What about that hole in the sea ice?

There’s been discussion about a big opening in sea ice, called a polynya, and if it had anything to do with the Russian expedition ship, Akademik Shokalskiy, getting stuck near the Antarctic coast. The answer is not so straightforward. “In the winter, polynyas can close up really quickly,” said Kevin Arrigo, a professor at Stanford University. When they close, whatever is inside may be trapped. Polynyas allow access to Antarctica’s shores, and most Antarctic research stations exist where they do because of polynyas. Winds blow, push the ice off the shore, and create holes in the sea ice. Ships want to go into these open spaces. “If the winds stop blowing, polynyas can just freeze over and fill in,” Arrigo said. That is partially what happened with Akademik Shokalskiy, but not the full picture. Also, polynyas are not only an essential component of navigating sea ice; they are vital to polar ecosystems. Here’s why:

On the horizon

Most of the polynyas around Antarctica are wind driven. “In many ways, where those winds blow depends on topography, by the shape of the hills and mountains,” Arrigo said. Strong winds, known as katabatic winds, come off the cold ice sheet, flow downhill and continually blow ice off of the coastal shore.

McMurdo Station McMurdo Station sits on Ross Island in McMurdo Bay in Antarctica. It is a critical access point for ships to resupply researchers. The station also houses the largest population of about 1200 people on the continent. The Ross Sea polynya is visible in the distance. Credit: Ted Scambos, NSIDC

Many polynyas recur in the same region year after year—a useful manual for navigating the waters. “Having open water reoccur in the same region at certain times of year, makes it possible to get ships in and out,” said Seelye Martin, a professor at the University of Washington. McMurdo Station, a research base on Ross Island in Antarctica, exists because of the Ross Sea polynya, which forms in October and November. It’s also a reason why the base is important to the history of exploration. In the early 1900s, Robert F. Scott and Ernest Shackleton ventured into the continent from this entry point in part because of the polynya, which enabled ships to approach the land. Polynyas vary dramatically in shape and size, some deceivingly large. When early explorers ventured into open waters, they often mistook the expanse for new sea. Still, others have seen something even more peculiar. “When I used to work in the Arctic,” Martin said, “we would see these cloudy regions, thinking that we were seeing signs of industrial activity.” But really it was a polynya at work, generating low clouds and fog. “We called it sea smoke,” he said. This sea smoke billows, forming a warm microclimate like, for instance, the North Water Polynya, on the northern end of Baffin Bay off the Greenland coast. This polynya provides refuge for big mammals: narwhal, walrus, and various species of whales to feed and rest. So more happens within these open waters than meets the eye.

The light switch

NASA image of a Ross Sea polynya The image from 2004 above shows a polynya (the dark opening) in the Ross Sea near Antarctica. The polynya is located just north of the Drygalski Ice Tongue. Giant icebergs float from shore to the right of the image. And in the dark open water, herded ice crystals generate streaks, which move parallel to the wind. Credit: NASA Moderate Resolution Imaging Spectroradiometer (MODIS)

The polar regions see no light in their respective winters. “That’s when polynyas become little ice engines,” Martin said. When winds push the ice pack away, near freezing point water temperatures generate more ice. The wind pushes formed ice crystals with the wave, piling them against the edge of a polynya, like swelling debris on a shore. Long streaks of ice crystals form. “You can look at a satellite image and spot the polynyas because they look like corduroy,” Martin said. Along with wind, another environmental force forms polynyas: ocean upwelling. Upwelling, or the movement of deep, dense, and nutrient-rich waters toward the ocean surface, causes most open-ocean polynyas—though this process is much less common. “Over a big chunk of the world there is a layer of warm water that sits between 200 meters and 800 meters,” Arrigo said. “Anytime that water makes it up to the surface, it has the ability to melt ice.” Sometimes wind sweeping and upwelling maintain the same polynya. Then spring comes and something else happens.

Common Eider rests in Arctic For the Common Eider, a duck species that lingers year-round in the Arctic, polynyas are a matter of survival. It breeds in the Arctic, diving for mollusks and mussels. The male is unmistakable with its black and white plumage and green nape. The female is brown. The image above captures the Common Eider resting on rocks near Kirkcaldy Fife, Scotland. Credit: Gordon Ednie, flickr.com

“Come early spring, polynyas are ice free first,” Arrigo said, “but phytoplankton in these high latitude waters can’t start growing until the light is turned on.” And when light appears, so do the first signs of life. The lack of sea ice in polynyas permits sunlight to reach the upper ocean layers. Sunlight, combined with the warmer temperatures, causes polynyas to brim with phytoplankton. This primary food source turns polynyas into feeding lots for fish, seals, penguins, and other marine mammals. “Polynyas are cool things,” Arrigo said. “They’re basically these oases in areas of the ocean where you would not expect to find much life.”

An undulating system

Sea ice, however, is dynamic. For the Akademik Shokalskiy, it wasn’t merely a shift in the wind pattern, but in part, a past event—the breaking of a glacier—catching up to it. Blocks of the glacier floated in, surrounding the ship. Something similar happened in the Ross Sea in 2000 and 2002 when ice broke off the ice shelf: the Ross Sea Polynya almost didn’t form. “The winds were blowing right but the ice had nowhere to go,” Arrigo said. Gigantic icebergs blocked the flow of ice—and shut down food production. “That was a really bad year for the animals,” he added. “Overall, however, we wouldn’t have nearly as many penguins in Antarctica where it not for polynyas.” And we wouldn’t have nearly as many ships transporting researchers to study them.