This is a very odd phenomenon
that is also unexpected. One understands
that mixing occurs, but not this gathering into a streamlet that descends to
the ocean floor and then explodes outward.
It is certainly a neat phenomenon and it is worthwhile to go to the BBC link and view their U-tube video.
This is also a reminder of the
inherent complexity of the sea ice/brine interface and that it has been
proposed as an incubator of life on snow ball earth. It may be active in slow motion but active it
is.
Unlike ordinary solids such as consolidating
ash, sand and rock, ice fractures easily and reglues continuously to shift stresses. The others do that also, but much
slower. Thus fluid fractionization is even
plausible and possible. This suggests a
whole range of unexpected slow motion chemistries may be possible here that
particularly preserve organics.
'Brinicle' ice finger of death filmed in Antarctic
By Ella DaviesReporter, BBC Nature
As brine from the sea ice sinks, a 'brinicle' forms threatening life on
the sea floor with a frosty fate.
23 November 2011 Last updated at 10:01
A bizarre underwater "icicle of death" has been filmed by a
BBC crew.
With time lapse cameras, specialists recorded salt water being excluded
from the sea ice and sinking.
The temperature of this sinking brine, which was well below 0C, caused
the water to freeze in an icy sheath around it.
Where the so-called "brinicle" met the sea bed, a web of ice
formed that froze everything it touched, including sea urchins and starfish.
The unusual phenomenon was filmed for the first time by cameramen Hugh
Miller and Doug Anderson for the BBC One series Frozen Planet.
Creeping ice
HOW DOES A BRINICLE FORM?
Dr Mark BrandonPolar 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."
Against the odds
Hugh had little room to position himself and the cameras under the ice
The location - beneath the ice off the foothills of the volcano Mount Erebus , in water as cold as -2C - was not easy to
access.
"That particular patch was difficult to get to. It was a long way
from the hole and it was quite narrow at times between the sea bed and the
ice," explained Mr Miller.
"I do remember it being a struggle... All the kit is very heavy
because it has to sit on the sea bed and not move for long periods of
time."
As well as the practicalities of setting up the equipment, the
filmmakers had to contend with interference from the local wildlife.
The large weddell seals in the area had no problems barging past and
breaking off brinicles as well as the filming equipment.
"The first time I did a timelapse at the spot a seal knocked it
over," said Mr Miller.
But the team's efforts were eventually rewarded with the first ever
footage of a brinicle forming.
No comments:
Post a Comment