Polynya
Encyclopedia
Sea ice
Sea ice is largely formed from seawater that freezes. Because the oceans consist of saltwater, this occurs below the freezing point of pure water, at about -1.8 °C ....
. It is now used as geographical term for an area of unfrozen sea within the ice pack. It is a loanword
Loanword
A loanword is a word borrowed from a donor language and incorporated into a recipient language. By contrast, a calque or loan translation is a related concept where the meaning or idiom is borrowed rather than the lexical item itself. The word loanword is itself a calque of the German Lehnwort,...
from , pəlɨˈnʲja (polynya or polynia), which means a natural ice hole, and was adopted in the 19th century by polar explorers to describe navigable portions of the sea. In past decades, for example, some polynyas, such as the Weddell Polynya, have lasted over multiple winters (1974–1976).
Formation
Polynyas are formed through two main processes:- Sensible Heat Polynya: this is thermodynamically driven, and typically occurs when warm water upwellingUpwellingUpwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...
keeps the surface water temperature at or above the freezing pointFreezing PointFreezing Point is a news journal in the People's Republic of China which has been the subject of controversy over its criticism of Communist Party officials and the sympathetic ear it lent to a Chinese historian who had criticized official history textbooks...
. This reduces ice production and may stop it altogether.
- Latent Heat Polynya: is formed through the action of katabatic windKatabatic windA katabatic wind, from the Greek word katabatikos meaning "going downhill", is the technical name for a drainage wind, a wind that carries high density air from a higher elevation down a slope under the force of gravity. Such winds are sometimes also called fall winds...
or ocean currentOcean currentAn ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
s which act to drive ice away from a fixed boundary, such as a coastline, fast iceFast iceFast ice is sea ice that has frozen along coasts along the shoals, or to the sea floor over shallow parts of the continental shelf, and extends out from land into sea. In Antarctica, fast ice may also extend between grounded icebergs...
, or an ice bridgeIce bridgeAn ice bridge is a frozen natural structure formed over seas, bays, rivers or lake surfaces. They facilitate migration of animals or people over a water body that was previously uncrossable by terrestrial animals, including humans. The most significant ice bridges are formed by glaciation, spanning...
. The polynya forms initially by the first year pack ice being driven away from the coast, which leaves an area of open water within which new ice is formed. This new ice is then also herded downwind toward the first year pack ice. When it reaches the pack ice the new ice is consolidated onto the pack ice. The latent heat polynya is the open water region between the coast and the ice pack.
Latent heat polynyas are regions of high ice production and therefore are possible sites of dense water production in both polar region
Polar region
Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...
s. The high ice production rates within these polynyas leads to a large amount of brine rejection into the surface waters. This salty water then sinks and mixes to possibly form new water mass
Water mass
An oceanographic water mass is an identifiable body of water with a common formation history which has physical properties distinct from surrounding water...
es. It is an open question as to whether the polynyas of the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
can produce enough dense water to form a major portion of the dense water required to drive the thermohaline circulation
Thermohaline circulation
The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....
.
Ecology
Some polynyas, such as the North Water Polynya in CanadaCanada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, 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 mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s such as walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...
es, narwhal
Narwhal
The narwhal, Monodon monoceros, is a medium-sized toothed whale that lives year-round in the Arctic. One of two living species of whale in the Monodontidae family, along with the beluga whale, the narwhal males are distinguished by a characteristic long, straight, helical tusk extending from their...
s and belugas that do not migrate south, remain there. In spring, the thin or absent ice cover allows light in, through the surface layer as soon as the winter night ends, which triggers the early blooming of microalgae that are at the basis of the marine food chain. So, polynyas are suspected to be places where intense and early production of the planktonic herbivores ensure the transfer of solar energy (food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
) fixed by planktonic microalgae to Arctic cod
Arctic cod
The Arctic cod is an Arctic deepwater fish related to the true cod .-Names:The fish has several common names, including polar cod and Greenland cod...
, seals
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...
, whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s, and polar bear
Polar Bear
The polar bear is a bear native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size...
s. Polar bears are known to be able to swim as far as 65 kilometres across open waters of a polynya.
Arctic navigation
When submarines of the U.S. Navy made expeditions to the North PoleNorth Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...
in the 1950s and 60s, there was a significant concern about surfacing through the thick pack ice of the Arctic Ocean. In 1962, both the USS Skate
USS Skate (SSN-578)
USS Skate , the third submarine of the United States Navy named for the skate, a type of ray, was the lead ship of the Skate class of nuclear submarines...
and USS Seadragon
USS Seadragon (SSN-584)
USS Seadragon , a , was the second ship of the United States Navy to be named for the seadragon, a small fish commonly called the dragonet....
surfaced within the same, large polynya near the North Pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...
, for the first polar rendezvous of the U.S. Atlantic Fleet
U.S. Atlantic Fleet
The United States Fleet Forces Command is an Atlantic Ocean theater-level component command of the United States Navy that provides naval resources that are under the operational control of the United States Northern Command...
and the U.S. Pacific Fleet.
External links
- International North Water Polynya Study (NOW)
- The American Heritage Dictionary of the English Language: Fourth Edition on "polynya"
- Polynya north of Alaska at NASA Earth ObservatoryNASA Earth ObservatoryNASA Earth Observatory is an online publishing outlet for NASA which was created in 1999. It is the principal source of satellite imagery and other scientific information pertaining to the climate and the environment which are being provided by NASA for consumption by the general public...