Friday 25 November 2011



November 23, 2011 

Creeping ice

A very cool video of an “icicle of death” was filmed with time-lapse camera in the freezing waters of the deep. The unusual phenomenon was filmed for the first time by cameramen Hugh Miller and Doug Anderson for the BBC One series Frozen Planet and is one of the most amazing shots ever recorded.

In the video, we can appreciate as the icy finger forms. It grows slows but when it touches down on the ocean floor, as it entombs whatever life-form that happens to be in its path.

Starfish and sea-urchins shrivel up and die, encased in a “tomb of ice” as the frozen tornado whirls its destructive path to the sea floor.

Freezing sea water doesn’t make ice like the stuff you grow in your freezer. Instead of a solid dense lump, it is more like a seawater-soaked sponge with a tiny network of brine channels within it

The “icicle of death” is caused by cold, sinking brine, which is denser than the rest of the sea water. It forms a brinicle as it contacts warmer water below the surface.

Brinicles are found in both the Arctic and the Antarctic, but it has to be relatively calm for them to grow as long as the ones the Frozen Planet team observed.

They used to be called ice stalactites until 1974, until a new theory was advanced as to how they are created.

In winter, the air temperature above the sea ice can be below -20C, whereas the sea water is only about -1.9C. Heat flows from the warmer sea up to the very cold air, forming new ice from the bottom. The salt in this newly formed ice is concentrated and pushed into the brine channels. And because it is very cold and salty, it is denser than the water beneath.

The result is the brine sinks in a descending plume. But as this extremely cold brine leaves the sea ice, it freezes the relatively fresh seawater it comes in contact with. This forms a fragile tube of ice around the descending plume, which grows into what has been called a brinicle.

The extremely salty 'brinicle' is not quite a solid icicle. The sea water is only forming a frozen 'sheath' around the cold saline, rather than freezing all the way through. Dr Mark Brandon, a polar oceanographer, described it as "a seawater-soaked sponge with a tiny network of brine channels within it."

Mr. Miller set up the rig of time lapse equipment to capture the growing brinicle under the ice at Little Razorback Island, near Antarctica’s Ross Archipelago. Navigating the icy ocean floor amid sea proved difficult. Inquisitive seals pushed the camera about.

“When we were exploring around that island we came across an area where there had been three or four [brinicles] previously and there was one actually happening,” Mr Miller told BBC Nature.

The diving specialists noted the temperature and returned to the area as soon as the same conditions were repeated.

“It was a bit of a race against time because no-one really knew how fast they formed,” said Mr. Miller.

“The one we’d seen a week before was getting longer in front of our eyes… the whole thing only took five, six hours.”

Read the full article: BBC News

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