Icebergs are formed when large blocks of ice breaks off from glaciers ice shelf and is floating in open water. Because glaciers are built up from snow falling on the Antarctic continent over millennia, this ice consists of pure fresh water. This floating chunk of freshwater ice then interacts with seawater beneath them it.
As seawater is drawn deep under the ice shelves by the oceanic currents, it becomes supercooled and freezes to the base of the ice shelf. Because this ice is formed from seawater that contains organic matter and minerals it causes variety of colour and texture to the iceberg. As the bergs become fragmented and sculpted by the wind and waves, the different coloured layers can develop striking patterns.
Striped icebergs in a variety of colours, including brown, black, yellow, and blue has been spotted in freezing waters around Antarctica. These following images were photographed by Norwegian sailor Oyvind Tangen, on board a research ship around 1,700miles south of Cape Town and 660miles north of the Antarctic in 2008. Photo credit.
Normally an iceberg appears white as a result of the tiny bubbles trapped within which scatter light in every direction. Blue stripes are created when a crevice in the ice sheet fills up with meltwater and freezes so quickly that no bubbles form. Ice that is bubble free has a blue tint which is due to the same light phenomenon that tints the sky - the wavelength of blue light causes it to be scattered or spread around much more than the other colours. When an iceberg falls into the sea, a layer of salty seawater can freeze to the underside. If this is rich in algae, it can form a green stripe. Other hues such as brown, black and yellow are caused by sediment, picked up when the ice sheet grinds downhill towards the sea.
Another picture of a striped iceberg. Photo credit.
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