Antarctic Sea Ice and Polynyas

Kent Moore , Department of Physics ,University of Toronto,

Keith Alverson , PAGES, International Project Office,

and

Ian Renfrew , British Antarctic Survey

 

July 22 1999

What's new:

jump to current status of the 1999 Cosmonaut Sea Polynya

jump to high resolution infra-red satellite images of the 1999 Cosmonaut Sea Polynya

jump to time series of embayment/polynya area during July 1999

jump to breakup of land fast ice off Syowa

 
The waxing and waning of sea ice cover off Antarctica is one of the most striking examples of the dramatic transitions in our physical environment that is brought about by the earth's seasonal cycle. At its minimum in February, the areal extent of the ice cover is approximately 3.5 million square kilometers. Many sections of the Antarctic coastline are ice free. At its maximum in September, the areal extent is approximately 19 million square kilometers and the entire continent is surrounded by a thick ring of sea ice. The seasonal change in sea cover in Antarctica is much larger that than that in the Arctic where the presence of land surrounding the Arctic Ocean limits the growth of ice.
 
In the fall and winter within the ice pack, large areas of open water known as polynyas are sometimes observed. Polynyas are of great biological and physical interest. These are areas where sea mammals have convenient access to the atmosphere and where birds have easy access to the ocean. These are also regions where the atmosphere and ocean can interact without the usual insulating intermediary -sea ice. In polynyas, the sea surface temperature is, by definition, above freezing (approximately -1.8 deg C for sea water). In the depths of the Antarctic winter, surface temperatures over the ice pack are perhaps 20 or 30 degrees colder. In such a situation, one would expect a vigorous transfer of heat and moisture from the relatively warm ocean to the very cold and dry atmosphere. This results in a warming and moistening of the atmosphere and a cooling and salinization of the ocean. This often results in the formation of interesting clouds over the polynya .
 
There are two basic types of polynyas and two different formation mechanisms. Those that form close to the coastline are called coastal polynyas and those that develop deep in the ice pack far from shore are called open ocean polynyas.
 
Our ability to monitor ice conditions deep in the Antarctic ice pack has only existed since 1972 when NASA's Nimbus 5 was launched with the first spaceborne passive microwave radiometer- an instrument able to distinguish between open water and sea ice. The successors to this remarkable instrument are used to provide daily global retreivals of sea ice concentration and are used on this site to monitor real time changes in the sea ice cover off Antarctica.

The most dramatic example of an open ocean polynya occurred during the mid-1970's when a large region of the Weddell Sea remained ice free during each of three winters.
 
We are currently monitoring anomalous sea ice conditions in the Cosmonaut Sea and have observed the formation an open ocean polynya.