Sea ice#Fast ice versus drift .28or pack.29 ice
Pack ice is still front of the drift, the most common type of sea ice and consists of densely packed ice floes between which and also smaller free water surfaces ( the free water surfaces are not to be confused with the larger polynyas ) can exist. A precise definition of when a Meereseisbedeckung is so dense that it can be regarded as sea ice does not exist. Typically, however, assume a marine coverage of 80-100 percent. The ice is then so dense that it is an obstacle for navigation and allows wide migrations of the arctic terrestrial fauna.
The white ice cap is powerful to about 3.5 m. By Aufströmen obstacles and by different ocean currents are formed at the boundaries of two ice floes but also hummocks, which can range from 20 m to a depth. This can hinder the shipping or even impossible. Loose pack ice fields form a disability, but can be destroyed with icebreakers usually only for larger ships. Against the freezing of a ship are special channels - so-called Wuhnen - beaten into the ice to keep the ship from being crushed by the ice.
In the Arctic, the sea ice covered depending on the season about 3 to 15 million square kilometers of the Arctic Ocean, immediately adjacent to the marginal seas of the Atlantic and the Pacific and the Sea of Okhotsk, the St. Lawrence Gulf and the Baltic Sea. The pack ice in the northern hemisphere is at the 80th degree of north latitude, however, is highly variable. In spring, the pack ice may locally move forward to about the 50th degree of north latitude.
In the southern Antarctic Ocean pack ice may south of 60 degrees south latitude occur, with 1 to 16 million square kilometers of ocean surface can be covered depending on the season.