Research: Mystery of green icebergs may soon be solved

James Marshall
March 8, 2019

The problem nagged at Professor Warren until 2016, when another research team tested an ice core from the Amery Ice Shelf for its iron content.

This frozen seawater is also known as marine ice, and it can contain organic and inorganic particles that can add some shades of green to the ice that usually comes in shades of white and blue as you know. However, the bottom layer of the iceberg, which is submerged in water, is made out of marine ice, which doesn't have any air pockets to reflect light.

The marine‐ice portions of icebergs are clear, dark, and green in colour more often than not. If experiments show the brand new concept proper, it could imply inexperienced icebergs are ferrying treasured iron from Antarctica's mainland to the open sea once they break off, offering this key nutrient to the organisms that assist practically all marine life.

He wondered if it was possible iron oxides are turning the common blue hue of ice a dark green.

For decades, scientists have argued about the cause behind the weird phenomenon and debated why the green-hued ice chunks aren't the typical blue or white color.

Glacier ice, originating from snowfall, flows off the Antarctic Ice Sheet to float on the ocean as ice shelves.

Now Stephen Warren, a glaciologist at the University of Washington, and his colleagues may have finally solved the mystery. "But iron is scarce in many areas of the ocean", they explained. They appear bluish-white, intermediate between the blue of pure ice, and the white of snow, because glacier ice contains numerous bubbles that scatter light. They suspected an impurity in the ocean water underneath the Amery Ice Shelf was turning some marine ice green. But a sample of the ice proved their theory wrong: green and blue marine ice have similar amounts of organic material.

Figure showing marine ice
Seawater sometimes freezes to the underside of ice shelves creating a layer of what’s called marine ice. Credit AGU

"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 colour of green icebergs is caused more by iron‐oxide minerals than by dissolved organic carbon".

The bottom of the core of green ice had almost 500 times more iron than the glacial ice above. They claim that iron oxide, a mineral found in soil and rocks, is responsible for the unusual emerald green tint.

The Daily Mail writes that Scientists discovered large amounts of iron in the polar ice and theorized that "foreign constituents" in seawater, particularly iron-oxide, can change its color. But where was the iron coming from?

A partly capsized iceberg embedded in sea ice. When the rock dust got trapped under the ice shelf, it mixed with ocean water and became marine ice. Warren believes the answer may lie in "glacial flour" - the powder formed from glaciers grinding over bedrock, eroding particles from the surface.

The researchers are now proposing to study icebergs of different colors for their iron content and light-reflecting properties. "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", Warren said in a statement.

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

Other reports by Click Lancashire

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