The Weddell Polynya, or Weddell Sea Polynya, is a
polynya or irregular area of open water surrounded by sea ice in the
Weddell Sea
The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Mar ...
of the
Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-smal ...
off
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest co ...
and near the
Maud Rise. The formation of the polynya exposes relatively warmer ocean waters (at surface freezing temperatures of -1.9°C) to a cold atmosphere, leading to a large exchange of heat which drives deep convection in the ocean, often reaching depths of a 1,000 to 2,000 meters!
Occurrences
The size of New Zealand, it re-occurred each winter between 1974 and 1976. These were the first three austral winters observed by the Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR). From 1976 to 2015 this polynya was rarely observed. The polynya reoccurred in 2016, and has since appeared in 2017. The 2010s occurrence has been smaller than the 1970s occurrence, being about the size of Maine in 2017, or roughly .
Since the 1970s, the polar Southern Ocean south of the
Antarctic Circumpolar Current has freshened and stratified, likely a result of anthropogenic
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
. Such stratification may be responsible for suppressing the return of the Weddell Sea polynya.
More recently, it was found that intense cyclones occurring over the ice pack, far south from the ice edge, were at the origin of the reoccurrence of the Weddell or Maud Rise Polynya in austral winter 2017. In certain winter months, the general atmospheric circulation around Antarctica exhibits a strong zonal wave 3 pattern which favor the development of polar cyclones closer to the coast i.e. over preconditioned oceanographic areas for polynya formation such as the Weddell Polynya in the Lazarev Sea and the Cosmonaut polynya in the Cosmonaut Sea around Antarctica.
Other Antarctic polynyas
The presence of polynyas in
McMurdo Sound
McMurdo Sound is a sound in Antarctica. It is the southernmost navigable body of water in the world, and is about from the South Pole.
Captain James Clark Ross discovered the sound in February 1841, and named it after Lt. Archibald McMurdo of ...
provides an ice-free area where penguins can feed, so is important for the survival of the
Cape Royds penguin colony.
See also
*
Polar Cyclones
*
Coriolis force
*
Ekman layer
*
Ekman number
The Ekman number (Ek) is a dimensionless number used in fluid dynamics to describe the ratio of viscous forces to Coriolis forces. It is frequently used in describing geophysical phenomena in the oceans and atmosphere in order to characterise the r ...
*
Ekman spiral
*
Ekman transport
*
Ekman velocity
*
Fridtjof Nansen
*
Nansen's Fram expedition
*
Upwelling
*
Vagn Walfrid Ekman
References
Geography of the Southern Ocean
Bodies of water of the Southern Ocean
{{Glaciology-stub