Known as the Weddell Sea or Maud Rise Polynya, the ice-free zone appeared in September and has grown to as large as 80,000 square kilometres, according to the University of Toronto.
Polynyas, defined as a stretch of open water surrounded by ice, are frequently found in the Arctic and Antarctica, usually near the coast. They rarely reach the extent now seen in middle of the pack ice.
A much smaller polynya opened up in the same Maud Rise region last year for a couple of weeks. Before that, the previous such event there was in the mid-1970s, with the polynya lasting three years and swelling to as much as five times the current size, Moore said.