Polynya

A polynya (common US spelling) or polynia (common UK spelling) (pron-en|pəˈlɪnjə) is an area of open water surrounded by sea ice. It is now used as geographical term for areas of sea in Arctic or Antarctic regions which remain unfrozen for much of the year. It is a loanword from _ru. полынья, IPA-ru|pəlɨˈnʲja, which means a natural ice hole, and was adopted in the 19th century by polar explorers to describe navigable portions of the sea. [Sherard Osborn, Peter Wells, A Petermann "Proceedings of the Royal Geographical Society of London" Vol 12 no 2 1867-1868 pages 92-113 On the Exploration of the North Polar Region]

Formation

Polynyas are formed through two main processes:

* The first mechanism for polynya formation is thermodynamically driven, and occurs when the surface water temperature never reaches the freezing point. This may be due to a region of warm water upwelling, which reduces ice production and may stop it altogether. This type of polynya is called a Sensible Heat Polynya.

* The second type of polynya is called a Latent Heat Polynya and is formed through the action of katabatic wind or ocean currents which act to drive ice away from a fixed boundary, such as a coastline, fast ice, or an ice bridge. The polynya forms by initially 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 first year pack ice. The latent heat polynya is the open water region between the coast and the first year ice pack.

Latent heat polynyas are regions of high ice production and therefore are possible sites of dense water production in both polar regions. 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 masses. It is an open question as to whether the polynyas of the Arctic can produce enough dense water to form a major portion of the dense water required to drive the thermohaline circulation.

Ecology

Some polynyas, such as the North Water Polynya in Canada, 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. 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) fixed by planktonic microalgae to Arctic cod, seals, whales, and polar bears.

References

* [http://www.fsg.ulaval.ca/giroq/now/ International North Water Polynya Study (NOW)]

External links

* [http://www.atmosp.physics.utoronto.ca/ANTARCTIC/weddell_polynya.html Weddell Polynya]
* [http://www.bartleby.com/61/74/P0427400.html The American Heritage Dictionary of the English Language: Fourth Edition on "polynya"]
* [http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17407 Polynya north of Alaska] at NASA Earth Observatory
* [http://pubs.aina.ucalgary.ca/arctic/Arctic44-S-164.pdf Polynyas in the Bering and Chukchi Seas]