The question had been gnawing at him for over thirty years. But glaciologist Stephen Warren may have finally solved themystery of one icy enigma: that of the strange green colour sported by some icebergs in Antarctica.
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The glaciologist form the University of Washington first came across one of these weird and mysterious masses of greenish ice back in 1988. So he went on an expedition to the edge of the Amery Barrier, a heap of ice covering a large part of Prydz Bay, east of the southern continent, and he observed the enigmatic phenomenon for the first time in his career.
First meetings are very important
'When we climbed theiceberg, the most extraordinary thing was not the colour but rather the clarity. The ice did not have any bubbles, it was obvious that it was not ordinary ice from a glacier,' recalls the glaciologist. It was the first disturbing element that piqued the researcher's interest in these mysterious 'green icebergs'.
By analyzing this bubble-free ice, Stephen Warren and his colleagues discovered that it was indeed unusual ice: sea ice. Ice that does not form from the accumulation of snow but from the water of the ocean; and therefore does not trap air bubbles, as is the case in the rest of the glaciers.
This marine origin of the ice making up the green icebergs immediately made the researcher and his colleagues look towards a possible hypothesis: that of the presence of impurities coming from seawater, and responsible for the colour of the ice. The first step towards an explanation, but the precise nature of this impurity remained unknown.
The first option imagined by scientists: the presence of microscopic particles in the ice from the decomposition of plants or marine animals. Composed of organic carbon, these Microparticles have a yellowish tint. A hue that, in addition to the natural bluish tint of ice, could have given green icebergs their weird colour.
A hypothesis that fell into the water
In 1996 however, Stephen Warren and his colleagues hit the cold showers. Not that they fell into the icy waters of the Antarctic Ocean; but rather they discovered that the organic matter content of the green ice was absolutely the same as that of the blue icebergs. The hypothesis of organic Microparticles literally fell into the water.
It was only years later that the team was able to take a crucial step in solving the mystery thanks to the work of an oceanographer from the University of Tasmania. The scientist discovered, in ice cores taken from the famous Barrière d'Amery - the site of the first meeting between Stephen Warren and the green icebergs - a concentration of iron 500 times greater at the lower end of the core than at the top. A difference in size, which could explain the greenish tint of the sea ice composing the icebergs that preoccupied the researcher.
The origins of these iron oxides were yet to be determined. Particles that can give the ice hues from yellow to brown, through red and orange. And which in addition to the natural blue of the ice, would cause them to seem greenish in colour.
Particles straight from the continent
The hypothesis now advanced by Stephen Warren is that of an early origin. The slow-moving ice on the Antarctic Continent acts rather like a 'plane' on the rocky ground, producing a fine mineral powder, 'rock flour' if you will, rich in iron oxides. When the dust finally reaches the oceans, it mixes in the water and gets trapped in the ice formed in the famous icy sea. This process could finally shed light on the mystery of the green icebergs.
Beyond their thrilling aspect, these frozen masses could play a crucial role in the balance of the Antarctic ecosystem, Stephen Warren describes:
These icebergs could distribute this iron very far into the ocean, and then melt, making it available for phytoplankton that can use it as a form of nutrition.
It serves as food for flora at the very base of the entire marine food chain. The glaciologist concluded:
It has always been believed that green icebergs are just an exotic curiosity, but we now think that they might actually be important.
Thirty years the question poked at him; and now the answer about the origins of green icebergs is clear, probably going well beyond his expectations.
Check out the video above for more on this phenomenon...
