Полыньи: Области открытой воды в арктических льдах.

Area of unfrozen sea within an ice pack

A polynya (/p//ə/'/l//ɪ//n//j//ə/) is an area of open water surrounded by sea ice. It is now used as a geographical term for an area of unfrozen seawater within otherwise contiguous pack ice or fast ice. It is a loanword from the Russian полынья , which refers to a natural ice hole and was adopted in the 19th century by polar explorers to describe navigable portions of the sea. There are two main types of polynyas: coastal polynyas, which can be found year round near the Antarctic and Arctic coasts and are mainly created by strong winds pushing the ice away from the coast, and mid sea or open ocean polynyas, which may be found more sporadically in the middle of ice pack in certain locations, especially around Antarctica. These locations are generally preconditioned by certain oceanic dynamics. One of the most famous mid sea polynyas is the Weddell Polynya, also known as the Maud Rise Polynya, which occurs in the Lazarev Sea over the Maud Rise seamount. It was first spotted in September 1973 and persisted through multiple winters (1974–1976), and recently recurred in September 2017.

Antarctic Bottom Water is the dense water with high salinity that exists in the abyssal layer of the Southern Ocean. It plays a major role in the global overturning circulation. Coastal polynyas (latent heat polynyas) are a source of AABW as brine rejection during the formation of sea ice at these polynyas increases the salinity of the seawater, which then sinks down to the ocean bottom as AABW. Antarctic polynyas form when ice masses diverge from the coast and move away in the direction of the wind, creating an exposed area of sea water which subsequently freezes over, with brine rejection, to form another mass of ice.

Some polynyas, such as the North Water Polynya between Canada and Greenland, occur seasonally at the same time and place each year. Because animals can adapt their life strategies to this regularity, these types of polynyas are of special ecological research significance. In winter, marine mammals such as walruses, narwhals, and belugas that do not migrate south remain there. Polar bears are known to be able to swim as far as across open waters of a polynya.

The presence of open water in an otherwise ice covered area can result in a localized marine algal bloom, also referred to as a polynya bloom. While algal communities are often found under sea ice, as evidenced by ice algae, the rate of phytoplankton growth is substantially higher in the open water of a polynya. The primary drivers of polynya blooms are sunlight and nutrients. Specifically, the lack of sea ice allows light, a necessary component for photosynthesis, to penetrate deeper into the water and enable elevated phytoplankton growth compared to the surrounding ice covered waters. This influx of nutrients coupled with increased light levels often results in polynya blooms. Therefore, due to the role of primary producers as the foundation of the marine food web, polynyas are a critical food source for a variety of organisms such as fish, birds, and marine mammals. The downward transport of carbon (in the form of marine snow) from the surface to the seafloor associated with polynya blooms provides the nutrients necessary to sustain rich benthic communities.

Polynyas have also supported human populations throughout history. For example, the North Water Polynya, the largest and most biologically productive Arctic polynya, serves as a critical source of food in an otherwise barren region, enabling the existence of high latitude human communities in the region for thousands of years. It may have served as a stepping stone for the original settlers of Greenland as they traversed through what is now northern Canada 4500 years ago.

When submarines of the U. S. Navy made expeditions to the North Pole in the 1950s and 1960s, there was significant concern about surfacing through the thick pack ice of the Arctic Ocean. In 1962, both the USS Skate and USS Seadragon surfaced within the same large polynya near the North Pole for the first polar rendezvous of the U. S. Atlantic Fleet and the U. S. Pacific Fleet.