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Sea ice around Antarctica has reached a record low in four decades of observations, a new analysis of satellite images shows.

As of Tuesday, ice covered 750,000 square miles off the Antarctic coast, below the previous record low of 815,000 square miles in early March 2017. according to analysis By the National Snow and Ice Data Center in Boulder, Colo.

“It’s a truly unique situation,” said Marilyn N. Raphael, a geography professor at the University of California, Los Angeles, who studies Antarctic sea ice. Warmer ocean temperatures may have played a role, but “there are other factors we’ll try to find in the coming months,” she said.

Antarctic sea ice coverage is highly variable from year to year, but overall, it has increased only slightly on average since the late 1970s, when satellite observations began. By contrast, the amount of sea ice in the Arctic, which is warming about three times faster than other regions, has decreased by more than 10 percent over the same period.

The two regions are very different from each other. The Arctic Ocean occupies high latitudes, including the North Pole, and is surrounded by land masses. In the Southern Hemisphere, Antarctica occupies the pole. The Southern Ocean surrounding the continent begins at much lower latitudes and is open to the north.

While rapid warming in the Arctic is largely responsible for the shrinking of sea ice there, the impact of climate change on Antarctic sea ice is much less obvious.

Edward Blanchard-Wrigglesworth, a climate scientist at the University of Washington, said many scientists expect global warming will eventually lead to a decline in Antarctic sea ice. But right now, he said, “it’s really hard to connect the two, especially in terms of singular events like this.”

Instead, a complex set of factors come into play when it comes to Antarctic sea ice. Large-scale atmospheric patterns, which often occur far from the continent, as well as local ocean currents and winds can all increase or decrease sea ice coverage.

For example, Dr. Blanchard-Wrigglesworth said some research has suggested that a strong El Nino in 2015 and 2016, when sea surface temperatures in the tropical Pacific were higher than normal, led to a sharp reduction in sea ice coverage in 2016.

Ted Scambos, senior researcher at the University of Colorado Earth Science and Observation Center, said in an email message that warmer-than-normal sea surface temperatures in some areas around Antarctica may have played a role in the current minimum.

Dr. Raphael said winds can also have an effect, especially in the Amundsen Sea region on the western side of the continent. A region of regularly developing low-pressure air over the sea has been particularly strong this year, leading to stronger winds that may have pushed more ice north into warmer waters, where it would melt faster, he said.

While the overall amount of sea ice has increased only slightly since the late 1970s, the rate of increase began to accelerate in 2000, and the amount of ice reached a record high in 2014. But then something unexpected happened, said Dr. Raphael. It fell drastically over the next three years and hit a record low in 2017.

Dr. Since then, sea ice coverage has recovered and is back to roughly average levels by 2020, Raphael said.

Normally, he said, levels would then continue to be average or above average for several years. But this year’s new sharp decline came earlier. “It happened too quickly,” he said.

“That’s what makes it unusual,” he added. After 2017, “ice returned to normal, but did not stay that way.”

Dr. To understand why the amount of ice is so low, researchers need to examine how conditions have changed over the past year, Blanchard-Wrigglesworth said. “I wouldn’t be surprised to learn that this is the result of wind changes over the last three to six months,” he said.

Low sea ice extent is noticeable in the east of the Antarctic Peninsula in the Weddell Sea, which, due to its circular current, retains much more ice from year to year than elsewhere on the Antarctic coast. A group of scientists and explorers encountered relatively light ice conditions while sailing this month. To search for the wreckage of EnduranceErnest Shackleton’s ship that sank during an Antarctic expedition in 1915.

This year’s amount of ice may drop further depending on the weather, but will soon begin to increase as temperatures begin to drop towards the Antarctic fall and winter seasons. Ice coverage reaches its maximum at the end of September each year. The average maximum in forty years is more than 7 million square miles.

Dr. Events like this and the previous record low offer researchers an opportunity to better understand the link between climate change and sea ice in Antarctica, Blanchard-Wrigglesworth said. “A valid new research question might be, are these the first few indications that a reversal in long-term trends is starting?” said.