A massive hole the size of Switzerland opened in Antarctica’s sea ice

The mystery of the Maud Rise polynya finally has an answer—and it’s a story that stretches from the seafloor to the sky.

A hole in the ice, hundreds of miles from shore

In the winter of 2017, scientists spotted something strange: a massive hole in the sea ice of Antarctica’s Weddell Sea. About the size of Switzerland, it opened up in the middle of nowhere—far from any coastline—and stayed open for weeks.

This kind of opening is known as a polynya. It wasn’t the first time it had appeared in this region. A similar hole lingered over the same spot—Maud Rise—in the 1970s. But after that, it all but vanished. So when it returned decades later, scientists were determined to figure out why.

How do these holes even form?

Normally, the Southern Ocean is layered like a cake: cold, fresh water on top, and warmer, saltier water below. That layering keeps everything fairly stable.

But for a polynya to form, that structure has to break. Salt needs to mix into the surface, making it heavier. When that happens, warm water from below starts rising, melting the ice from underneath and opening a gap.

This process—called deep ocean convection—releases huge amounts of heat into the air and allows the ocean to “breathe,” releasing gases like carbon dioxide.

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What makes Maud Rise so special?

Maud Rise is an underwater mountain nearly 4,600 feet tall. It disrupts ocean currents and can trap water in spinning loops. Back in the 1970s, this helped keep a polynya open for three winters in a row. Scientists assumed it would become a regular event—but it didn’t.

Then came 2017. Researchers from the University of Southampton, led by Aditya Narayanan, teamed up with oceanographers and climate scientists to figure out what brought it back. They used robotic floats, satellite data, and even tagged elephant seals to gather clues.

A perfect storm of salt, heat, and wind

The team found that during those winters, a giant ocean current called the Weddell Gyre sped up. That spin dragged warmer, saltier water closer to the surface—enough to melt ice from below.

At the same time, a series of powerful storms swept across the Southern Ocean. These winds pushed sea ice outward, dragged salty water toward Maud Rise, and helped churn the ocean’s surface.

Add to that atmospheric rivers—long bands of warm, moist air—and the top layer of ocean lost its usual stability.

Then came the final shove: Ekman transport

The last piece of the puzzle was something called Ekman transport—a concept from early ocean physics. When wind moves across the ocean, the Earth’s rotation pushes the surface water at a right angle to the wind.

That shift funneled even more salt-laden water onto the northern flank of Maud Rise—exactly where the hole opened. With enough salt and heat mixing at the surface, the lid of sea ice couldn’t hold.

By late September, the polynya had released over 20 times the normal heat that escapes from solid sea ice—before it finally froze shut again.

A global story, not just a local one

Even though the Maud Rise polynya formed in a remote part of the Southern Ocean, its effects travel far.

“The imprint of polynyas can stick around in ocean water for years,” said Professor Sarah Gille from UC San Diego. “They can shift ocean circulation, move heat around, and even influence how currents behave near Antarctica.”

The dense, salty water created here can spread across the globe—fueling deep ocean currents that regulate climate and transport carbon and oxygen.

Looking ahead

This polynya might just be one piece of a larger shift. Scientists have noticed that since 2016, sea ice in the Southern Ocean has started to decline—a reversal from the stability seen in previous decades.

“The conditions that brought the polynya back—stronger currents, more storms, more mixing—are all connected to a warming climate,” said Gille.

Whether or not it returns, the 2017 Maud Rise event reminds us that even the most remote parts of the world are deeply tied to our global climate story.

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