Unraveling the Mystery: Why a Switzerland-Sized Hole Formed in Antarctica’s Sea Ice

In Antarctica, the sea ice typically forms a bright cover over vast areas. However, NASA scientists were surprised when they discovered a large, dark patch for the first time. This unusual area, known as a polynya, unexpectedly grew to the size of Switzerland and remained open for weeks.

Researchers later found that this gap, located above the submerged plateau called Maud Rise, had its unique formation. Normally, the Southern Ocean’s water layers sit in a stable arrangement, with lighter freshwater floating on denser, saltier water. To create a mid-ocean polynya, the lighter layer must collapse, allowing convection to occur. This process fractures the ice cover and allows heat and gases to escape into the atmosphere.

Interestingly, coastal polynyas happen every year due to strong winds pushing ice away from the shore. In contrast, oceanic versions are rare. Historical patterns show that Maud Rise, a tall underwater mountain, may play a crucial role in facilitating polynya formation by affecting current flows and trapping water in tight spirals. Between 1974 and 1976, a larger polynya persisted over Maud Rise during winter, leading scientists to initially believe they would see more frequent occurrences. Yet, since then, such openings have been sporadic and brief.

“The 2017 polynya near Maud Rise was the first significant event of its kind since the 1970s,” said Aditya Narayanan from the University of Southampton. His team used advanced technology, including robotic floats and high-resolution ocean models, to study this phenomenon and track its effects.

During those winters, the clockwise Weddell Gyre accelerated, bringing warm, salty water closer to the ice. This warming typically should have led to ice formation, but the situation became more complex due to mixing processes. According to Fabien Roquet, a professor of Physical Oceanography, the cold ice layer should have prevented mixing, indicating that additional factors were at play.

Strong extratropical storms contributed to this mix by pushing ice away and bringing salty water toward Maud Rise. Moreover, atmospheric rivers, which are long plumes of rich moisture, helped warm the surface, breaking down the stable layers of water.

Another factor involves a concept called Ekman transport, where wind patterns cause ocean surface currents to shift direction. Roberto Naveira Garabato, another University of Southampton researcher, noted that this process steered salt-rich water toward the area’s northern flank, right where the 2017 polynya appeared. “It was the missing link needed to sustain the vital mixing between salt and heat,” he stated.

These polynyas, while seeming local, can also have worldwide implications. Sarah Gille, professor at the University of California, San Diego, pointed out that their effects can linger for years, influencing ocean currents and global temperatures. When dense water forms in the polynya, it can carry carbon to the surface, affecting atmospheric CO₂ and oceanic life.

As the climate continues to warm, researchers are concerned about these phenomena becoming more common. Since 2016, sea ice levels in the Southern Ocean have been declining, defying previous stability trends observed since the 1970s. If this continues, we may see more surprises of our planet’s polar regions, where changes can have far-reaching effects globally.

This study highlights the unexpected dynamics of Earth’s climate system and reminds us how much we still have to learn about our planet’s processes.

The research was published in the journal Science Advances.

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