Huge holes have popped up randomly on the surface of Weddell Sea in Antarctica since at least the 1970s. For years, scientists have been baffled about their appearance and mysterious origin.
With the help of high-tech seals and floating robots, researchers may finally have an answer. The holes — known as polynyas — may be the result of storms and salty ocean conditions.
One hole that surfaced in 2016 and 2017 captured the attention of scientists. It was the first time oceanographers were able to monitor such a newly formed gap in the sea ice.
"Observations show that the recent polynyas opened from a combination of factors — one being the unusual ocean conditions, and the other being a series of very intense storms that swirled over the Weddell Sea with almost hurricane-force winds," said lead author Ethan Campbell, a University of Washington doctoral student in oceanography, in a statement.
The study, which was published in the journal Nature, used satellite images of the sea ice cover, robotic drifting floats and even seals temporarily outfitted with sensors to collect data. The elephant seal shown above is outfitted with a temporary satellite tag, which allows it to collect data about ocean conditions.
A perfect storm
Polynya is Russian for "open water" or "hole in the ice." A polynya can form near the shore as wind pushes ice around. A polyna can also appear far from the coast and linger for weeks to months, where it acts as an oasis for penguins, whales and seals, giving them a spot to pop up and breathe.
"This study shows that this polynya is actually caused by a number of factors that all have to line up for it to happen," said co-author Stephen Riser, a UW professor of oceanography. "In any given year you could have several of these things happen, but unless you get them all, then you don't get a polynya."
Researchers found that when winds draw nearer to shore, they create conditions that force warm water up from the sea floor. In addition, in the periods those polynyas were observed, the surface ocean was especially salty. When the saltier water gets churned up, is chilled on the surface and becomes denser than the water below it, ice can't form.
"Essentially it's a flipping over of the entire ocean, rather than an injection of surface water on a one-way trip from the surface to the deep," said co-author Earle Wilson, who recently completed his doctorate in oceanography.