During winter, the Bering Strait has historically been blanketed in ice. But this year, the ice has nearly vanished.

"The usually ice-covered Bering Strait is almost completely open water," Zack Labe, a climate scientist and Ph.D. candidate at the University of California at Irvine, said over email.

At its narrowest point, the Arctic strait between the U.S. and Russia is 55 miles across, and there's a prominent theory that people once crossed from Asia into North America across an exposed Bering land bridge (back when sea levels were lower). In modern times, however, this frigid waterway usually builds ice through the winter, reaching its greatest extent in late March.

After that, the ice usually lingers for months.

"There should be ice here until May," Lars Kaleschke, a climate scientist at the Alfred Wegener Institute for Polar and Marine Research, said over email.

A new record low sea ice extent for the day of the year in the Bering Sea. pic.twitter.com/DuznyRcKV4 — Lars Kaleschke (@seaice_de) March 3, 2019

But now, in early March, the ice extent is the lowest in the 40-year satellite record, said Labe. On March 2 specifically, the ice extent was lowest on record for that day of the year, added Kaleschke.

Overall, the last two years have now seen exceptionally low ice cover in the Bering Sea, and there are a few reasons why.

In the longer-term, the Arctic is warming over twice as fast as the rest of the globe, leading to significant melting across much of the Arctic, even where the ice is the thickest, oldest, and most resilient. "The 12 lowest extents in the satellite record have occurred in the last 12 years," the National Oceanic and Atmospheric Administration's 2018 Arctic report concluded.

This Arctic warming is especially notable near the Bering Strait. "In the long-term, temperatures in northern Alaska have been rising faster than anywhere else in the United States," said Labe.

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"The last two winters in the Bering Sea have been unprecedented in at least the last 40 years."

The ocean might be playing an outsized role in melting the ice too, as sea temperatures have been above average, both Labe and Kaleschke noted. Last year, ice levels remained low even when colder winds blew through the Bering Sea, "pointing to a potential role of anomalous ocean heat," said Kaleschke.

In combination with these longer term warming trends, winds over the last several weeks have "battered the remaining sea ice," said Labe, noting that these same winds have boosted temperatures up to a whopping 30 degrees Fahrenheit above normal.

Another 2019 Alaska #seaice factiod: sea ice extent in the Bering & Chukchi Seas has decreased by 360,000 km² since Jan 25th. That's right, an area the size of Montana has gone from (some) ice to (mostly all) water in six weeks. #Arctic #akwx @Climatologist49 @seaice_de @ZLabe pic.twitter.com/8PcPOQxKkH — Rick Thoman (@AlaskaWx) March 4, 2019

The sum of these conditions has meant profoundly little sea ice in the Bering Strait this year. Though, some ice may likely regrow when the winds shift later this month, said Kaleschke.

But that won't change the greater story of the Bering Strait in 2019. The ice is nearly gone when it should be growing.

"The last two winters in the Bering Sea have been unprecedented in at least the last 40 years," said Labe.