"On-site measurements in the Southern Ocean still require enormous efforts, so they are quite limited".
Ocean convection occurs within the polynya bringing warmer water to the surface that melts the sea ice and prevents new ice from forming.
The polynya measures some 30,000 square miles, National Geographic added.
Antarctica is going through winter season these days.
Scientists weren't expecting the polynya to re-appear, and aren't sure why it has resurfaced twice in the past two years. It's unusual for one very good reason: while most polynyas occur near coastlines, the Weddell is far inland and relatively sheltered from the violent winds and turbulent seas that generally cause them.
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Scientists first saw it in 1974. Until now, the area has remained frozen over.
According to scientists, finding the hole was only with the help of satellite images. While far smaller than it was in the '70s, it was still interesting since it hadn't been around for over four decades.
Though Moore thinks marine animals could be using this hole to breathe, it is still unclear why it reopened after so many years, what long-term effect it could have on Antarctica's oceans and climate, or if it was triggered by climate change or any other process. Meanwhile, the repeated appearances support the hypothesis which says that the Weddell Polynya is not the one-time incident though it may be had appeared several times in the past.
Now, in 2017, it has considerably increased in size. The hole was about 80,000 square kilometres in diameter at its largest, making it the biggest ever polynya in Antarctica's Weddell Sea since the 1970s.
"The polynya is like a big window", Martin told Earther.
Lead Image: Winter sea ice blankets the Weddell Sea around Antarctica with massive extra-tropical cyclones hovering over the Southern Ocean in this satellite image from September 25, 2017. "We don't have enough observations of the Southern Ocean yet". Then it reheats in deeper areas, allowing the cycle to continue. "Maybe [the Weddell polynya] contributes to that".