| Term: | Polynya |
| Definition: |
Irregularly shaped areas of persistent open water that are sustained by winds or ocean heat; they often occur near coasts, fast ice, or ice shelves. NSIDCCryosphere
Any non-linear shaped opening enclosed in ice. Polynyas may contain brash ice and/or be covered with new ice, nilas or young ice; submariners refer to these as skylights. Sometimes the polynya is limited on one side by the coast and is called a shore polynya or by fast ice and is called a flaw polynya. If it recurs in the same position every year, it is called a recurring polynya. Polynyas range in size from relatively small to enormous. The largest polynya observed in the Antarctic was the Weddell Polynya of 1975-77, covering an area of 2x105km2. The two main categories of polynya are sensible heat and latent heat, depending on the mechanism responsible for maintaining their presence. Latent heat polynyas are maintained by persistent katabatic winds that drain off the continent. Newly formed ice is advected away by the wind, leaving the surface ice-free and open to more ice formation. In this manner latent heat polynyas can be major sources of new ice production. Coastal polynyas are primarily of this type. Sensible heat polynyas are maintained by upwelling warm water that supplies a sufficiently large oceanic heat flux to the base of the ice to reduce its thickness, or melt it completely. These polynyas are not responsible for large quantities of new ice production. A polynya may also form by a combination of the sensible and latent heat processes. ASPECT2012 A stable ice-free water space in or at the boundary of fast ice. Polynyas may contain very open broken and brash ice or be covered with new ice, nilas or young ice. A polynya is sometimes restricted by the shore from one side and is termed a shore polynya. If it is restricted by fast ice, then it is termed a flaw polynya. If it recurs in the same position every year, it is termed a recurring polynya. Polynyas can form in the pack, e.g. in the Weddell Sea. Bushuyev Any nonlinear-shaped opening in the water but enclosed by ice. Sometimes the polynya is limited on one side by the coast and is called a shore polynya, or by fast ice and is called a flaw polynya. Some polynyi recur annually in the same position. WMOSeaIce Sea ice terminology. Describes any non-linear-shaped opening that is enclosed by ice. May contain brash ice and/or be covered with new ice, nilas or young ice. Submariners refer to polynya's as 'skylights.' ECCCanada Any water area in pack ice or fast ice other than a lead, not large enough to be called open water. If a polynya is found in the same region every year, e.g. off the mouths of big rivers, it is called a recurring polynya. A temporary small clearing in pack ice which consists of small floes and brash in continuous local movement is called an unstable polynya; an opening which is flanked by large floes and therefore appears to be relatively stable is called a stable polynya. When frozen over, a polynya becomes an ice skylight from the point of view of the submariner. SPRI A Russian term meaning an area of open water, possibly containing some thin ice, within the ice pack. A polyn'ya is distinguished from a lead by being a broad opening rather than a long, narrow fracture. (Also called ice clearing.) Polyn'ya AMSglossary GCW |