica, mapping beneath the ice and storing the radar profiles on 35-millimeter optical film. Much of that film had never been analyzed in detail.
Schroeder’s team worked with art historians and Hollywood vintage film experts to digitize those film reels and archive them online for easy access. The team then combined those older radar profiles with modern radar and altimetry data to measure how the bottom of the Antarctic ice sheet has changed in the past 40–50 years.
With the longer radar timescale, the researchers found that the eastern ice shelf of Thwaites Glacier in West Antarctica has thinned faster than suggested by only 1 decade of data. The ice shelf lost 10%–33% of its thickness between 1978 and 2009 at a rate of about 40 meters per decade, higher than the 25-meter-per-decade rate suggested from modern data alone.
Another subglacial feature, a basal channel beneath the Filchner-Ronne Ice Shelf, remained relatively stable over about 40 years. That at least one feature remained unchanged after including the vintage radar demonstrated that the changes his team saw near Thwaites are real, Schroeder explained. These results were published on 3 September in Proceedings of the National Academy of Sciences of the United States of America.
Learn from the Past to Model the Future
“Digitizing these old radar lines was a real service to the community,” Leigh Stearns told Eos. Stearns is a glaciologist at the University of Kansas in Lawrence and was not involved with this study. “Being able to extend our record of observations, particularly of key variables such as ice thickness and basal condition, provides context for current ice sheet dynamics and helps parameterize ice sheet models,” she said.
The digitization project is a “Herculean effort,” according to Joseph MacGregor, a project scientist for NASA’s Operation IceBridge. “Operation IceBridge’s plans for its final Antarctic campaign this fall include potential repeats of these pioneering missions across the coastline of East Antarctica,” he told Eos. “Repeating these flights gives us a chance to measure any ice thickness change over 4 decades.”
Importantly, the vintage radar film covers some of the most dynamic places in Antarctica, Schroeder said. “The Ross Ice Shelf is one of the densest areas covered by this old survey,” he said. “I think in terms of luck, or prescience, we have film in some of the places we’d most want it.”
You can learn more about the radar digitization project in the video below.
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer
This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.