And that means more food for everyone.

Thanks to Linode for supporting this SciShow video! Despite all the water involved, much of the Arctic and Antarctic get so little precipitation that they are literally deserts. These deserts have their own version of an oasis - called polynyas - which are gaps in the sea ice that can be up to thousands of square kilometers in size. Polynyas are a critical part of the polar ecosystem, and they have a larger role to play, like affecting how ocean currents churn around the globe.

There are two kinds of polynyas, and each tends to form in a different way. Coastal polynyas form when winds coming from the land push ice away from the shore, while open ocean polynyas form when warm ocean water rises up from the depths and either melts a hole in the ice from below or prevents ice from forming in the first place.

When polynyas form, they provide an oasis for an entire polar ecosystem. Microscopic plants called phytoplankton, which need sunlight to make their food, can grow in the absence of a thick layer of ice. This surge in life quickly travels up the food chain, attracting zooplankton, fish, whales, seals, and penguins. Polynyas are also essential gateways for creatures that breed on land, but hunt in the water. For example, 96% of the Antarctic elephant seals that one research team tracked used polynyas to hunt. Meanwhile, research has shown that the more phytoplankton growing in a polynya, the larger the size of a nearby Adélie penguin colony. The distance between the colony and the polynya is important, as it determines how long penguins have to fast while looking after their egg or chick. Researchers have observed that if a nearby polynya doesn’t form, male Adélie penguins fast for longer, lose more body weight during nesting, and fewer eggs end up hatching. On the other side of the planet, polynyas play a crucial role in the lives of the humans that call the Arctic desert home. Pikialasorsuaq, also called the North Water Polynya, opens every year in the ice between Northern Canada and Greenland. It’s the largest polynya in the Arctic and relies on both coastal and open ocean effects to keep it free of ice. Inuit communities have relied on this polynya for thousands of years, as its productive ecosystem makes it a perfect hunting ground and its open waters have long provided both a migration and two-way trade route.

However, like many parts of the polar climate, polynyas and the conditions that form them are rapidly changing. According to a study published in 2021, Pikialasorsuaq shrank between roughly 2,500 and 1,000 years ago. This meant less phytoplankton growth and fewer birds for people to hunt. A few hundred years into this period, humans abandoned their settlements in Greenland, though the team couldn’t prove if this was only because the polynya was smaller or due to larger climate effects. They do predict the modern climate crisis could produce a similar decline in this Arctic ecosystem.

More generally, having fewer polynyas form could have global effects. Polynyas create dense water that sinks towards the ocean floor, pushing other water out of the way. This isn’t just localized churning - polynyas, particularly in the Antarctic, help drive currents that encircle the globe and play a critical role in moving colder and warmer water where it wouldn’t normally go. For example, the Gulf Stream is a current that carries heat from the tropics towards Europe, making the continent warmer than it should be, given how far north it is. Without polynyas, entire continents might be a lot less pleasant to call home.

Furthermore, polynyas can also pull carbon dioxide out of the atmosphere and store it on the seafloor. Phytoplankton use carbon dioxide as a part of their food-making process and when they die, their corpses sink to the seafloor and store the carbon. Scientists aren’t exactly sure how the climate crisis will impact how well polynyas work as carbon storage systems or as global water circulators. But polynyas can be pretty tricky to study, since it’s often difficult to get to the poles during the winter when they’re more active. More research is needed to figure out what polynyas can do - not just for the animals and people who live near them, but for every bit of life that calls Earth home.