A team of scientists has learned that the ground beneath West Antarctica’s most vulnerable glaciers is weirdly bouncy. The finding suggests this critical sector of the ice sheet might have a hidden defense against runaway collapse, but how much that helps us depends on if we take action to rein in climate change.
The results, published Thursday in Science, concern the Amundsen Sea Embayment, which is basically the Kanye West of Antarctic ice: impossible to look away from and seemingly on the verge of a catastrophic meltdown.
The Amundsen Sea Embayment is home to Pine Island and Thwaites glaciers, two of the fastest-melting glaciers on the planet. Their grounding lines (the points of contact between ice and rock) are retreating as warm ocean water eats away at the ice and causes it to pop up, creating floating shelves which eventually break apart. And thanks to a quirk of geology—the bedrock gets deeper the further inland you go—grounding line retreat results in progressively thicker ice shelves that are more exposed to warm ocean water.
This situation has led some scientists to warn of a runaway collapse scenario that could raise global sea levels several feet. But there’s a countervailing force that might help reduce the risk of an ice apocalypse: the Earth itself.
Our planet is a deformable ball, and when you remove heavy weight (like a glacier), that ball starts to rebound. The new paper, led by Valentina Barletta at the Technical University of Denmark, aimed to answer how quickly the rebound is occurring by looking at several years of data collected by six GPS sensors placed across the region by co-author Terry Wilson and others.
“Terry Wilson and colleagues were extremely wise and lucky,” Barletta told Earther. “They had really, really good idea [to place those sensors] with very few indication[s] that there might have been something special.”
The GPS data published today shows that the land beneath the Amundsen Sea Embayment is rising at a rate of 41 millimeters (about 2 inches) per year. That’s one of the fastest rates of rebound ever recorded anywhere on the planet. It’s also way higher than most estimates of continent-wide uplift.
“It’s amazing,” Robin Bell, a glaciologist at Columbia University who wasn’t involved with the paper, told Earther.
Using models, Barletta showed that the Amundsen Sea Embayment’s springy step is the result of a relatively low viscosity (or fluid) mantle, one that responds more quickly to changes in the overlying ice, bouncing upward on timescales of decades to centuries instead of millennia. Matt King, an Antarctic researcher at the University of Tasmania, likened the Earth to memory foam. “This study shows this region of Antarctica has a very short memory,” he told Earther.
That has implications both for basic science and our planet’s future.
On the basic science side, the insight will help researchers reduce uncertainty in their measurements of ice loss and reconcile differences between different tools used to make those measurements.
One of our key tools for assessing ice loss is gravity data collected by NASA’s GRACE (and now GRACE-Follow On) satellite mission. The ice has a massive gravitational signature, and as it melts away, that signature diminishes. But bedrock uplift represents new mass coming into the region. Accounting for this, the new study determined that gravity measurements have been underestimating regional ice loss by about 10 percent.
More importantly for coastal dwellers, the finding points to processes that may counteract some of the retreat the ice sheet is expected to see as global temperatures rise. As the ice melts, rapid uplift, along with reduced gravitational attraction between a lighter ice sheet and the ocean, should cause ice streams to partially lift out of the water that’s melting them. This could potentially slow their retreat.
How much these mechanical forces work to counteract ice retreat in West Antarctica is still a big TBD. If the climate warms too quickly, the answer may be very little. But it’s something modelers can now think about.
University of Washington glaciologist Peter Neff told Earther that people who aren’t directly involved in studying the geology of Antarctica tend to write it off.
“But if we don’t understand that it’s a volcanic system and it’s got this weak structure that affects its viscosity, we won’t be able to correctly anticipate what it’s going to do,” he said.
The data may not offer final answers about West Antarctica’s future, but it was hard won, a fact that every researcher I spoke with pointed out. In order to get an accurate picture of rebound, the researchers had to place GPS sensors on bare rock rather than ice (not easy to find in Antarctica) and they had to take measurements year round (not easy to do in Antarctica).
Barletta said looking at pictures of those little sensors out on the ice was the most emotionally poignant part of the research.
“Some of these stations are three, four, five years old,” she said. “Imagine in 20 years: we could have such a long record of ice and Earth monitoring just by this little thing. And that information will be so precious.”