Oceanographer Anna Wåhlin paced across the bridge of the Nathaniel B. Palmer icebreaker like a nervous parent waiting for a teenager out past curfew.

The fiery orange submarine, which she named Ran after the Norse goddess of the sea, hadn’t yet resurfaced from its first mission in the watery depths around the face of West Antarctica’s Thwaites Glacier.

“She’s a very temperamental lady,” Wåhlin said of the $3.6 million, unmanned submarine, while peering through her binoculars on an overcast March day.

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Ran was late. Wåhlin wasn’t worried about the submarine disappearing, but this was Ran’s first season in polar waters, and there were a bunch of kinks to work out.

Wåhlin, an oceanographer at Sweden’s University of Gothenburg, was one of the roughly two dozen scientists on a pioneering scientific expedition to Thwaites Glacier this past winter. The two-month cruise aboard the Palmer was the beginning of a five-year, $50 million international collaboration to better understand the plight of Thwaites. Scientists believe the massive glacier is teetering on the brink of collapse, though just how fast that could happen remains an open question.

Florida-sized Thwaites Glacier holds enough ice to raise global sea levels by two feet. If the glacier collapses, it could destabilize a portion of West Antarctica that would, in turn, raise sea levels by about 11 feet.

Oceanographer Anna Wåhlin, director of the Hugin project, waits on the bridge of the Nathaniel B. Palmer for the Hugin submarine to surface in icy seas near the face of Thwaites Glacier. Carolyn Beeler/The World

That would spell disaster for coastal cities from Miami to Mumbai, which would be inundated by floods.

Ground zero for this slow-moving catastrophe is the glacier’s edge, where land-based ice juts out into the Amundsen Sea. Warm water is thought to be melting the underside of this roughly 75-mile ice shelf, but the area is as mysterious as it is consequential.

“We know more about the moon than this particular part of Earth,” Wåhlin said.

Scientists think changing wind patterns are pushing a mass of middepth warm water, called circumpolar deepwater, up from the deep ocean and onto the continental shelf in front of Antarctica and toward Thwaites. But no scientific instrument has ever been underneath the ice shelf to study it.