Despite predictions from a top U.S. polar institute that the Arctic Ocean's overall ice cover is headed for another "extreme" meltdown by mid-September, the Environment Canada agency monitoring our northern waters says an unusual combination of factors is making navigation more difficult in the Northwest Passage this year after two straight summers of virtually clear sailing.

In both the wider, deep-water northern corridor and the narrower, shallower southern branches of the passage, the Canadian Ice Service says pockets of more extensive winter freezing and concentrations of thicker, older ice at several key "choke points" are complicating ship travel.

The fabled trans-Arctic sea route, zealously sought by European explorers in centuries past as a shortcut to Asia, is increasingly seen in today's era of rapidly retreating sea ice as a potential highway to resource riches and Arctic tourist destinations.

A record number of vessels passed through Canada's Arctic islands last year, and experts have been predicting a steady rise in ship traffic in both the Northwest Passage and the Northern Sea Route, which connects Europe to eastern Asia along Russia's Arctic coast.

The northern route of the Northwest Passage is called the Parry Channel, a deep, wide and relatively direct path between the Atlantic and Pacific oceans that runs through Canada's Arctic archipelago between northern Baffin Island in the east and northern Banks Island in the west.

That route connects Lancaster Sound, Barrow Strait, Viscount Melville Sound and, finally, McClure Strait at the western outlet to the northern Beaufort Sea.

The southern branches of the Northwest Passage follow the northern route through Lancaster Sound and Barrow Strait before turning south on either side of Prince of Wales Island, through Peel Sound or McClintock Channel toward mainland Northwest Territories and a coastal route exiting at Amundsen Gulf and the southern Beaufort.

While the northern route offers a potentially faster, shorter path through deeper waters, its ice cover is typically thicker and last longer into the summer.

The southern routes are typically clearer of heavy ice, but shallower waters and the circuitous path present other challenges for ships making trans-Arctic voyages.

"In the southern route," Canadian Ice Service officials told Canwest News Service, the agency "has observed more ice coverage than normal. This is partly due to the fact that the ice in the Amundsen Gulf consolidated this past winter, which is something it didn't do in 2007 and 2008."

In the central part of the passage where the northern and southern routes merge amid narrowings around Prince of Wales Island, the CIS has observed "greater than normal concentrations of thicker, multi-year ice. This is the result of an increased flow of older ice from the Beaufort Sea into the Canadian Arctic archipelago last year."

The result, the agency said, is that ice conditions "are delaying any potential navigability of the Northwest Passage this year. This is opposite to what Environment Canada observed in the last week of July in 2007 and 2008."

While Canada's trans-Arctic sea route remains clogged with ice, the U.S. National Snow and Ice Data Center is predicting another near-record meltdown by the end of this year's summer thaw.

The unprecedented 2007 shrinkage of polar ice cover to just 4.13 million square kilometres - nearly matched last year when only a 4.52-million-sq.-km. expanse of ice was left by mid-September - has led many forecasters to envision a virtually ice-free Arctic

The Colorado-based NSIDC's daily tracking of Arctic ice extent shows this year's melt trending only slightly behind the record-setting 2007 rate.

"During the first half of July, Arctic sea ice extent declined more quickly than in 2008, but not as fast as in 2007," the Colorado-based NSIDC states in its latest report. "International sea ice researchers expect another low September minimum ice extent, but they do not yet know if it will fall below the 2007 record."

Scientists believe the ongoing retreat is being driven by several factors, including rising global temperatures associated with human-induced climate change, and the associated breakup and loss of thicker, multi-year year ice that is being replaced only seasonally by a thin layer of winter ice that disappears quickly each summer.

Earlier this summer, scientists with NASA and the U.S. National Oceanic and Atmospheric Administration warned that the unprecedented thinning of Arctic sea ice - a phenomenon not always evident in satellite images showing the shrinking area of the polar cap - could soon lead to largely ice-free summers throughout the region.

Source: Canwest News Service