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7 March, 2019 00:00 00 AM
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Why are some icebergs green?

NEWSWEEK, New York
Why are some icebergs green?

For over a century, sailors and explorers have reported seeing bizarre emerald green icebergs around Antarctica. Their unusual color has long perplexed researchers, and they have been scrutinized by scientists for decades.

Now Stephen Warren, a glaciologist at the University of Washington, and his colleagues may have finally solved the mystery. In a paper published in Journal of Geophysical Research: Oceans, researchers found the icebergs are green because of iron oxides from rock dust found on Antarctica’s mainland.

“Green icebergs occur only in the Antarctic Ocean, so they would not have been seen before Cook’s expedition in 1774, if then,” Warren told Newsweek. “Coleridge’s poem The Rime of the Ancient Mariner mentions ‘ice, mast high, came floating by, as green as emerald.’ Maybe that was just poetic imagination. Green icebergs entered the scientific literature in 1921 with Drygalski’s report of the German expedition of 1903, and since then there have been occasional reports of sightings by ship captains.”

Normally, icebergs form when they break away from glaciers and ice shelves. This glacier ice is formed of layers of snow that builds up over time and solidifies, meaning it has air pockets that reflect light. This ice appears blue because it absorbs more red light than blue.

However, in Antarctica some icebergs have a layer of marine ice, which is ocean water that has frozen to the underside of the ice shelf. Because it lacks air pockets, marine ice appears clearer and darker than normal ice. Warren said about one percent of icebergs contain visible marine ice.

Initially, scientists thought the green icebergs were made from marine ice rather than glacier ice. The color was believed to be the result of dead marine plants and animals that had become trapped when the water froze—as the organic material broke down, it turned into dissolved organic carbon, which has a yellow color. When the blue glacier ice mixed with the yellow marine ice, theory hypothesized, a green color would be produced.

However, in the 1990s, Warren discovered this could not be the case. During an expedition, his team found that green ice contained the same amount of organic material as blue—meaning something else must be responsible for the emerald coloring.

 

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Editor : M. Shamsur Rahman

Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.

Editor : M. Shamsur Rahman
Published by the Editor on behalf of Independent Publications Limited at Media Printers, 446/H, Tejgaon I/A, Dhaka-1215.
Editorial, News & Commercial Offices : Beximco Media Complex, 149-150 Tejgaon I/A, Dhaka-1208, Bangladesh. GPO Box No. 934, Dhaka-1000.

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