The ice cracks and falls to the side of the ship, a Canadian coast guard vessel named the CCGS Amundsen, turning up a blue underside. And the ship continues on its course, west of Cornwallis Island in the Canadian Arctic.

Post journalist Alice Li and I boarded the Amundsen on Saturday to accompany its scientific crew on a research voyage through the Northwest Passage.

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These waters and the ice that covers them claimed the lives of many European explorers in the past.

Now scientists are using a sophisticated multibeam sonar device to map the seafloor beneath the ship in high resolution, and pulling up cores of mud to learn about the geologic history of the area.

The knowledge they obtain will be crucial as more vessels venture into the area, spurred by climate change and the dramatic reduction in the extent of sea ice.

We will be accompanying these researchers, part of the ArcticNet research consortium based at Université Laval in Quebec City, to see what they discover about seas and subsea landscapes that are still very poorly understood.

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The increase in vessel traffic raises concerns about safety and possible environmental damage. Scientists need to know more about the passage to help make it safe, even as they must also study its ecology and fisheries to determine the consequences if humans manage to despoil it.

We are making the journey in the context of 500 years of history.

Starting in the late 1500s with Martin Frobisher, the quest to discover and safely transit a twisting path through the Northwest Passage has fueled commercial dreams even as it claimed many lives and wrecked many ships in a saga of mutiny, strandings and disease.

In 1846, the British officer Sir John Franklin tried to sail the route that the CCGS Amundsen plans to take in the coming days. Franklin was frozen near today’s Queen Maud Gulf, whose shallow waters lie nearly equidistant between the Pacific and Atlantic oceans. The expedition lost over 100 men, and Canadian government archaeologists only recently discovered the wrecks, the Erebus and the Terror.

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It wasn’t until the early years of the 20th century that Norwegian explorer Roald Amundsen completed the first successful passage to the Pacific, over three years, wintering for three seasons as he went.

But now as the climate warms and Arctic sea ice levels plummet, passages are increasing.

Data compiled by Robert Headland and colleagues of the Scott Polar Research Institute at the University of Cambridge show 254 transits of seven separate possible routes between Amundsen’s passage and the end of last year, with a sharp increase in recent years.

There were 16 crossings last year, including the Crystal Serenity, a massive cruise ship carrying some 1,000 passengers that was guided by its own icebreaker. The cruise ship will be back later this year.

For the most part, the passage remains what navigation experts call “destinational”: people who want to see the place and be there such as tourists on cruises, owners of private yachts and smaller boats.

The original goal of seeking out the Northwest Passage to find a shorter trade route between the Atlantic and Pacific oceans is still not fully realized.

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Ice conditions are still unpredictable, which is a major problem. “Yes the general trend is down, it’s declining, but the thing to pay attention to is the intraseasonal variability. There’s massive swings,” said David Jackson, director of the Canadian Ice Service.

Ship traffic will still be limited to summer months for the foreseeable future. And there’s just not much infrastructure to allow ships to dock in ports or to provide rescue if trouble arises.

But few doubt the overall trend: More open water, beginning earlier in the year and lasting later into the start of winter. And the route is getting more traffic — although there is skepticism about whether large shipping companies will be using the route any time soon. That’s why this mission — and charting the passage — is so important.