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A polynya is an area of open water surrounded by sea ice.〔W.J. Stringer and J.E. Groves. 1991. (''Extent of Polynyas in the Bering and Chukchi Seas'' )〕 It is now used as geographical term for an area of unfrozen sea within the ice pack. It is a loanword from (ロシア語:полынья) (polynya) (:pəlɨˈnʲja), which refers to 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 and A. Petermann. 1866. ''Proceedings of the Royal Geographical Society of London'', Vol 12 no 2 1867–1868 pp 92–113 (On the Exploration of the North Polar Region )〕〔(polynya ), Merriam Webster Dictionary〕 In past decades, for example, some polynyas, such as the Weddell Polynya, have lasted over multiple winters (1974–1976).〔(Weddell Polynya ), NASA, 1999〕 == Formation == Polynyas are formed through two main processes: * Sensible heat polynya: this is thermodynamically driven, and typically occurs when warm water upwelling keeps the surface water temperature at or above the freezing point. This reduces ice production and may stop it altogether. * Latent heat polynya: 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 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 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「polynya」の詳細全文を読む スポンサード リンク
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