In 2017, a massive hole reappeared in Antarctica’s winter sea ice above Maud Rise, baffling scientists. This rare opening, called a polynya, hadn’t been seen since the 1970s. Researchers now say it was caused by a combination of storms, ocean currents, and atmospheric heat.

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• Huge hole seen in Antarctica’s sea ice in 2017, as big as Switzerland
• Occurred over Maud Rise, far from Antarctic coast
• First spotted in 1970s, vanished, then reappeared decades later
• Scientists call it a polynya—open water surrounded by sea ice
• Weddell Gyre sped up, pulled warm salty water upward
• Warmer water melted ice from below, creating open gap
• Extratropical storms pushed sea ice outward, worsening melting
• Atmospheric rivers added heat from above, aiding polynya growth
• Ekman transport pushed salty surface water over Maud Rise
• Hole closed by September 2017, but mystery sparked global study