The pack ice is the most common type of sea ice before the drift ice and consists of densely arranged ice floes, between which, however, there can also be smaller free water surfaces. 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 to 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 upward current on obstacles and different ocean currents, press ice mounds are also formed at the edges of two pack ice floes, which can reach a depth of 20 m. These can hinder the dispatch or even make it impossible. Loose pack ice fields are usually just an obstacle to larger ships, but can be destroyed with icebreakers. To prevent a ship from freezing, special channels - so-called Wuhnen - are knocked 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 St. Lawrence and the Baltic Sea, depending on the season. The pack ice boundary in the northern hemisphere is 80 degrees north latitude, but it is very variable. In spring, the pack ice border can advance locally to about 50 degrees north latitude.
Some polar bears also live here