Doomsday Glacier: Within 20 years, this ice loss force will activate

Narrowing of the main ice stream, or trunk, could stop ice loss by creating a new balance of forces, whereas widening it might actually make instability worse.

Now, this most recent research makes use of numerical modeling to demonstrate how the eastern and western borders of Thwaites Glacier's main trunk may be impacted by the glacier's quick but uneven thinning.

Paul Summers, a Ph.D. student in geophysics, and his team discovered that Thwaites Glacier's observed thinning, along with changes to its surface's slope and the environment at its base, makes both sides susceptible to moving a few miles outward during the following 20 years.

"We are considering relatively small changes in driving stress as would realistically occur in the coming two decades," Summers and colleagues wrote in a press release. 

They argue that although it only accounts for roughly 2 percent of the glacier's overall width, the slight broadening could hasten its continuous ice loss.

'You monitor the storms as they come in'

"If the widening trend were to continue and were to accelerate, then we'd better know. It would mean that we would have to prepare for higher sea levels," said senior study author Jenny Suckale.

According to Summers, the team expected the glacier's eastern shear margin as most prone to eroding away from the main trunk. Therefore, they were surprised that the western barrier also appears prone to widening in the simulation. 

They claim that this discovery proves how crucial it is to intensify study on the western margin in addition to that already being done on the eastern side. 

"We are very intentionally focusing on the next two decades to enable testability and continued model development," stated Suckale. 

"It's kind of like weather predictions. You monitor the storms as they come in, and then you update your predictions and pass that information on."

"I think we need to monitor Thwaites and make sure we have ways to get that information into planners' hands. "We don't need to hit the panic button, but we also can't ignore this," she concluded.

Study abstract:

Projections of global sea level depend sensitively on whether Thwaites Glacier, Antarctica, will continue to lose ice rapidly. Prior studies have focused primarily on understanding the evolution of ice velocity and whether the reverse-sloping bed at Thwaites Glacier could drive irreversible retreat. However, the overall ice flux to the ocean and the possibility of irreversible retreat depend not only on the ice speed but also on the width of the main ice trunk. Here, we complement prior work by focusing specifically on understanding whether the lateral boundaries of the main ice trunk, termed shear margins, might migrate over time. We hypothesize that the shear margins at Thwaites Glacier will migrate on a decadal timescale in response to continued ice thinning and surface steepening. We test this hypothesis by developing a depth-averaged, thermomechanical free-boundary model that captures the complex topography underneath the glacier and solves for both the ice velocity and for the position of the shear margins. We find that both shear margins are prone to migration in response to ice thinning with basal strength and surface slope steepening determining their relative motion. We construct four end-member cases of basal strength that represent different physical properties governing friction at the glacier bed and present two cases of ice thinning to contrast the effects of surface steepening and ice thinning. We test our model by hindcasting historic data and discuss how data from ongoing field campaigns could further be used to test our model.