Time Lapse: “Icicle of death”

Şi dacă e duminică, e Time Lapse!

Time Lapse este o tehnică a cinematografiei, care presupune fotografierea repetată la intervale prestabilite a unui obiect, peisaj, construcţie, fenomen al naturii etc. şi redarea fotografiilor la o viteză mult mai mare decat viteza la care au fost imortalizate pentru a crea un efect care să sugereze o accelerare a evenimentelor.

De exemplu, o scenă fotografiată o dată la fiecare secundă, şi apoi redată cu un frame rate de 30fps (frames per second), o să inducă o creştere in vietza acţiunii de 30 de ori.

Clipul de mai jos, a fost filmat de o echipă BBC în cadrul emisiunii “BBC One series Frozen Planet”, folosind tehnologia Time Lapse. DiferenÅ£a de temperatură în timpul iernii dintre aerul de deasupra oceanului ÅŸi apa oceanului este foarte mare, iar un astfel de filon de gheaţă poate să prindă contur, dar o explicaÅ£ie detaliată, venind de la Dr Mark Brandon, Polar oceanographer, @ The Open University puteÅ£i găsi sub clip.

Dr Mark Brandon Polar oceanographer, The Open University

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.

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.

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.

The icy phenomenon is caused by cold, sinking brine, which is more dense than the rest of the sea water. It forms a brinicle as it contacts warmer water below the surface.

Mr Miller set up the rig of timelapse equipment to capture the growing brinicle under the ice at Little Razorback Island, near Antarctica’s Ross Archipelago.

“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.”