This is actually a mail which i had received today. I think it reveals some interesting facts:-)
The air in Antarctica is frequently very dry. The low temperatures mean that little or no water vapour is held in the air, instead it freezes and falls out, or builds up on surfaces as frost. Sometimes however depending on the particular atmospheric conditions, the frozen water vapour remains in the air as suspended ice crystals. In these conditions the crystals can reflect sunlight in a variety of ways forming atmospheric phenomena of different types.
One of these phenomena is the "Solar Pillar" seen above. The sun is reflected very strongly so that the reflection is almost as bright as the sun itself. Like a rainbow, this sight is dependent on where the light is coming from and where the observer is standing. The pillar appears to move when the observer moves, but always remains directly below the sun.
At the beginning of the austral winter starting around March, the loose pack ice that has spent the summer months circling Antarctica begins to drift northwards. Pack ice is old sea-ice, frozen sea water that is a year old or more, it froze and formed elsewhere and later floated off with the winds and currents. Pack ice is heavy stuff and when it arrives somewhere it has the effect of steadying the ocean swell. The continuous rolling motion of the sea is stopped completely by a relatively narrow band of pack ice only 100m or so wide. The result is that where pack ice is present in reasonable quantity, the sea calms down sufficiently for low temperatures to freeze it easily - moving water cannot freeze as easily as static water.
This is sea-ice in the very early stages of formation. Sea-ice that forms in situ and is attached to the coast is called "fast-ice", it is stuck fast. In this picture the surface of the sea is beginning to freeze as the temperature is dropping to -20C and below. Pack ice has come near to the shore and so all movement of the sea has been killed completely allowing low temperatures to freeze the sea water. At this stage the ice is around an inch (2.5cm) thick but it has a spongy texture, you could poke a finger or certainly a fist through it relatively easily. The patterned effect comes from the rise and fall of the tides. As the tide rises, so the surface of the sea enlarges slightly and so the ice cracks apart, as the tide falls, so the surface of the sea decreases slightly and so the slabs of ice overlap at the edges.
Sea ice in the process of forming, the shore of the island in the distance is about 5 miles (8 kilometers) away and the whole of the sea surface in-between is made of forming fast ice. Notice how the slabs of forming ice become larger further out to sea as there are less undulations of the coast to push the slabs together as the tide falls
The ice near to the shore here is known as "pancake-ice" . This is formed when slabs of ice that are forming are jostled by the wind and / or movement of the sea. The pancakes of ice bash against each other around the edges and start to curl upwards at the edges.
A picture taken of consolidated pack-ice. The ice that you see is mainly pack-ice, last years ice that formed elsewhere, broke up and floated here. As the temperature dropped, then this ice became stuck together by fast-ice, sea-water frozen in situ and attached to the coast that acts as a glue for the loose bits of pack. The ice-bergs that you see have been frozen in position and will remain son until they are freed by the spring break-up of the surrounding sea-ice.
Once fast ice (sea-ice frozen in situ and attached to the coast) has become established, the patterns of the earlier pieces disappears. The tide still rises and falls however meaning that the sea surface expands and shrinks slightly as it does so. Tide cracks are a result of this movement (as ice is not known for its elastic properties) they are formed when the ice moves apart, they close again when the tide falls. A tide crack is often many miles long, in this case stretching for around 5 miles (8 kilometers), but never more than about 18", 45cm wide between Signy and Coronation Islands in the South Orkneys group. Tide cracks are valuable resources for wild-life as they provide a region where birds such as snow petrels can fish through for krill and also as a breathing hole for crab eater and Weddell seals.
This is pack-ice in the summer months around the Antarctic peninsula. The ice looks fairly continuous, but has quite a lot of open water between the pieces and so can be relatively easily pushed aside by an ice-strengthened ship, in this case HMS Endurance. Larger pieces such as this one that are hit by the bow of the ship crack up into smaller pieces.
Proper Ice breakers have rounded hulls and rounded bows rather than being sharp and pointed. When breaking through very thick ice, the front of the ship rides up over the ice and the weight of the ship breaks through.
Passage is slow though, and heavy on fuel. Most of all, it takes an experienced and well informed ice-pilot to be confident in entering such ice so as not to be locked into the pack should the wind direction change and consolidate the ice.
At the end of the winter, rising oceanic swells and increasing temperatures cause the stable winter sea-ice to break-up and begin to drift away from where it formed. This years fast-ice therefore becomes next years pack-ice with a portion of it melting and disappearing completely. Here a small inflatable zodiac-like craft is (not entirely sensibly) negotiating quite close, but relatively light pack-ice. One person drives the boat, while another sits on the bow pushing the larger pieces of ice out of the way with his feet.
If the wind gets up and closes the ice, it could well be goodbye to the boat and the people in it too.
Ice-bergs drift around the Southern Ocean carried by the currents and blown by the winds. In the winter the sea-ice freezes around them and effectively glues them in place until the spring when the ice breaks up and they can begin to move again.
During this frozen-in time, it is possible to travel out across the sea-ice and walk right up to the bergs. This guy in the picture has an almost identical picture to this - with me in front of the berg though.
It can be quite magical standing next to an ice-berg, especially when the sun is shining and glistening off the ice. The sun can also penetrate the ice and be reflected off inner surfaces giving a whole variety of effects and colours from white through a range of vivid blues, quite an unreal experience.
The tip of the "ice-berg." Everybody knows that most of an iceberg lies under the water, but most don't know that the amount beneath the surface varies from about 50% to 99%. The cause of the variation is largely in the amount of air that is trapped in the ice so affecting its buoyancy. An average iceberg will be about 80-90% beneath the surface. Very low lying pieces of ice of whatever size in the water are known as "growlers". These often have a green tinge to them.
They are known as growlers because they present a particular hazard to shipping with the small amount visible above the water and the colour making them especially difficult to see and therefore especially dangerous.
This is a part of a land-based snow slope. In the spring when the winters snow begins to melt, water flows across the top of glaciers and snow slopes carrying with it dissolved nutrients in the melt water. In these conditions, algae grows within the top layer of the ice or snow catching the goodies as they flow by and taking advantage of the extra energy from the longer days and stronger sunshine.
In this case the algae is predominantly a red-coloured species, but further down the slope, green and blue-green colours are discernable. This is relatively short-lived spring phenomena as soon the very snow and ice layer that the algae are living in will melt and the algae will flow down to the sea with the water that provides them with their nourishment. It is not unusual to see distinctly red, green or blue-green topped ice bergs in the spring as a result of the growth of such algae.
There are over 300 species of such algae that live in such harsh and cold conditions. The red colour is a protective chemical (carotenoids such as astaxanthin) that the alga produces against exceptionally high concentrations of visible and ultra violet light that bounces off the snow and ice surfaces and so saturates them to a point where it become harmful and destructive. Such algae are also found in other parts of the world, often in high mountains where extra u-v light due to the thinner atmosphere and again increased light scattering by ice and snow requires protection by similar pigments.
Sometimes, walking across such an area will leave behind red footprints as the algae are concentrated by the walker as the snow is crushed, and sometimes there will be a a faint smell of fresh watermelon accompanying the phenomena.
Ice bergs are carved and shaped by wind and wave. As they are eroded, so the balance changes and they tip up to a new stable position. This continuous erosion, moving around and occasional breaking up into smaller pieces produces all kinds of weird and wonderful shapes that belies their original origin as a part of a flat freshwater glacier.
Ice bergs are eroded by a combination of temperatures above freezing and the effects of wave action. Here in a fairly rough sea, waves are washing up the side of this berg to a point about 2 metres above sea level and will probably make two separate upright areas that are divided by the developing trough. We did for a short time consider trying to speed through the gap when it was awash in our small powerfully driven zodiac boat, but decided against it - probably for the best!
The hard angular shapes and edges of this berg remind me of a cubist painting. Notice that the area at sea-level towards the left is very smooth and curved by contrast to the rest of the ice. The sharp geometric edges will probably have been made when this piece of ice calved from its glacier, the fracture planes of the ice being usually straight and plate-like. That it is not yet smoothed out indicates that this region has not yet been under the water to be sculptured into the more usual curves seen on ice bergs, it also means that it only recently fell off the glacier, although it could well be a fracture plane from the collapse of a larger ice berg that broke into pieces.
It's windy in Antarctica, like nowhere else on earth, so the clouds go scurrying by most days giving ample opportunity for photography. If the lighting isn't quite right at the moment, then just wait a little while and it soon will be - but not for long.
I used to think that a new word was required to describe the scenery in Antarctica, around the coast it was frequently difficult to tell where the land ended and the sea began, and sometimes what was land, glacier, sea-ice or ice berg all blended into a single continuous flow of features. "Whitescape" sums it up for me although that belies the subtlety of the details of the vistas. Everywhere consists of white and shades of blue, as made by an artist with a limited palette, and with so much reflection around, there are no real dark shadows.
Clear skies mean clear sunsets, but because of the high latitudes, they develop and fade quickly. Snow and ice are a great bonus in sunsets as they colour up beautifully in reflection, in these conditions, beautiful sunsets don't even need to contain the sun in the picture.
This picture captures a very rare calm moment where there was no breeze at all to cause ripples on the sea and so disrupt the reflection. There was just enough time for me to get into position, grab a few shots and then sure enough, back came the wind and away went the reflection.
Mountains in the Antarctic interior are few and far between. Many are a special kind of mountain called a "nunatak". The Trans Antarctic Mountains that stretch from one side of the continent to the other break through the ice cap in places to form such nunataks - they are mountains that are surrounded completely by an ice field. A sort of cold version of the ocean and islands except that these are on land and raised high above sea level.
Due to their isolation and sterile surroundings, many nunataks are little or never visited, though there are records of some Antarctic birds such as snow petrels nesting on nunataks over a hundred kilometres from the coast where they feed. Why they do so is unknown, maybe they just like the scenery.
2 comments:
Sucha long post..I jsut scrolled by with the second half...
janani(){
:-) Thxs for spending that much time friend...
}
Post a Comment