Antarctica’s winter ice opened into a vast stretch of ocean. Scientists traced what went wrong

In the middle of Antarctica’s winter, a vast patch of ocean appeared where sea ice normally covered the water. The opening in Breid Bay reached roughly 34,400 square miles , an area almost the size of Portugal. Now, research published September 27 in Geophysical Research Letters offers an explanation: extraordinary conditions in the atmosphere and ocean worked together to prevent the winter ice from holding.

The event happened in August 2024 , rather than this week. Scientists call such an opening a polynya : an area of open water within surrounding sea ice. It was the first winter open-ocean polynya observed in this East Antarctic sector during the satellite record beginning in 1979. Its appearance raised a question with consequences beyond a striking satellite image: how could so much water remain exposed during the season when ice should be growing?

What opened the ice and why it matters beyond Antarctica

The researchers identified six intense atmospheric rivers during July and August, accompanied by unusually warm air, clouds, snowfall and strong winds. These conditions reduced winter cooling and hindered ice growth. Meanwhile, wind-driven upwelling brought warmer water toward the surface, adding heat from below. The study describes a combination of forces, rather than a single storm suddenly punching through an otherwise stable ice cover.

An atmospheric river is a long, narrow corridor carrying water vapor through the sky. The name can sound exotic, but the phenomenon is familiar to many Americans: these systems can deliver substantial rain and snow, replenish water supplies and, when especially powerful, cause damaging floods. NOAA emphasizes that their effects depend on their strength and the conditions where they arrive. The same broad weather mechanism can have very different consequences in California and Antarctica.

Understanding the Antarctic opening starts with distinguishing sea ice from the ice sheet on land . Sea ice forms when seawater freezes and floats on the ocean. Antarctica’s ice sheet is the enormous mass of ice covering the continent. A polynya is an opening in that floating sea-ice cover; it is not a crater through the continent or evidence that an entire section of the land-based ice sheet disappeared.

That distinction also answers an immediate concern: melting floating sea ice does not substantially raise sea level directly . NASA compares it to an ice cube melting in a glass of water, because the floating ice already displaces water. Ice lost from land is different. When glaciers and ice sheets release water into the ocean, they add to its volume. For coastal communities, that is the connection that matters when assessing long-term flooding risks.

Floating ice still provides important protection. Research summarized by the National Snow and Ice Data Center shows that sea ice can buffer Antarctic ice shelves against ocean swells. Without that protection, waves can flex and weaken vulnerable shelf edges. Ice shelves, in turn, help slow the movement of ice from the continent into the sea. This is a broader physical connection, not evidence that the Breid Bay opening itself caused an ice-shelf collapse or a measurable rise in coastal water levels.

Sea ice also helps regulate how much solar energy the planet absorbs. Its bright surface reflects sunlight, while darker ocean water absorbs more of it. NASA identifies this contrast as a key reason changes in ice cover matter to the climate system . An opening during winter should not be treated as equivalent to summer ice loss, when sunlight is abundant, but the seasonal timing and persistence of exposed water are important parts of the picture.

There is an ecological side, too. Polynyas are natural features and can support rich marine life. Nutrients and open water help sustain phytoplankton, the microscopic organisms at the foundation of ocean food webs. In Antarctica, those food webs support krill, penguins, seals and whales. Their existence is therefore not automatically a sign of damage; what scientists need to understand is how changes in their location, timing and duration affect the surrounding system. National Snow and Ice Data Center.

For readers following alarming ice headlines, the useful questions are straightforward: When did it happen? Was the ice floating or on land? What did researchers actually measure? Antarctic sea ice varies considerably from year to year, and NSIDC stresses the importance of continued observations when assessing longer-term shifts. The Breid Bay research helps explain an exceptional event. Understanding whether similar openings become more common and what follows when they don requires watching beyond a single dramatic image.