Sea Ice
Beyond the ice shelves is the sea and sea ice is the general term for any form of ice found at sea which has originated from the freezing of sea water (Sea ice includes grease ice, pancake ice, pack ice and frazil ice)
Each winter, the sea-ice around Antarctica grows to roughly twice the size of the continent. Although Antarctica sea-ice varies every year - it changes from approximately 3,000,000 square km in the spring to 20,000,000 square km in the winter - an area twice the size of Europe! This huge seasonal change has enormous repercussions, since the ice alters the exchange of heat, moisture and momentum between the sea and the air, and the marine ecosystem has to adapt to lower temperatures and a lack of light under the ice.
Antarctica's sea ice is very important for two major reasons:
Firstly, it has a direct affect on the marine ecosystem in Antarctica. When the sea ice melts each spring, there is a sudden blooming of microscopic plants (phytoplankton) which drift in the ocean currents. These plants thrive on the surface of the Southern Ocean as a result of the ice melting and make up the food for many small marine animals like krill and so the Antarctic food chain begins.
Antarctica's Sea Ice affects the weather patterns of the whole Southern Hemisphere as it acts like an insulating blanket over the Southern Ocean by stopping it from absorbing light and heat from the Sun. Sea Ice and the snow on top can filter out 99% of the light. As a result the presence of sea ice keeps the air cool and dry in Antarctica and then when the ice melts, it cools down the ocean and the atmosphere.
Most scientists agree that global warming is having a huge effect on the polar regions as the amount of ice covering the Southern Ocean has decreased. If the amount of sea ice decreases, the Southern Ocean can absorb more heat from the Sun. This makes the temperature still higher, so more ice starts to melt and so you have a circle of consequences.
Frazil Ice
Frazil ice is a collection of loose, randomly orientated needle-shaped ice crystals and is the first stage in the formation of sea ice. It resembles slush and has the appearance of being slightly oily when seen on the surface of water. It sporadically forms in open, turbulent, supercooled water, which means that it usually forms in rivers, lakes and oceans, on clear nights when the weather is colder, and air temperature reaches –6°C or lower.
Pancake Ice
Pancake ice are plates of ice that look like pancakes and have up-turned edges where the plates have bumped into each other.
Ice Floes
Ice-floes are flat pieces of floating ice and they can be any size from one or two metres across, to several metres.
Pack Ice
Pack Ice is formed when the sea has large ice-floes floating on it and it is the last stage of sea ice formation. As temperatures fall, the channels of water between the pack-ice close up as the ice-floes join together.
Pack Ice, open. Composed of floes seldom in contact and with many leads (a navigational passage through floating ice). Ice cover 4/10 to 6/10.
Pack Ice, close. Pack-ice which the concentration is 7/10 – 8/10, composed of floes mostly in contact.
Pack Ice, very close. Pack-ice in which the floes are tightly packed but not frozen together, with little sea ice visible. Ice cover practically 10/10.
Pack Ice, consolidated. Pack-ice in which the concentration is 10/10. The floes are frozen together with no water visible.
Many explorers have had their ship trapped in pack ice in Antarctica, and Ernest Shackleton's Ship, Endurance was crushed by pack ice in 1915.
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