Icebergs can be surprisingly colorful

Imagine an iceberg and you will do probably imagine something white like snow coming out of a blue sea. But icebergs – and their tiny counterparts, known as adorable bergy bits and Burgundians – can take all sorts of nuances, from icy blue to striped to a seductive green.

Researchers and sailors have been observing emerald icebergs for years – a piece of ice "up to the mast" and "green as emerald" figured even in Samuel Taylor Coleridge's 1834 poem, "Rhyme of the old sailor ". exactly why these icebergs look the same. In a new article in the journal American Geophysical Union JGR Oceans, researchers led by Stephen Warren, glaciologist and professor emeritus at the University of Washington, offer a new theory on exactly how these floating monsters get their greenish hues.

All of this has to do with the making of icebergs. Icebergs stand out from glaciers or ice trays, mainly around Antarctica and Greenland. Since they begin life in the form of snowfall that accumulates over time, icebergs contain pockets of air in the form of bubbles that disperse the light. With a few exceptions and with occasional scratches, glacier ice tends to be a bluish white.

When the icebergs are in the ocean, their composition changes when the seawater, as well as the minerals and organic particles it contains, freezes at the base. This is called "sea ice" and is sometimes exposed if an iceberg spills. This newly formed material is often amazing – it sometimes looks marbled, pierced with blue or green vitreous streaks.

In the 1980s, Warren had discovered green icebergs since his visit to the Mawson Research Station near the Amery Antarctic ice shelf in the 1980s. His first impression was that green was a produced dissolved carbon from decaying plants or marine animals, but the samples did not prove it. Another idea began to take shape after researchers at the University of Tasmania published an article in 2016 reporting that they had found a high concentration of iron in a sea ice sample from the core of Tasmania. Amery ice cream. This brought Warren to think. "When I read their diary, I realized that it could explain the green color of icebergs," he says.

When glaciers scrape land, they produce what is known as glacier flour – a product of rock in place crushed by the moving mass. When glaciers retreat, these geological debris is usually carried away in water, sometimes too small particles to be visible to the naked eye. But on earth, soils and rocks contain iron oxides often tinged with red, such as reds, yellows and browns. Since the Tasmanian team discovered that sea ice contained 500 times more iron than glacier ice, Warren asked if sediments were causing the green color of icebergs. The ice absorbs the red light, while the iron oxides absorb the blue light. The assumption is that when iron oxides appear in the sea ice, "the color will turn green," explains Warren.

He does not know for sure. He hopes to get funding so that he and his colleagues in Tasmania can return to the area around the Amery pack ice and study the icebergs themselves. If he has the opportunity, Warren plans to examine the 'berg' blue, green, blue, green and yellowish green ', to measure the spectrum of light reflected to each and to sample new ones. samples. For the moment, green icebergs remain a magnificent mystery.