The largest ice shelf in Antarctica is behaving strangely

Research from Washington University in St. Louis reveals that the Ross Ice Shelf in Antarctica, roughly the size of France, is being displaced daily by the ice stream. This movement caused by sudden slip in the ice stream could affect ice shocks and shelf breaks, raising concerns about the stability of ice shelves in a warming world.

The activity of the ice stream caused the Ross Ice Shelf to shift suddenly.

In Antarctica, massive glaciers are constantly moving. Acting as conveyor belts, ice streams are pathways of accelerated movement that transport most of the ice and sediment debris from these vast glaciers toward the ocean.

According to new research from Washington University in St. Louis one such ice stream at least once a day pushes the entire Ross Ice Shelf out of place.

The finding is significant because of the size of the Ross Ice Shelf: It is the largest ice shelf in Antarctica, about the size of France.

“We found that the entire shelf suddenly moves 6 to 8 centimeters (or 3 inches) once or twice a day, which is caused by slippage of ice flowing into the ice shelf,” said Doug Wiens, Robert S. Brookings. Distinguished Professor of Earth, Environmental, and Planetary Sciences in Arts and Sciences. “These sudden movements could potentially play a role in triggering ice shocks and breaks in the ice shelf.”

The Ross Ice Shelf is a floating ice shelf that extends over the ocean from inland glaciers.

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

Ice shelves act as brakes for glaciers and ice streams, slowing their journey into the sea where they melt, allowing more ice to accumulate on the continent. If the ice shelf collapses, this support disappears and the glaciers are free to 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 draining into the Ross Ice Shelf.

“One would not detect the movement just by feeling,” Wiens said. “The movement occurs over a period of several minutes, so it is not perceptible without instruments. That is why the movement has not yet been detected, even though people have walked and camped on the Ross Ice Shelf since the days of the great explorers Robert F. Scott and Roald Amundsen.”

A sudden slip

The movement of the Ross Ice Shelf is caused by a relatively sudden – in glacial terms – movement of the ice stream called a slip. It is somewhat similar to the “stick-slip” that occurs along a fault before and during an earthquake.

In the scenario Wiens and his team observed, a large section of the Whillans Ice Stream, measuring more than 100 km by 100 km, remains stationary while the rest of the ice stream creeps forward. Then, once or twice a day, a large section rushes forward against the Ross Ice Shelf.

It can move up to 40 cm (16 inches) in a few minutes, Wiens said.

Studies of ice streams over the past 50 years show that some ice streams are speeding up, others are slowing down. Scientists can use seismographs to detect the sudden movement of ice streams to help understand what drives this movement. Wiens and his team traveled to Antarctica in 2014 to place the seismographs used in this study.

“I’ve published several articles in the past about Whillans Ice Stream sliding events, but I hadn’t yet found that the entire Ross Ice Shelf was also moving,” Wiens said.

Scientists do not think these slides 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 strain associated with slip events are similar to the stress and strain observed in icequake triggering under different conditions.

“At this point, ice shocks and breaks are just part of the normal life of an ice shelf,” 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 Shelf broke up during the last interglacial period – about 120,000 years ago – and this caused a rapid loss of ice for the 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