We are used to the idea of white and blue icebergs, but since the 1900s, explorers and sailors have seen green icebergs floating around in the Antarctic landscape. This color has been puzzling scientists for years, and now they have come up with a plausible explanation.
A team of glaciologists proposes that these green icebergs contain iron oxides that are carried from the mainland in Antarctica. If this research is correct, it means that the green icebergs have frozen crucial nutrients that can support almost all marine life.
"It's like taking a package to the post office. The iceberg can deliver this iron out into the ocean far away, and then melt and deliver it to the phytoplankton that can use it as a nutrient," says Stephen Warren, the paper's lead author and a glaciologist from the University of Washington.
"We always thought green icebergs were just an exotic curiosity, but now we think they may actually be important."
Warren has been studying this phenomenon for 30 years and he took samples in 1988 near the Amery Ice Shelf of East Antarctica.
"When we climbed up on that iceberg, the most amazing thing was actually not the color but rather the clarity," Warren said. "This ice had no bubbles. It was obvious that it was not ordinary glacier ice."
Most of the icebergs that form in the Antarctic are in shades of white or blue. The bluer the ice, the older it is. The compression from the accumulating layers of snow pushes the air bubbles out of the ice, thus reducing the scattering of white light.
The compressed ice absorbs the light spectrum except for blue icebergs, creating the green color that is seen in some icebergs and glaciers.
The researchers will need to get more samples and conduct further studies to analyze the minerals found in the green colored icebergs. This is to make sure that their theory about the green icebergs being rich in iron is correct. If they are right, the green icebergs can be an important transport for iron to other locations in the Southern Ocean.
"We always thought green icebergs were just an exotic curiosity," Warren said, "but now we think they may actually be important."
Iron is one of the nutrients that are needed for the growth of phytoplankton, but the supply is short in the southern seas. The green icebergs can carry the iron that it contains far from shore and it can help to enable marine life in areas where it normally wouldn't.
