Arctic sea ice is usually 1 to 3 meters, or as much as 9 feet, thick. It grows during autumn and winter and shrinks in spring and summer. Scientists have monitored sea ice conditions for 50 years.
* Ice melting across globe at accelerating rate, NASA says
The disappearance of the ice in the past decade is astounding, climate scientists say.
"We've been seeing a retreat year after year," said Marika Holland, an oceanographer with the National Center for Atmospheric Research in Boulder, Colorado. "The sea ice loss we observed in the summer of 2007 was shocking."
Soon there may be no sea ice anywhere in the Arctic during some months of the year.
Although environmentalists are concerned by this melting trend, shipping and energy companies are salivating at the prospect of smaller ice caps, which makes Arctic drilling and commerce easier. Cargo ships may be able to travel from Asia to North America more cheaply and efficiently, for example.
In a showy technological display August 2, 2007, a Russian submarine planted an underwater flag 14,000 feet (4,200 meters) below the North Pole.
Russian scientists are keen on proving that the seabed below the North Pole is part of the Eurasian continental shelf, an area called the Lomonosov Ridge.
If that's the case, the region would be under Russian control
"Most of the estimated undiscovered resources are in areas with agreed-upon territorial boundaries," said Don Gautier, research geologist at the USGS.
"Exceptions are the East Barents Basins, where Russia and Norway are involved in bilateral discussions of the offshore boundary. Another exception is the Alaska./Canada boundary offshore, which is also subject to bilateral discussions between U.S. and Canada," he said.
"The Russians have got a half-dozen icebreakers. Americans have a pair of icebreakers, but they are old and worn out," Pike said.
And of course, much of countries' access to the Arctic will come down to money.
"Building a ship to operate in a foot of ice is no big deal. Building an icebreaker that can get through 2 yards of ice, now you're talking serious icebreaking. The Russians can get through 2 yards of ice without breaking a sweat," Pike said.
Ultimately, questions about what is drilled for in the Arctic, and by whom, will depend on the global economy. Recovering oil from a forbidding frozen wilderness makes sense when it's selling for $150 a barrel, but not so when it is at $40 a barrel.