The Shawinigan and the Glace Bay docked in Churchill on Sunday, marking a return by the navy to the remote port on the shores of the Hudson Bay for the first time in 30 years. Meanwhile, a third frigate, the HMCS Fredericton, was travelling towards eastern Arctic waters.

The Fredericton is ostensibly there to impose fishing regulations but is expected to pass close to a tiny island that has become the subject of diplomatic head-butting between Canada and Denmark. Both claim the barren rock, named Hans Island.

For years, Canada has taken its control of the vast northern region mostly for granted. But with the melting of polar ice providing access for shipping, the government is anxious about possible territorial rivalries with Norway, Russia and the United States as well as Denmark.

The melting ice, attributed to global warming, could even open the legendary North-west Passage, linking the Atlantic and the Pacific, to shipping. Canada and Russia are at odds over areas of the continental shelf in the region, with its potentially important mineral and oil deposits.

Meanwhile, the United States wants the Passage to be under international, not Canadian, control. There are also fears of clashes with the US over riches beneath the Beaufort Sea which extends northwards from the coasts of both Canada and Alaska.

Canada admits that the sudden burst of naval activity is no coincidence. "This is a demonstration of Canada's will to exercise sovereignty over our own back yard," Commodore Bob Blakely, of the Royal Canadian Navy, told reporters in Churchill at the weekend.

"The sea is a highway that's open to everyone. We will allow everybody passage as long as they ask for our consent and comply with our rules: Use our resources wisely and don't pollute the fragile northern ecosystem. It's like having a path behind your house. Nobody minds the neighbours walking along. Just don't dump your garbage there and don't take my vegetables out of the garden," he said.

The row with Denmark dates back to 1973 when both countries attempted to draw the boundary between north-eastern Greenland and Ellesmere Island that belongs to Canada. They failed to resolve ownership of Hans Island, a barren rock that measures about half a square mile. In 1984, a Danish minister landed on Hans Island and planted a Danish flag with a bottle of brandy buried beneath it. Canadian soldiers returned earlier this year with a Canadian flag and bottle of Canadian whiskey. Then last month the Canadian Defence Minister Bill Graham set foot on Hans Island.

"We consider Hans Island to be part of Danish territory and will therefore hand over a complaint about the Canadian minister's unannounced visit," the head of the Department of International Public Law at Denmark's Foreign Ministry, Peter Taksoe-Jensen, said at the time.

Both countries have since agreed to discuss the dispute at the United Nations next month.

But the wider issue of protecting its northern edges seems to preoccupy Canada. Ottawa is to launch a satellite to orbit above the Arctic to monitor shipping. There are also plans to invest in a new road up the MacKenzie river valley all the way to the frozen port of Tuktoyaktuk with a view to future development of the region's natural resources.