Antarctic Ice

Ice sheets first appeared on Antarctica about 30 million years ago. Ice sheets continually flow from the Antarctic interior outwardly like a gently flowing river toward the ocean. As the glacial ice sheets reach the coast they tend to break off due to gravity, waves, current, and tides. Along the coast a portion of the glacier begins to crack, slowly, like time stood still and finally with a loud thunder a portion of the ice sheet (“calve”) falls into the seas.

During the winter months sea ice is formed from the freezing ocean water surrounding Antarctica. The seas around Antarctica begin to freeze in March (autumn). The sea ice forms quickly reaching half of its maximum thickness within a month. During the Antarctic Spring and summer (October through January) the sea ice breaks apart. The sea ice is extremely important to the ecosystem. The green algae need it as a habitat. The krill eat the algae, and a lot of animals in the Antarctic eat the krill. During the Antarctic spring the algae’s green pigment absorbs the solar radiation warming up the ice faster and breaking up the ice much quicker than it had formed. Build up of sea ice over successive seasons leach the salt brine from the ice creating fresh drinkable ice.

Seawater does not freeze at 32 F (0 C). The salt content in the sea water lowers the freezing temperature of the saltwater to 28oF (-1.8 C). Ice that appears to have an oily-sheen is called “Grease ice”. The grease ice is created when the surface water begins to freeze and crystallize on the salty brine. Within an hour the once ice free water can turn into a slushy icy-water mixture known as “Frazil-ice”. As the Frazil-ice thickens the water below begins to freeze. When the sea water begins to thicken more than four-inches then the ice is in the Nilas stage of ice berg formation.

Ocean swells and wind break the sea ice into large pieces called pack ice. Wind and currents provide the ability for the pack ice to move. Pack ice can change direction as it packs up against other ice. These conditions can be very dangerous as pack ice can make the journey impassable in a matter of hours. In some areas around the Antarctic, sea ice never forms. These areas have been identified as good navigational routes. These large ice-free open areas surrounded by pack ice are called “Polynyas” and they can be more than 60 miles across.

During the Antarctic summer the icebergs melt and change in shape. The majority of the iceberg is below the water. During the shifting of weight, sometimes an iceberg will “Turtle” as pieces break off and the iceberg can turn partially or completely over.

Antarctica has much larger icebergs than the Arctic. A large iceberg may weigh more than 400 million tons, and be more than 100 feet (30 m) above the surface. Icebergs do eventually melt. Sometimes a large iceberg can melt for years or decades. Most icebergs are less than 400 feet (123 m) across the waterline. The large icebergs are tabular and break off the ice sheets. They are generally 650 feet (200 m) to 1000 feet (308 m) thick. Icebergs break up into pieces named “growler” (< 15 ft), “bergy bits” (15-46 ft), small (47-200 ft), medium 201-400 ft), large 401-670 ft) and very large > 670 ft), depending on their size. Ice berg age can be rounded, irregular, or tabular in form. In 2000, an ice sheet broke off the Ross Ice Shelf in the Antarctic creating a 6,875 mi2 (11,000 km2) iceberg called B-15. In 2002, B-15 broke and created B-15A an 1875 mi2 (3000 km2) iceberg that finally in 2005 broke up.

Currently, the sea ice around the Antarctic is becoming less. The algae is not able to find suitable habitat, the krill is unable to find enough algae, which is causing a shift in penguin colonies.