The Arctic and Antarctic areas are very different. Unlike the Antarctic, which is a continent surrounded by oceans, the Arctic is an ocean surrounded by continents (Europe, Asia, and North America - including Greenland, the world's largest island).

The roughly circular Arctic Ocean is located entirely within the Arctic Circle and with an area of about 5,427,000 sq. miles / 14,055,000 sq. kilometers, it is the smallest of the world's oceans.

The central surface of the ocean is covered by a drifting polar ice cap, although the ice cover is shrinking by about 13,000 sq. miles / 33,800 sq. kilometers per year.

There is about 15% less ice than there was 20 years ago. In the 1950s, ice averaged 10 feet / 3 meters thick - now it averages less than 6 feet / 1.8 meters thick, although pressure ridges may push the ice to three times that thickness.

Walking across the ice may seem quite simple, but leads can open up without warning. Underneath that ice is a very deep ocean - the deepest spot is the Fram Basin at 4,665 meters / 15,300 feet, and that's a lot of icy cold water!

The ice-cap is surrounded by open seas during the summer, but it more than doubles in size during the winter and covers the entire ocean. This greatly restricts ocean travel, and the Northwest Passage (through Canada and above Alaska ) is not a practical shipping route. The Northern Sea Route (above Norway and Russia) is used regularly for shipping, but it must be kept open with icebreakers.

However, at the current rate of melting, the Northwest Passage could be basically ice-free all summer long in the not-too-distant future.