Since long before the 1900’s, explorers and sailors around Antarctica have been greeted by the sight of beautiful, but strange, green icebergs. Researchers have been perplexed for decades by the unusually colored ice formations.
The mystery may finally be laid to rest, however. A recent publication released in the Journal of Geophysical Research: Oceans reports that the brilliant emerald green colorations occur because of mainland Antarctica’s rock dust is heavy in iron oxides. The findings were revealed by a University of Washington glaciologist team, headed by Stephen Warren.
In a Newsweek report, Warren explained that the green icebergs wouldn’t have been seen before 1774’s discovery of the Antarctic Ocean by James Cook’s expedition. In fact, a famous poem, The Rime of the Ancient Mariner by Coleridge, describes the phenomenon:
“Ice, mast high, came floating by, as green as emerald.” It seems this was based on fact, not poetic license.
Warren went on to explain that a German expedition in 1903 noted the green icebergs, and they made the scientific headlines in 1921. The novelty has been spotted on occasion by a number of sea captains and explorers.
When ice breaks apart from an ice shelf or a glacier, it forms an iceberg. Layers and layers of snow will pile onto the iceberg, gradually becoming solid. These formations will contain light reflecting air pockets. The iceberg absorbs less blue light than red, giving them a bluish appearance.
Layers Of Different Ice
The emerald green icebergs in the Antarctic Ocean contain layers of frozen ocean water under the ice shelf. This marine ice lacks air pockets, making the icebergs look darker and more clear than normal icebergs. According to Warren, one percent of all icebergs have this layer of visible marine ice.
The theory behind the green icebergs was traditionally that they were formed out of marine ice, not glacier ice. The iceberg, it was thought, would take on a greenish hue because of dead marine animals or plants trapped in it as it froze. When this organic material began to break down, it took on a yellowish tinge as it produced organic carbons. The green color, accordingly, was as elementary as this yellow marine ice mixing with the blue tinged glacier ice.
Warren, however, found that the same amounts of organic materials were found in both blue ice and the green. This 1990’s discovery torpedoed the long-standing theory. Something else had to be at work within the green icebergs.
A recent discovery by Tasmanian researchers found that an ice sample taken from the Antarctica Amery Ice Shelf had a significantly higher iron content at its base than was produced by the glacier ice above. In fact, there was nearly 500 times more iron at the base of the core sample.
Rocks and soils that have heavy iron oxide content will be red, yellow or orange in color. Warren began to consider that perhaps this is why the icebergs in Antarctica were green. The researchers theorized that when ocean water mixes with the mainland rock of Antarctica, the result was green marine ice. If the ice turned over as it was breaking away from the main ice sheet, the green bottom layer would be exposed and create a green iceberg.
Scientists are considering the uses of this information and suggest that these icebergs play an important role as a delivery system of iron nutrients to the Southern Ocean. Tiny marine plants at the bottom of the food chain, known as phytoplankton, need iron to survive.
Warren believes that the green icebergs are responsible for delivering iron directly to the phytoplankton that use it. This means that green icebergs are more than just a bizarre fluke of nature, they are, in fact, very important to marine life.
Currently, Warren is teaming up with colleagues from the Hobart, Australia Antarctic Center for more testing. They are hoping to gather more iceberg samples of all colors to check iron content and prove the theory. The Australian team specialize in measuring the levels of iron in seawater and sea ice.
Warren says, “If our project is approved, we will travel by ship to the Australian Antarctic stations close to the Amery Ice Shelf, where green icebergs are commonly found. The iron analyses will be done in Australia. Spectral reflectance of icebergs will be measured by others of our group. We have submitted a proposal to do this work.”