Mental Floss

1 Trillion-Ton “Megaberg” Is Roaming the Ocean Once Again

Penguins may have a problem on their hands.

ByJake Rossen|
Shot of A23a taken from space.
Shot of A23a taken from space. | MODIS Land Rapid Response Team, NASA GSFC via Wikimedia Commons // Public domain

For over 30 years, an iceberg roughly the size of Rhode Island and estimated to weigh over 1 trillion metric tons has been stuck in place in the Weddell Sea along the Antarctic coastline. Now, the “megaberg” is back in motion.

Dubbed A23a, the ice formation is almost unfathomably huge. It measures 1500 square miles, with an ice thickness of 1312 feet. Originally part of the Filchner-Ronne ice shelf in Antarctica, it calved—or splintered off—in August 1986, taking a Soviet-era research station along for the ride. The freedom was fleeting, however: The berg quickly ground to a halt when it ran up against the Weddell Sea floor.

According to the British Antarctic Survey, the ice giant didn’t begin moving again until 2020, when ocean currents and winds began nudging it along. It came to a stop a second time in August of this year—at least in terms of forward movement—when it became lodged in a spinning ocean vortex known as a Taylor column that rotated it by 15 degrees every day. Only recently has the behemoth moved free of the dizzying purgatory.

An A23a iceberg illustration is pictured
A23a has been busy. | Anadolu/GettyImages

The sight was a once-in-a-lifetime experience for crew members of the RRS Sir David Attenborough, a research vessel that came close to the iceberg in 2023 during an expedition. Scientists took the opportunity to sample the surrounding water to see how the ice block may be affecting the immediate area. The mineral deposits given off by the ice can be a nutrient source for organisms lower on the food chain.

“In many ways these icebergs are life-giving—they are the origin point for a lot of biological activity,” Dr. Catherine Walker of the Woods Hole Oceanographic Institution told the BBC.

Barring any further interruption, the Antarctic Circumpolar Current is expected to carry A23a toward South Georgia Island, where famed explorer Ernest Shackleton wound up after his ship, Endurance, was crushed by ice. It’s there where the iceberg could transform from a curiosity to an environmental threat; depending on where it settles, it may block penguins and seals from feeding routes. Ultimately, warmer weather will likely be its undoing.

Incredibly, A23a is not the biggest megaberg on record. A formation known as B-15 with a surface area of 4250 square miles floated free in 2000.

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