The Arctic ocean

The Arctic Ocean is the smallest of the world's five oceans (after the Pacific Ocean, Atlantic Ocean, Indian Ocean, and the recently delimited Southern Ocean). The Northwest Passage (US and Canada) and Northern Sea Route (Norway and Russia) are two important seasonal waterways. A sparse network of air, ocean, river, and land routes circumscribes the Arctic Ocean.

Most of the Arctic Ocean is permanently covered with a vast floating raft of sea ice. Temperatures are low all year round, averaging -30°C in winter and sometimes dropping to -70°C. During the long winters, which last more than four month, the Sun never rises above the horizon.

The Arctic gets its name from arctos, the Greek word for "bear", because the Great Bear constellation is above the North Pole.

There are three kinds of sea ice in the Arctic:

• Polar ice

The polar ice is the raft of ice that never melts through. It may be as thin as 2 m in places in summer, but in winter it is up to 50 m thick.

• Pack ice

The pack ice forms around the edge of the polar ice and only freezes completely in winter. The ocean swell breaks and crushes the pack ice into chunky ice blocks and fantastic ice sculptures.

• Fast ice

Fast ice forms in winter between pack ice and the land around the Arctic Ocean. It gets its name because it is held fast to the shore. It can't move up and down with the ocean as the pack ice does.

The ocean's central surface is covered by a perennial drifting polar icepack that, on average, is about 3 meters thick, although pressure ridges may be three times that thickness; clockwise drift pattern in the Beaufort Gyral Stream, but nearly straight-line movement from the New Siberian Islands (Russia) to Denmark Strait (between Greenland and Iceland); the icepack is surrounded by open seas during the summer, but more than doubles in size during the winter and extends to the encircling landmasses; the ocean floor is about 50% continental shelf (highest percentage of any ocean) with the remainder a central basin interrupted by three submarine ridges (Alpha Cordillera, Nansen Cordillera, and Lomonosov Ridge)

Ports and harbors : Churchill (Canada), Murmansk (Russia), Prudhoe Bay (US)