leads and polynyas are areas of open water that occur within sea ice expanses even though air temperatures are below freezing, and provide a direct interaction between the ocean and the atmosphere, which is important for the wildlife. leads are narrow and linear – they vary in width from meter to km scale. during the winter, the water in leads quickly freezes up. they are also used for navigation purposes – even when refrozen, the ice in leads is thinner, allowing icebreakers access to an easier sail path, and submarines to surface more easily. polynyas are more uniform in size than leads and are also larger – two types are recognized: 1) "sensible-heat polynyas", caused by the upwelling of warmer water and 2) "latent-heat polynyas", resulting from persistent winds from the coastline.