The Mystery of Antarctica's Rare Emerald Icebergs

Several articles have been published about this strange phenomenon. Most recently, scientists have proposed a new idea about why the mysterious icebergs are emerald in color.

The search for the mystery of the green icebergs began during an expedition by Australian scientists in 1988.

“Normal icebergs come from snow, and as snow is compressed under its own weight into ice, the air in the snow is trapped like bubbles. So glaciers contain a lot of bubbles, and icebergs are very shiny. But these icebergs are not like that,” said researcher Warren.

However, there were no bubbles in the emerald ice, suggesting it was not ordinary glacial ice. Warren took a core sample from a glacier near the Amery Ice Shelf in East Antarctica and compared it to other green ice samples from Australian expeditions in the 1980s. He found that the emerald colour was clearly due to sea ice, not glacial ice.

Most icebergs seen by sailors in Antarctica are white or blue, some even have stripes. True green is very rare.

At first, Warren’s team suspected that impurities in the seawater below were turning the ice blue, perhaps from trapped microscopic particles of dead marine plants and animals. But a sample of the ice proved their theory wrong: The blue sea ice had similar amounts of organic matter.

It wasn’t until a few years ago that Warren was inspired to have another go. His inspiration came from research by University of Tasmania oceanographer Laura Herraiz-Borreguero, who found that the Amery Ice Core had nearly 500 times more iron than the ice above it.

Warren wondered if it was possible that iron oxides were turning the common blue color of ice a deep blue. If so, where did the iron come from? These compounds are rare in many parts of the ocean. Warren believes the answer may lie in glacial limestone powder. These iron-rich particles then flow into the ocean and become trapped under the ice shelf, where they mix with marine ice as it forms.

This discovery could play a role in sustaining life in the oceans. Iron is an important nutrient for many other organisms. If blue icebergs are transporting iron from the Antarctic continent to the Southern Ocean, it could be a crucial process for marine life.

“Iron is a limiting nutrient for phytoplankton in the Southern Ocean, so biological oceanographers are keen to quantify different sources of iron,” Warren wrote in the Journal of Geophysical Research.

Phytoplankton are the base of the food chain in the Southern Ocean. Photosynthesis by these phytoplankton also removes CO₂from the atmosphere, so they are important in the global carbon cycle. With global warming, if the seawater flowing under the ice shelves becomes warmer, then perhaps less sea ice will form and less iron will be transferred to the phytoplankton.

To confirm this hypothesis, the team recommends further analysis of short cores from the iceberg to measure dissolved organic carbon and particulate organic carbon relative to depth, as well as the mineralogy of the iron.