How World’s Largest Iceberg Escapes Ocean Whirlpool

Initially stuck in the Weddell Sea for decades, Iceberg A-23A was eventually caught in a Taylor column after regaining mobility. It remained trapped for several months, showcasing the dynamic and unpredictable nature of iceberg movements influenced by oceanic and seabed features, the SciTechDaily reported.

When icebergs break away from ice shelves or large glacier fronts, they become travelers in the ocean, carried by currents, spinning in eddies, shifting with the tides, and pushed along by the wind. Sometimes, these massive ice chunks get stuck — either grounded on a shallow seafloor or caught in a swirling mass of water. Iceberg A-23A experienced both.

After calving from the Filchner-Ronne Ice Shelf in 1986, Iceberg A-23A spent decades immobilized on the seafloor of the southern Weddell Sea. In the early 2020s, it started to break free, and by March 2023, the iceberg, roughly the size of Rhode Island, was floating freely. However, its newfound mobility was short-lived. By March 2024, as it drifted northward, A-23A became trapped again — this time in a Taylor column, a rotating vortex of water created when currents meet an obstacle on the seafloor.

While every iceberg’s journey is unique, most follow the same general path. More than 90 percent of bergs around Antarctica enter the clockwise-flowing current of the Weddell Gyre off East Antarctica and eventually escape, shooting north along the Antarctic Peninsula and finally out across the Drake Passage into warmer South Atlantic waters—an ocean route known as “iceberg alley.”

The motion of A-23A, however, appears quite out of the norm. For about eight months, the berg rotated tightly within the Taylor column about 200 kilometers (120 miles) north of the South Orkney Islands. According to Jan Lieser, an ice specialist with the Antarctic Meteorological Service who has been tracking the berg, A-23A made 15 revolutions between March and November 2024. “I am not aware of an iceberg that has been trapped in such a persistent manner in such a small area,” Lieser said.

The animation at the top of this page shows the iceberg between November 5 and December 16, 2024. Notice that by about mid-November, the berg appears to “spin out,” escaping the vortex and resuming its northeastward journey. Images for the animation were acquired by the MODIS (Moderate Resolution Imaging Spectroradiometer) and VIIRS (Visible Infrared Imaging Radiometer Suite) instruments on several NASA and NOAA satellites.

Christopher Shuman, a University of Maryland, Baltimore County, scientist based at NASA’s Goddard Space Flight Center, estimated that the berg drifted about 240 kilometers in one month since exiting the vortex. In other words, it traveled about 8 kilometers per day as it continued to rotate on its way to the northeast.

It is still unclear what might have nudged the berg from the vortex. “My hypothesis is that a random perturbation in the system might have triggered a slight variation of the ‘usual’ spin, such that the iceberg found an exit path,” Lieser said.

“This serves to remind us both of the mysteries of our oceans and the value of remote sensing data,” Shuman said. Cryospheric scientists will continue using satellites to observe changes to the ice in this remote part of the planet—including but not limited to icebergs.

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