Glaciologists might have unlocked the secret behind the emerald green tint of icebergs that drift around certain parts of Antarctica.
A new study suggests that the iron oxide in rock dust from the mainland is responsible for the unusual color. If proven true, the theory provides an answer to a mystery that has puzzled scientists for over a century.
Uncovering The Secret Of Green Iceberg
The researchers came into the conclusion after discovering large amounts of iron in East Antarctica's Amery Ice Shelf. Stephen Warren, a glaciologist from the University of Washington and the lead author of the new study published in the Journal of Geophysical Research: Oceans, started investigating the mystery of green icebergs in 1988 when he took home a sample from one to study.
Upon analysis, Warren found that the green iceberg is not typical glacier ice. It was marine ice. Glacier ice is formed when layers upon layers of snow solidify over time. However, marine ice is created when ocean water freezes to the underside of an overhanging ice shelf.
Warren and his colleagues initially thought dissolved organic carbon from long-dead marine animals and plants might be responsible for the green hue. However, a subsequent expedition in 1996 proved their initial theory wrong. Blue marine ice has the same amount of organic matter as green marine ice.
It was not until a few years ago that they came up with a new theory. An oceanographer from the University of Tasmania discovered that the marine ice at the bottom of the Amery Ice Shelf has 500 times more iron than the glacier ice at the top.
Iron Oxide In The Ice
Warren proposed that it was the iron oxide, which is typically found in soil and rocks, that is turning marine ice green. He explained that the minerals might have come from Antarctica's mainland when glaciers that flow over bedrock turned rocks into a fine powder and unloaded them into the ocean. When the rock dust got trapped under the ice shelf, it mixed with ocean water and became marine ice.
The theory suggests that green ice is more important than originally thought. Iron is a key nutrient that sustains all of marine life.
"It's like taking a package to the post office," stated Warren. "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."
The theory might also explain why iron is scarce in some areas of the ocean. The team is hoping to test their new theory. They hope to acquire samples from multiple icebergs with different colors to analyze their iron content and light-reflecting properties.