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A Mysteriously Massive Hole in Antarctic Ice Has Returned

These holes are thought to be crucial elements of the currents driving the world’s oceans, and after 40 years, one has formed again

Little is known about the relation between these openings and climate change, but by studying them scientists hope to better tease out our impacts on this delicate system. (Jan Lieser, ACE CRC, Australia)
smithsonian.com

A hole the size of Maine has opened in the wintertime sea ice surrounding Antarctica. Though these holes, called polynyas, are not uncommon around Earth's southernmost continent, one hasn't been spotted in this location since the 1970's, reports Heather Brady of National Geographic. 

The polynya in question opened on September 9 in a relatively shallow area of water in the Weddell Sea. ​At its peak, it spanned roughly 30,000 square miles—about the size of Maine, writes Brady.​ The first hole in this location was spotted in 1974 and was roughly the size of Oregon. It stuck around for another two years, but then disappeared. Since that time, the region has remained largely quiet.

Then in 2016, a gap in the ice appeared, catching scientists attention. The latest hole is the largest the spot has been since the 70's, writes Brady.

These holes in the ice form thanks to Antarctic water circulation, reports Maddie Stone at Earther. Warm water rises toward the surface, melting the ice that sits atop the open ocean waters, creating the polynya "window." Heat is released from the water through this opening, causing the now cooler water to sink. This circulation pushes more warm water toward the surface, which keeps the polynya open. As Stone reports, the hole is expected to close when warm spring air or the addition of freshwater from melting sea ice, slows the circulation of the waters.

The sinking, cold water helps drive parts of the oceanic conveyor belt that moves ocean water around the globe—a major force in regulation of Earth's climate, reports Stone.​ As climate warms there is concern that this conveyor belt could slow down or even halt as the input of cold fresh water increases from melting ice. Less dense than the underlying saltwater, the fresh water stubbornly stays on top of the ocean waters, slowing the churn of the system. 

But the relationship of these polynyas to climate change remains hazy, and studying this latest opening could help provide scientists with some clues. “While many climate models tend to produce such a large open ocean polynya, the feature was viewed more as a disruptive model glitch than a true phenomenon in the past,” Torge Martin, a meteorologist at the Helmholtz Centre for Ocean Research in Kiel, Germany, tells Stone. “Its recurrence supports our hypothesis... that the Weddell Polynya was not a one-time event but possibly occurred regularly in the past.”

How will future climate change affect these features remains unknown. But as Martin explains the reappearance of the large hole may counterintuitively be a positive sign, suggesting that warming is not yet strong enough to suppress the process driving their formation.

But scientists say they can't be certain until more research can be done in this brutally cold and distant region of our planet.​ And researchers are already on the case, using both satellites and robots to explore the region, reports Kate Lunau of Motherboard.

"The better we understand these natural processes, the better we can identify the anthropogenic impact on the climate system," meteorologist Mojib Latif says in a statement.

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