Formation of Polynyas

To create a polynya, one has to remove sea ice from a region and/or prevent it from forming.
 
The first of these mechanisms (removal of sea ice) is the primary way that polynyas form close to the coastline. Strong surface winds blow the ice off-shore, opening up the surface waters and allowing the formation of more sea ice, indeed coastal polynyas have been likened to 'sea ice factories'.
 
The second of these mechanisms (prevention of sea ice formation) is perhaps more interesting. How can one keep the sea surface temperature above freezing thereby preventing the formation of sea ice? Remember, we are talking about the depth of the Antarctic winter: the atmosphere is very cold and there is little or no sunlight! The answer is the deep ocean. There are regions where the water at some depth below the surface is actually warmer than the water at the surface. It is also saltier and denser and therefore not easily brought to the surface. However, if the surface waters can be cooled and made more salty (by losing heat and moisture to the atmosphere) there is the possibility that the warm deep water can be exchanged with colder surface waters through a process known as convection. This process is thought to be the mechanism by which open ocean polynyas form and are maintained.
 
The presence of open ocean polynyas are therefore important as they signal that ocean is undergoing convective overturning.