Chapter 4. Moving Ice Edge

(The narrator of this story is a Canada Goose named Tutangiaq, unless specified otherwise)

When I fly far enough north I often encounter vast stretches of Arctic sea ice, where the water has literally frozen from the extended cold weather.

During the summer months, the sea ice covers an average of 7,000,000 sq km, but grows to around 14,000,000 sq km during the winter. By comparison, the entire United States is just over 9,000,000 square km. (interactivity 4.1)

Over the years the thickness and extent of seasonal ice cover has decreased. Scientists predict that increased melting of ice will result in a rapid warm-up of the polar regions. I wonder how this Arctic warming is affecting my pinniped friends, especially walruses.

(Walrus narrates). You're right Tutangiaq. We walruses use sea ice as an important place to rest, breed, and molt. The ice breakup has been occurring earlier in the year and its edge receding further now than even a decade ago. Look at these satellite images which preserve a record of how the sea ice edge has changed over the years. Of course, we need data for many more years to establish a reliable trend. (interactivity 4.2)

(Walrus narrates). Did you ever wonder how these satellite images reveal changes in sea ice? Even though water and ice have the same chemical formula (H2O) they have a different chemical structure and physical properties. Ice has a crystalline structure that reflects most of the visible energy that falls on it, making ice appear bright in satellite images from the visible spectrum. Clear water on the other hand tends to absorb most of the visible energy that strikes it, making water appear relatively darker than ice on the same image. This contrast in the behavior of water and ice can be seen as variations in tone (gray shades) on a satellite image.

(Walrus narrates). As you may know, we pinnipeds are adapted for an aquatic environment and are most vulnerable to predators out of the water. For us, sea ice is the safest ground with minimum risks. From there we like to dive down to the continental shelf where we feed. (more information 4.1). The farther the ice edge recedes from the continental shelf in the summer and the longer that lasts, the farther we have to travel to eat. Some scientists believe that the sea ice edge could be receding because of gradual global warming.

That's terrible to hear! I know that scientists are working hard to study the global environment. Some believe that we are seeing global warming. Hopefully, we can all together to preserve our environment and ensure that we do not contribute to global warming.

Oh now I am too cold! Maybe it's time for me to rejoin my migrating family.

More information and interactivity in Chapter 4

More information 4.1:
Regions of the Ocean: The ocean can be divided into several regions. (Figure showing the sea with sea ice. Also shown are the coast, which extends to the continental shelf, continental slope, continental rise and the deep sea bed).

Interactivity 4.1:
Seasonal variation in the extent of Arctic Sea Ice: Graphics showing Arctic Sea Ice. The graphic has 4 tabs on top. Clicking on these tabs, the main graphic changes to show the Arctic sea ice extent in March 1985, June 1985, September 1985, and December 1985.

Interactivity 4.2:
Variation in the extent of Arctic Sea Ice from 1972 through 1993: Graphics showing Arctic Sea Ice. The graphic has 8 tabs on the left. Clicking on these tabs, the main graphic changes to show the Arctic sea ice extent in the third week of September for the years 1972, 1975, 1978, 1981, 1984, 1987, 1990 and 1993.

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