Why are some icebergs green in Antarctica? Researchers think they've solved century-old mystery

The stunning sight of emerald green-colored icebergs in Antarctica has been documented for more than a century — in literature and beyond.

For decades, scientists have argued about the cause behind the bizarre phenomenon and debated why the green-hued ice chunks aren't the typical blue or white color. But a recent discovery from a 2016 research trip to East Antarctica’s Amery Ice Shelf may provide the final clue they've been waiting for.

In a new study published in the Journal of Geophysical Research: Oceans, researchers found marine ice varies in color due to the "abundance of foreign constituents in the seawater," particularly iron-oxide materials. They came to this conclusion after scientists detected "large concentrations of iron" in the Amery Ice Shelf.

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"Previously, dissolved organic carbon (DOC) had been proposed to be responsible for the green color," authors Stephen Warren, Collin Roesler, Richard Brandt and Mark Curran explained in the paper. "Subsequent measurements of low DOC values in green icebergs, together with the recent finding of large concentrations of iron in marine ice from the Amery Ice Shelf, suggest that the color of green icebergs is caused more by iron‐oxide minerals than by DOC."

Icebergs are typically blue or white because they contain ice bubbles and snow particles that bend and scatter light.

Warren, a professor at the University of Washington and glaciologist who has been studying green icebergs for decades, said researchers used to believe seawater freezing onto the base of icebergs — combined with the icebergs' already blueish shade — contributed to the green color.

But they have since concluded that iron-oxide rich minerals, also referred to as "glacial flour," that collects at the bottom of some ice shelves is reddish yellow. When a chunk of ice breaks off, those two colors combined with the already blueish hue from ice bubbles contribute to the green color seen after the sun reflects off the iceberg.

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"The marine‐ice part of such icebergs is clear, dark, and often green in color, because red or yellow particles from the seawater, in combination with the blue of ice, can shift the color to green," the researchers further explained.

Ted Scambos, a senior research scientist at the National Snow and Ice Data Center who did not contribute to the research, told Mashable the explanation makes "perfect sense."

"When you put it in a red-absorbing material, you're going to get green light coming back out," he told the publication.

If our theory proves correct, green icebergs could be more important than scientists thought."

— Stephen Warren, Collin Roesler, Richard Brandt and Mark Curran

Warren plans to collect more samples to support their latest theory.

“Iron is a key nutrient for phytoplankton, microscopic plants that form the base of the marine food web. But iron is scarce in many areas of the ocean,” the researchers told Science News on Tuesday. “If experiments prove our theory right, it would mean green icebergs are ferrying precious iron from Antarctica’s mainland to the open sea when they break off, providing this key nutrient to the organisms that support nearly all marine life.”

“We now propose to sample icebergs of different colors for their iron content and light-reflecting properties. If our theory proves correct, green icebergs could be more important than scientists thought," the team added.