A huge, mysterious hole has been spotted in sea ice near Antarctica, researchers reported this week.

The hole, which was detected about a month ago, is roughly 30,000 square miles or the size of the state of Maine. It's the largest hole spotted in the Weddell Sea since the 1970s, scientists say.

"In the depths of winter, for more than a month, we've had this area of open water," Kent Moore, professor of physics at the University of Toronto – Mississauga, told National Geographic.

(The months of June, July and August are winter in the Southern Hemisphere.)

This is the second year in a row that scientists have seen such a massive hole in Antarctica's sea ice, though this one is bigger than the one from last year.

The phenomenon is called a "polynya," which is an area of persistent open water where one would expect to find solid sea ice, according to the National Snow and Ice Data Center.

The hole was detected using a robotic float that's capable of operating underneath sea ice. In September, one of these floats surfaced inside the polynya, providing unique data on its existence.

Satellite images further confirmed its appearance.

Moore worked with members of the Southern Ocean Carbon and Climate Observations and Modeling project to investigate polynyas and their climate impacts.

"It's just remarkable that this polynya went away for 40 years and then came back," Moore said.

Without the insulating effect of sea ice cover, a polynya allows the atmosphere and ocean to exchange heat, momentum and moisture, leading to significant impacts on the climate.

The research has not yet appeared in a peer-reviewed scientific journal, as the satellite images were just taken in September, according to University of Tornonto – Mississauga spokeswoman Nicolle Wahl. However, the researchers are submitting this work to the British journal Nature, she said.

Scientists aren’t sure what this polynya will mean for Antarctica’s oceans and climate, and whether it is related to climate change, according to National Geographic.

“We don’t really understand the long-term impacts this polynya will have,” Moore told the magazine.

More:Massive iceberg nearly the size of Delaware breaks off Antarctica

But from these new ocean measurements, along with space-based observations and climate models, the secrets of the polynyas and their impacts on the climate may finally be revealed.

It's been quite a year for ice-related news at the bottom of the world: One of the largest icebergs — estimated at 1 trillion tons — ever recorded broke off from an ice shelf in Antarctica in July. And this week, a paper in the journal Geophysical Research Letters found that warming oceans are dramatically undermining the integrity of an important floating ice shelf in West Antarctica, Quartz magazine reported.