A23a Antarctic iceberg may vanish within weeks as it melts

A colossal Antarctic iceberg that broke from the continent nearly 40 years ago is rapidly disintegrating in warmer South Atlantic waters and could vanish within weeks, scientists said. The megaberg known as A23a, which calved from the Filchner Ronne Ice Shelf in 1986 and later became one of the largest and oldest icebergs on record, has been shrinking and fragmenting as it drifts northward after escaping the Weddell Sea in 2020.

Satellite analyses show A23a has lost more than half its mass since earlier this year and now measures about 1,770 square kilometres, roughly 683 square miles. Estimates and public comparisons to landmarks have varied, with descriptions ranging from twice the size of Greater London to sizes likened to Cornwall or a Hawaiian island. In recent weeks, enormous sections measuring as much as 400 square kilometres have broken away, and numerous smaller pieces that still pose hazards to shipping litter the surrounding seas, according to Copernicus and other satellite-observation analyses cited by news agencies.

Physical oceanographers monitoring the berg said its decline has accelerated as it entered warmer waters and encountered larger waves. Andrew Meijers of...