Pack ice
Pack ice is the most common type of sea ice before drift ice and consists of densely arranged ice floes , between which, however, smaller free water surfaces (whereby the free water surfaces are not to be confused with larger polynjas ) can exist. There is no precise definition of when a sea ice cover is so dense that it can be considered pack ice. Typically, however, a sea cover of 80–100 percent is assumed. The ice is then so dense that it represents an obstacle to shipping and enables long migrations of the Arctic land fauna .
The white ice armor is about 3.5 m thick. As a result of the flowing up against obstacles and different ocean currents , press ice mounds also form at the borders of two pack ice floes , which can reach a depth of 20 m. These can hinder shipping or even make it impossible. Loose pack ice fields are usually only a hindrance for larger ships, but can be destroyed with icebreakers . To prevent a ship from freezing, special channels - so-called Wuhnen - are cut into the ice so that the ship is not crushed by the ice.
In the Arctic, the pack ice covers about 3 to 15 million square kilometers in the Arctic Ocean , the directly adjacent marginal seas of the Atlantic and Pacific as well as the Sea of Okhotsk , the Gulf of Saint Lawrence and the Baltic Sea , depending on the season . The pack ice border in the northern hemisphere is 80 degrees north latitude, but it is very variable. In spring, the pack ice border can advance locally to around 50 degrees north latitude.
In the southern Antarctic Ocean , pack ice can occur south of the 60th degree south latitude, with 1 to 16 million square kilometers of sea surface covered depending on the season.
