West Antarctica’s Pine Island glacier is speeding up as its ice shelf disintegrates, new research shows.
By Sarah Kaplan
June 11, 2021
The Pine Island glacier was already scary. The 160-mile-long river of ice is known as “the weak underbelly” of West Antarctica. It contributes more to sea level rise than any other glacier on the continent and ranks among the fastest melting glaciers in the world.
Unlike other Antarctic glaciers, Pine Island is not sheltered from the warming ocean by a vast expanse of sea ice. The only thing preventing it from flowing directly into the Amundsen Sea embayment is a shelf of floating ice that sticks out from the glacier’s edge. This shelf is like a cork in a bottle, pressing against the stable sides of the bay to contain the tremendous pressure at its back.
But the ice shelf is tearing itself apart. It has lost one-fifth of its mass in the last five years, shedding icebergs the size of cities. Rifts have opened up in the center of the shelf, potentially adding to the instability.
Now the world has a whole new reason to worry about Pine Island. According to research published Friday in the journal Science Advances, the glacier is flowing toward the ocean 12 percent faster than at the start of 2017 — a result of the weakened ice shelf’s inability to act like plug.
If this disintegration continues, “the whole shelf could potentially fall apart in the next few years, which is greatly faster than what we expected,” said Ian Joughin, a glaciologist at the University of Washington’s Applied Physics Laboratory who co-wrote the new report.
The loss of the ice shelf would accelerate Pine Island’s decline even further. The faster it flows, the more ice it spits into the ocean, raising sea levels. The glacier already adds a sixth of a millimeter to sea level rise each year; but losing the ice shelf could double or triple that rate, Joughin said. Pine Island contains roughly 180 trillion tons of ice — enough to cause 1.6 feet of sea level rise.
“I’m not really a catastrophist,” Joughin said. “But the integrity of the ice shelf is definitely in question.”
Previously, scientists had focused on the slow but steady thinning of the ice shelf as warm ocean waters seep underneath it. This melting makes ice shelves more vulnerable to collapse during the Antarctic summer, when high temperatures cause melting on the surface. But, since temperatures in West Antarctica are rarely more than a few degrees above freezing, that process was expected to take centuries to unfold.
What’s happening now is much faster and less predictable, Joughin said. It appears that the rapid slide of the glacier is creating fractures in the ice shelf, which leads to more pieces breaking off, or “calving.” Computer simulations and mathematical models support the idea that this process is responsible for the glacier’s speed up.
Pine Island’s ice shelf used to calve every four to six years, according to NASA, but since 2017 it has lost huge chunks of ice every year. Radar instruments on board the European Space Agency’s Sentinel-1 satellites capture images of the glacier every six days, even amid the months-long darkness of Antarctic winter. This allows scientists to watch the ice shelf break up in almost real time.
NASA scientists flew over one of Pine Island’s newly formed bergs in 2018. Even from 1,500 feet, the Seattle-sized fragment took up the researcher’s entire field of vision. “It was spectacular and inspiring and humbling at the same time,” Brooke Medley, deputy project scientist for Operation Ice Bridge, said in a blog post from the agency.
Just two years later, more bergs broke off along the ice shelf’s “shear margin,” where it attaches to thicker ice along the sides of the bay.
It’s as if the cork in the bottle containing Pine Island glacier is crumbling. Having lost contact with the sides of the bay, the shelf is giving way to the river of ice behind it.
Something similar happened in the 1990s and early 2000s to glaciers in the Antarctic Peninsula — the tail-shaped part of the continent that extends toward South America. There, warm temperatures caused the catastrophic breakup of ice shelves over the course of just a few years. Two decades later, the peninsula’s glaciers are still flowing at two or three times their previous rate, contributing to sea level rise.
“The observation of this process [at Pine Island glacier] is new and concerning,” said Bethan Davies, a glaciologist at Royal Holloway University of London who was not involved in the new study.
Pine Island and other West Antarctic glaciers are much bigger than the ones that flow out of the Antarctic peninsula, she noted, making the consequences of retreat far more extreme.
“Ice loss here could be catastrophic and irreversible on centennial time scales,” Davies said.
Joughin’s models can’t say what will happen next. He and his colleagues haven’t observed melt ponds forming on the surface of the ice shelf — something that is known to make ice less stable. The rifting of the ice appeared to slow down in 2020.
On the other hand, if the acceleration of the glacier continues to create fractures, it could lead to a feedback loop that sends the ice shelf into a spiral of decline.
“It’s not at all inconceivable to say the rest of the ice shelf could be gone in a decade,” Joughin said. “It’s a long shot. But it’s not that big a long shot.”
But if ice shelves can shift quickly and decisively, so too can humanity. Healing the ozone hole and taking swift action against climate change will alter the conditions in Antarctica’s atmosphere and oceans and help stabilize the continent’s glaciers.
“The future is still open to change,” Davies said — if people do what is needed to change it.