A hole the size of Maine—or larger than the Netherlands, depending on which geographic mass means more to you—has opened up in the Weddell Sea in Antarctica. In an otherwise thick layer of sea ice, still frozen from the Antarctic winter, the hole is an aberration.

Ice scientists aren’t sure what’s going on, but they’re all talking about it.

“It looks like you just punched a hole in the ice,” atmospheric physicist Kent Moore, of the University of Toronto, told Vice’s Motherboard.

Moore, along with the Southern Ocean Carbon and Climate Observations and Modelling (SOCCOM) group at Princeton, are studying the mysterious hole, which showed up in satellite images around Sept. 9.

Scientists call holes surrounded by sea ice “polynyas.” National Geographic explains that polynas are created when ocean currents push warm water toward the surface, melting the ice that lies on top. As the surface water comes into contact with the Antarctic atmosphere, it cools and sinks, then heats up again and rises back toward the surface.

This particular polynya previously appeared for multiple seasons in the 1970s. The hole opened up again last year for the first time in four decades, and reappeared, even larger, last month.

Right now, why the hole opened again is a mystery. Moore says it would be “premature” to connect it to climate change, though his team is analyzing data to better understand what could have caused this.

“This is now the second year in a row it’s opened after 40 years of not being there,” Moore told Motherboard. “We’re still trying to figure out what’s going on.”

But Earther notes that another team, from the Helmholtz Centre for Ocean Research in Kiel, Germany, believes its reappearance confirms their climate variability models, which suggested the polynya could show up again.

“While many climate models tend to produce such a large open ocean polynya, the feature was viewed more as a disruptive model glitch than a true phenomenon in the past,” Torge Martin, a meteorologist and climate modeler at the Helmholtz Centre, told Earther. “Its recurrence supports our hypothesis… that the Weddell Polynya was not a one-time event but possibly occurred regularly in the past.”

The news of the hole comes close behind other indications of major change in Antarctica. A few weeks ago, an iceberg over twice the size of Paris broke off from Pine Island Glacier in West Antarctica, in the same place that two other major ice calving events have taken place in recent years. And this week, a new paper published in Geophysical Research Letters found that warming oceans are dramatically undermining the integrity of an important floating ice shelf in West Antarctica. The warm water is carving what Washington Post reporter Chris Mooney called a “huge, upside-down canyon” in the ice sheet from below. The canyon cuts almost halfway through the Dotson ice shelf.

The status of the ice shelf doesn’t have a direct impact on sea-level rise, since it is floating and therefore already displacing as much water as it would if it turned to liquid. But its stability is critically important; like other floating ice shelves, Dotson holds back large glaciers from sliding into the sea, which would definitely affect sea levels.