weddell sea

The last days of a giant iceberg

October 23, 2025 By EarthWise Leave a Comment

A colossal iceberg known as A-23A broke off from the Filchner Iceshelf in Antarctica in 1986. At that time, it was 1,418 square miles in area, slightly larger than the state of Rhode Island, or roughly twice the size of greater London. It weighed about a trillion tons. It was the largest iceberg ever observed.

After breaking off from the iceshelf, it lodged on the seafloor of the southern Weddell Sea for decades. It finally broke free in the early 2020s and began drifting northward. Last year, it got caught up in a rotating ocean vortex in the Drake Passage, and then became lodged on a shallow coastal shelf south of South Georgia Island. More recently, satellite imagery has shown A-23A to be on the move again.

Like other large icebergs that have found their way into the so-called “iceberg alley”, it is gradually succumbing to the effects of warmer air and water. Two large fragments of A-23A have already calved from it. These are huge in their own right: A-23G and A-23I are each over 125 square miles in area. The remaining main body of A-23A is still 580 square miles in area, making it the second largest freely floating iceberg in the world as of September. It had already lost much of its area since it began drifting north.

As it continues to drift northward, A-23A will continue to break apart. Many smaller pieces are littering the sea in its vicinity, but even these are large enough to threaten ships. The 40-year saga of iceberg A-23A is coming to an end.

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A Giant Iceberg’s Final Drift

Photo courtesy of the Earth Observatory at NASA.

Earth Wise is a production of WAMC Northeast Public Radio

The largest iceberg runs aground

April 10, 2025 By EarthWise Leave a Comment

The largest iceberg in the world, which has been slowly drifting for nearly 5 years, has finally come to a halt. The iceberg – called the unexciting name A-23A – came into existence in 1986 when it broke off from another iceberg A-23 that had calved or torn off from Antarctica earlier that year. For decades, A-23A sat in the Weddell Sea, east of the Antarctic Peninsula. Then, in 2020, it came loose from the seafloor and began to move. By 2023, it finally left Antarctic Waters.

Late last year, it began spinning in place caught in an ocean current called a Taylor column. Finally, it headed for South Georgia, a British-owned island that is home to a couple dozen people and lots of seals and penguins. A-23A is now stuck on the continental shelf, about 50 miles from the island.

A-23A is around 1,300 square miles in area. By comparison, New York City is 300 square miles.

Four years ago, a large iceberg called A-68A also came to ground in the vicinity of South Georgia. It quickly broke apart and ultimately added 150 billion metric tons of fresh water to the ocean as well as various nutrients. A-23A is also likely to succumb to the warmer waters, winds, and currents it now encounters and will affect the flora and fauna in the area.

The climate is changing and is impacting how ice shelves melt. Calving and the creation of mammoth icebergs are a normal part of the lifecycle of polar ice sheets, but we are likely to see even more events like this in the future.

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World’s Largest Iceberg Runs Aground

Photo, posted January 29, 2011, courtesy of Drew Avery via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Antarctic Ice Collapse | Earth Wise

March 2, 2022 By EarthWise Leave a Comment

In Antarctica, a huge chunk of the Larsen B Ice Shelf collapsed suddenly and spectacularly in January.

The Larsen Ice Shelf is located on the northeastern side of the Antarctic Peninsula on the Weddell Sea. It was formed over the course of more than 12,000 years. The Weddell Sea used to be a completely frozen body of water. The famous Ernest Shackleton expedition in 1915 was trapped in its ice. But the Antarctic Peninsula has been steadily warming in recent decades.

The Larsen A Ice shelf collapsed in 1995 and the 1,250-square-mile Larsen B Ice Shelf collapsed in 2002. After that event, a portion of the detached ice shelf refroze in 2011 and was attached to the Scar Inlet Ice Shelf. The refrozen ice was called the Larsen B embayment.

In January, the embayment broke apart, taking with it a portion of the Scar Inlet Ice Shelf. It disintegrated within a matter of days. The combined Larsen Ice Shelves – called A, B, C, and D – once extended along a 1000-mile stretch of the eastern Antarctic Peninsula. Since 1995, it has shrunk from 33,000 square miles to 26,000 square miles.

These ice shelves float on the ocean, so their loss does not actually increase global sea levels. However, the shelves act as dams that hold back glaciers located on the land behind them. The loss of Antarctic ice shelves dramatically increases the rate at which glaciers flow into the sea, and that does increase global sea levels.

Now that the sea ice from the Larsen B embayment is gone, it is likely that there will be additional inland ice losses from the newly exposed glaciers.

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Remnant of Antarctica’s Larsen B Ice Shelf Disintegrates

Photo, posted February 13, 2018, courtesy of NASA/Nathan Kurtz via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.