A decades-long scientific mystery may have finally been solved. Some Antarctic icebergs are an odd emerald green color instead of the normal blue tinge and scientists have suggested a new theory as to why they look that way.
Ice absorbs more red light than blue light and that’s why they appear as a blue color. While most of them look blue or white while they are in the seawater, many people over the years have seen these oddly colored icebergs. Even sailors and explorers from the early 1900s have reported witnessing strange colored green icebergs around Antarctica.
While green icebergs have captured the curiosity of scientists for several decades, glaciologists conducted new studies which lead them to believe that iron oxides that’s in rock dust from Antarctica’s mainland is what’s turning the icebergs a green color. Australian researchers found huge amounts of iron in East Antarctica’s Amery Ice Shelf and that’s how the theory got started.
Interestingly, iron is a very important nutrient for phytoplankton which is a microscopic plant that’s at the base of the marine food chain. While iron is very limited in quite a few areas of the ocean, if this new discovery of iron in some icebergs proves to be true, it would be an extremely important benefit for marine life.
According to Stephen Warren, who is a glaciologist at the University of Washington, “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,” adding, We always thought green icebergs were just an exotic curiosity, but now we think they may actually be important.”
Icebergs break off of glaciers and ice shelves that extend out into the sea. Normal glacier ice is created when several layers of snow build up and eventually harden up, meaning that it has air pockets that light reflects off of. However, some icebergs in Antarctica contain a layer of marine ice which is water from the ocean that has frozen to the bottom of an overhanging ice shelf. Since marine ice doesn’t have any air pockets that reflect light, it is darker and much clearer than glacier ice. When Warren and his colleagues studied the green icebergs, they noticed that the green areas were in fact made up of marine ice instead of glacier ice.
Iron oxides that are found in soil, common rust, and rocks typically have warm, earthy colors such as yellow, orange, brown, and red. That’s why Warren was thinking that the iron oxides in the marine ice were turning the blue ice into a green color.
When glaciers move over bedrock, the rocks end up grinding into a very fine powder called glacier flour that ends up going into the ocean. The pieces of rock dust could then become part of the marine ice if it gets trapped under an ice shelf.
Warren, along with iron researchers from Australia are now planning to sample different colored icebergs in order to find out exactly how much iron they contain as well as how much light they reflect. If their theory is proven, that would be a huge discovery in regards to the study of icebergs, especially since iron is such an important and beneficial nutrient to marine life.