A hole the size of Maine has opened up in Antarctica's Weddell Sea and scientists aren't sure why.
Holes are by no means new phenomena in Arctic or Antarctic sea ice. They are known as "polynyas" and traditionally form near coasts in polar regions. This one, however, is deeper and farther from the ice edge than scientists have studied.
"It looks like you just punched a hole in the ice..." said atmospheric physicist Kent Moore, who teaches at the University of Toronto and works with the Southern Ocean Carbon and Climate Observations and Modeling group at Princeton, according to VICE. "...If we didn't have a satellite, we wouldn't know it was there."
A polynya occurred in the same location in 1970s. Moore said scientists did not possess the technology to study it at the time. Four decades passed before the hole opened up for a few weeks in 2016. It then reopened on Sept. 9.
This year's hole reached a maximum size of about 30,000 square miles, making it the largest since the 1970s polynya, National Geographic reports.
Professor. Dr. Mojib Latif, head of the Research Division at GEOMAR Helmholtz Centre for Ocean Research Kiel, explained to Phys.org how the so-called Weddell Polynya forms:
"The Southern Ocean is strongly stratified," Latif said. "A very cold but relatively fresh water layer covers a much warmer and saltier water mass, thus acting as an insulating layer."
The warm bottom layer can melt the ice if it reaches the surface.
"This is like opening a pressure relief valve," Latif said. "The ocean then releases a surplus of heat to the atmosphere for several consecutive winters until the heat reservoir is exhausted."
Moore told VICE that the temperature contrast between the ocean surrounding air can drive convection, which causes cold water to sink to the bottom of the ocean and warmer water to come to the surface.
"[This] can keep the polynya open once it starts," Moore said.
What scientists don't yet understand is how often the polynya occurs and why it has occurred twice in the past two years after being dormant for more than four decades. Scientists cannot confirm whether it is linked to climate change.
Scientists at the GEOMAR center developed a model, the Kiel Climate Model, that predicted the Weddell Polynya would occur again despite American models indicating otherwise, Phys.org reports. Although there is still much left to study, the appearance of the hole confirms the Kiel Climate Model's applicability to future research investigating the natural and human processes driving this phenomenon.
"Global warming is not a linear process and happens on top of internal variability inherent to the climate system," said Latif. "The better we understand these natural processes, the better we can identify the anthropogenic impact on the climate system."