Title of World's Largest Iceberg Has Transferred

After nearly four decades, one of the world's largest and oldest icebergs is finally breaking up. Known as A23a, this massive chunk of Antarctic ice originally calved from the continent's shelf in 1986 and spent more than 30 years grounded in the Weddell Sea before eventually floating free. At its peak, A23a weighed around 1.1 trillion tons and measured 1,418 square miles, a mass bigger than Rhode Island, per CNN. According to satellite data analyzed by the EU's Copernicus Earth observation program, the iceberg is now less than half its original size, though still massive—about 683 square miles, per the Guardian.

Earlier this year, A23a briefly ran aground near South Georgia island, prompting concerns that it might impede local penguin and seal populations, but it soon moved on. "It has been following the strong current jet known as the Southern Antarctic Circumpolar Current Front (SACCF) anti-clockwise around South Georgia ever since," Andrew Meijers, a physical oceanographer with the British Antarctic Survey, tells CNN. But now, "it's very much on its way out," he says, per the Guardian. "It's basically rotting underneath."

Recent weeks have seen large sections—some as big as 150 square miles—break away, with smaller fragments also posing potential hazards for shipping. With the breakup, A23a moves to second place in the battle of massive icebergs and will likely continue dropping down the list for the next few weeks as it becomes unrecognizable. The title of world's largest iceberg is now claimed by D15a, measuring about 1,158 square miles. At present, that iceberg is "fairly static on the Antarctic coast near the Australian Davis base," Meijers tells CNN.