Jade iceberg mystery

Researchers may have solved the century-old mystery of why some Antarctic icebergs are green.

Experiments on ice samples collected from the Amery Ice Shelf suggest that iron oxides in seawater are the likely explanation.

The research, led by Professor Steve Warren from the University of Washington, and involving Australian Antarctic Division Glaciologist Dr Mark Curran, was published in JGR Oceans in January.

“The remarkable jade colour is likely the result of yellow-tinted iron oxide in seawater, combining with the crystalline blue of the ice — much like mixing yellow and blue pigments together,” Dr Curran said.

The most commonly sighted Antarctic icebergs are made from blue-white glacial ice, which forms when snow falls on the Antarctic plateau and becomes compacted over thousands of years.

Jade icebergs are formed beneath the ocean, when mineral-rich seawater freezes to the underside of an ice shelf in layers, then eventually breaks off. These jade bergs contain layers of the blue-white glacial ice, and greener frozen seawater below. Green-striped icebergs form when seawater freezes into basal crevasses in glacial ice.

The scientists also believe that these mineral-rich ice blocks could play a role in promoting biological activity in the Southern Ocean, by transporting nutrient-rich water to areas where iron is in short supply.

David Reilly
Australian Antarctic Division