The largest ice shelf in Antarctica is behaving strangely

Ice current activity caused the Ross Ice Sheet to move suddenly.

In Antarctica, massive glaciers are constantly moving. Ice flows, which act like conveyor belts, are fast-moving pathways that transport most of the ice and sediment remnants from these vast glaciers to the ocean.

According to new research from the University of Washington in St. Louis, one such ice flow dislodges the entire Ross Ice Ridge at least once a day.

The discovery is significant because of the size of the Ross Ice Sheet: it is the largest ice sheet in Antarctica, roughly the size of France.

“We found that the entire shelf suddenly moves about 6 to 8 centimeters (or 3 inches) once or twice a day, triggered by the sliding of an ice stream flowing into the ice shelf,” said Doug Wiens, the Robert S. Brookings Distinguished Professor of Science. earth, environment and planet in art and science. “These sudden movements could potentially play a role in triggering ice earthquakes and breaks in the ice shelf.”

The Ross Ice Shelf is a floating edge of ice that extends across the ocean from inland glaciers.

Scientists are interested in the interactions between ice shelves and ice streams in part because they are concerned about the stability of the Antarctic ice shelves in a warming world.

Ice shelves act as brakes for glaciers and ice streams, slowing their journey to the sea where they melt, allowing more ice to accumulate on the continent. If the ice ridge collapses, that support disappears and the glaciers can flow faster. Once they flow into the ocean, they contribute to sea level rise.

A new study, published in the journal Geophysical Research Lettersfocuses on the movement caused by the Whillans Ice Stream, one of about half a dozen large, fast-moving rivers of ice that flow into the Ross Ice Shelf.

“One wouldn’t detect movement just by feeling,” Wiens said. “The movement occurs over a period of several minutes, so it is not noticeable without instruments. That’s why the movement has not been detected until now, although people have walked and camped on the Ross Ice Shelf since the time of the great explorers Robert F. Scott and Roald Amundsen.”

Sudden sliding

The movement of the Ross Ice Sheet is driven by a relatively sudden — in glacial terms — movement of the ice stream called gliding. This is somewhat similar to the “stick-slip” that occurs along faults before and during an earthquake.

According to the scenario observed by Wiens and his team, a large part of the Whillans ice stream, measuring more than 100 km by 100 km, remains stationary while the rest of the ice stream crawls forward. Then, once or twice a day, much of it swings toward the Ross Ice Shelf.

It can move as much as 40 cm (16 inches) in minutes, Wiens said.

Studies of ice flows over the last 50 years show that some ice flows are speeding up and others are slowing down. Scientists can use seismographs to detect the sudden movement of ice flows to better understand what controls that movement. Wiens and his team traveled to Antarctica in 2014 to set up the seismographs used in this study.

“I’ve published several papers in the past on Whillans Ice Stream gliding events, but until now I hadn’t discovered that the entire Ross Ice Sheet was also moving,” Wiens said.

The researchers do not think these slip events are directly related to human-caused global warming. One theory is that they are caused by the loss of water in the bed of the Whillans Ice Stream, making it “stickier”.

The stress and strains associated with slip events are similar to the stress and strain observed to cause ice earthquakes under different conditions.

“At this point, ice quakes and breaks are just part of the normal life of an ice sheet,” Wiens said. “There is concern that the Ross Ice Shelf will one day break up, as other smaller and thinner ice shelves have done. We also know that the Ross Ice Sheet broke up during the last interglacial period — about 120,000 years ago — and this caused a rapid loss of ice on other glaciers and ice streams that fed into it.”

Reference: “Ross Ice Shelf Displacement and Elastic Plate Waves Induced by Whillans Ice Stream Slip Events” by Douglas A. Wiens, Richard C. Aster, Andrew A. Nyblade, Peter D. Bromirski, Peter Gerstoft and Ralph A. Stephen, 27. March 2024, Geophysical Research Letters.
DOI: 10.1029/2023GL108040