For centuries, significant resources have been expended in search of the Northwest Passage, or as Pierre Berton once called it; the “Arctic Grail.” Franklin, Davis, Ray, Baffin, Amendment, Blot, Monk, and Perry are just a few of the names that have gone down in history for their quest for the shortest route from Europe to Asia. It was sea ice that foiled the best laid routes and provided the suspense and intrigue we are all now familiar with. The waxing and waning of sea ice movement in the northern hemisphere has long created seasons when a ship could sail easily through Baffin Bay, while in other years “rivers” of ice flushed down from the Lincoln Sea towards the Labrador coast. The high variability experienced by these explorers was the norm of the day.
However, things do appear to be changing, and these trends are cause for concern. In recent years, scientists, through the media, have been informing the public about developments concerning sea ice in our northern hemisphere. Articles such as “As Polar Ice Turns to Water, Dreams of Treasure Abound” (the New York Times) recall the economic forces at play several centuries ago, while making a scientifically based prediction that the Arctic ocean may become the next, and likely one of the last, of our great oceans to exploit, conserve and protect.
Sea ice occurs at both poles as a result of large scale variations in solar insolation (incoming solar radiation or the sun’s rays) and changes in oceanic and atmospheric circulation driven by the seasonal global balance in net energy. An oscillating planetary energy balance is established with net positive surplus at the equator and net loss at the poles. Seasonal modulation of this general pattern is driven by the fact that the planet’s axis of rotation is 23.4° offset from the perpendicular. This means that solar insolation is much larger at the equator than at the poles, and this sets up (at least in a first order fashion) the seasons that create polar sea ice. It also results in an overall planetary energy balance with opposing signs at each pole, which helps to establish a planetary-wide circulation of heat from the equator poleward and vice-versa.
In the Arctic, sea ice forms annually throughout most of the area north of the Arctic Circle whenever the ocean dips below -1.8°C. Maximum volume of ice occurs around the end of March, with an area of about 14 million km2. Perennial ice occurs throughout the Canada and Arctic basins in the summer, and annual ice grows over the shallow continental shelves northward to meet the southern advance of the perennial pack. Reduction in this maximal extent occurs throughout the summer season until a minimum of about 7 million km2 is reached, sometime around the end of September.
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David Barber is associate dean (research); Clayton H. Riddell Faculty of Environment, Earth, and Resources; Canada Research Chair in Arctic System Science; and director, Centre for Earth Observation Science, University of Manitoba.
Louis Fortier is a professor of biology and Canada Research Chair on the Response of Marine Arctic Ecosystems to Climate Change, ArcticNet, Department of Biology, Université Laval.
Michael Byers is Canada Research Chair in Global Politics and International Law, University of British Columbia.