Daily tides bring warm ocean water farther in beneath West Antarctica’s Thwaites Glacier than previously thought, potentially causing ice to melt faster than expected, according to a new study. The finding could help scientists make better predictions about the fate of one of the world’s most closely watched glaciers.
Thwaites, known as the “Doomsday Glacier,” is about the size of Florida. It currently contributes about 4% to global annual sea level rise.
Most ice sheet simulations have not accurately predicted Thwaites’s recent retreat because they assume that a glacier’s grounding line is fixed. But recent research on Thwaites and other glaciers has shown that these boundaries between floating ice and ice that is grounded on the seafloor shift with the daily tide.
“What they could see [were] these really short-timescale processes.”
Glaciers are heavily crevassed above their grounding lines, so studying them from the top of the ice is dangerous. Satellite data can help scientists illuminate the glacier’s underbelly from high above, but most satellites pass over a given spot only once every few days. That’s not enough resolution to work out how tides contribute to the daily movement of the grounding line.
Using satellite radar data from the private company ICEYE collected over 3 months in 2023, a team of glaciologists created a detailed image of Thwaites’s shifting grounding line by looking at how the glacier surface bobbed up and down throughout the day.
“The difference with this study is that they were having multiple measurements per day,” said Alex Brisbourne, a glaciologist at the British Antarctic Survey who was not involved with the research. “So what they could see [were] these really short-timescale processes.”
Satellites can see only the surface of the ice, but because the ice is compacted, tiny vertical movements signal that the glacier bed must be rising too, wrote Eric Rignot in an email. Rignot is a glaciologist at the University of California, Irvine, and NASA’s Jet Propulsion Laboratory and first author of the study.
“Think about spraying an icy road with a jet of salty warm water—you don’t need meters of that salt water to melt ice rapidly.”
The team found that the ice rose and sank in sync with the tides. The data suggested that the grounding line migrated up to 6 kilometers (3.7 miles) inland during an average high tide.
When the tides were particularly high, the glacier’s uplift suggested that a thin layer of seawater up to 10 centimeters (4 inches) deep pushed another 6 kilometers (3.7 miles) inland. The researchers think that this extra water may be causing more melting than current estimates predict because it replaces cold melted fresh water that lines the base of the glacier with warmer, salty seawater.
“Think about spraying an icy road with a jet of salty warm water—you don’t need meters of that salt water to melt ice rapidly,” Rignot wrote.
The study was published in the Proceedings of the National Academy of Sciences of the United States of America.
More Accurate Melting?
Thwaites acts as a natural dam to the land ice in West Antarctica—once Thwaites is gone, those glaciers could more easily flow into the ocean and melt. Rignot and his coauthors think their findings could make future melting predictions more accurate.
Their results showed that seawater affects a larger area under glaciers than previously thought. In ice sheet simulations, this information could help scientists more accurately predict how warming oceans will melt more basal ice, Rignot wrote. If ocean temperatures rise, glaciers may not replace melted ice fast enough, causing them to shrink and contribute more to sea level rise, he explained.
“Timing of this sea level rise is critical,” said Christine Dow, a professor at the University of Waterloo in Canada and a coauthor of the study.“And, in this case, erring on the side of assuming it will happen faster rather than slower is likely the best way forward.”
—Anupama Chandrasekaran (@indiantimbre), Science Writer