Ice melt in Canada's Great North already allows boat traffic in the Northwest Passage, long the definition of a difficult route between the Atlantic and Pacific through the Arctic, which cuts the sea travel distance between Europe and Asia by a third.

This tortuous route however should be open almost half of the year by around 2035. That could foster cooperation, or turbocharge turf squabbles between Canada and the United States, whose claim on the Arctic is its state of Alaska.

There is already a history of rivalry between the two generally friendly neighbors over the passage.

The United States considers the passage international waters free to navigation.

But Canada rejects the argument, and has always defended tooth-and-nail its "sovereignty" over the passage and what it sees as its territorial waters.

"The Northwest Passage issue is not a Canada-US issue; the European Union, Russia and others have the same concerns as we have," Evan Bloom, deputy director for polar affairs at the US State Department, told AFP.

The United States and Canada in the 1980s signed an agreement allowing US ice-breaker ships through what Ottawa maintains are Canadian waters.

"There are problems with this agreement, because no reference was made to submarines or commercial craft," said Joel Plouffe, a researcher at the University of Quebec at Montreal who recently organized a discussion in Montreal on growing US interest in the Arctic.

Mead Treadwell, chairman of the US Arctic Research Commission, says the current agreement is not enough.

"We've promised not to send icebreakers without consultation first. (But) if you stop there, then you are not addressing the real issue, which is, some third nation may sail through and leave oil on both our soils," he said.

In the future, the Northwest Passage could become an increasingly busy commercial or cruise route, as traffic grows alongside interest in North American Arctic mining, oil and natural gas resources.

The biggest US oil field is at Prudhoe Bay, Alaska, and a huge natural gas project is planned for Canada's Northwest Territories, which could end up boosting traffic in the area.

And that is without factoring in development of what Treadwell noted is "the largest (proven) natural gas field in North America, and not yet developed."

Canada and the United States now need to agree on the precise demarcation of their border in the area, and on a formula for resource sharing and burden-sharing, such as patrolling the waters for security reasons, researchers say.

"There is no way the US wants the (passage to) become free for Pyongyang to deliver weapons" to another country, said Michael Byers, an international relations expert at the University of British Columbia.

Canadian forces are wrapping up an operation in the Northwest Territories to affirm Canadian sovereignty in the north and counter a simulated terrorist threat to oil production and transport infrastructure.

Byers predicted that potential for terror strikes, environmental disasters and illegal migration in this vast no-man's land ultimately will lead the United States to recognize Canadian sovereignty in these waters perhaps in exchange for guaranteed access for US ships without having to request permission from Ottawa.

"This is an open back door," Byers said.

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