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Short Stories for Teachers

Amazing Icebergs and Their Role in the Ecosystem
By:Stephen L Bynum

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

Antarctica has much larger icebergs than the Arctic. The broken shelves are generally 650 feet (200 m) to 1000 feet (308 m) thick and when they collapse into the water icebergs are formed. The "bergs" size defines their name such as "growler" (< 15 feet), "bergy bits" (15-46 feet), small (47-200 feet), medium (201-400 feet), large (401-670 feet) and very large (> 670 feet). The "bergs" can be rounded, irregular, or tabular in form. In 2000, a glacier broke off the Ross Ice Shelf in the Antarctic creating a 6,875 sq. mi. (11,000 sq. km.) large, genuine, floating, water mountain called B-15. In 2002, B-15 broke and created B-15A an 1875 sq. mi. (3000 sq. km.) solid, fluid, mound that finally in 2005 broke up into smaller pieces.

During the winter months frozen saltwater surround the Antarctic. The seas around Antarctica begin to solidify in March, beginning of the southern hemisphere autumn. The sea petrifies quickly reaching half its expected annual maximum thickness within a month. The salinity content lowers the freezing temperature of the saltwater to 28 F (-1.8 C). An oily sheen ("grease-ice") is seen on the surface of the water as the first frosting of liquid appears. This oily sheen is created when the surface water begins to freeze and crystallize on the salty brine. Within an hour the once fluid water can turn into a slushy mixture known as "Frazil". As the "frazil" thickens the water below begins to congeal into a frozen statuesque "nilas" more than four-inches thick. Ocean swells and wind break the rock-hard liquid into large pieces called "Pack-ice". Wind and currents provide the ability for the "pack" to move. As these concrete moisture slabs move about they tend to play"bumper cars" with each other and with a jolt they are quickly heading in another direction. These conditions can be very dangerous as the "pack" can make the journey impassable in a matter of hours. Open navigable waterways "polynyas" can be found around Antarctica year round. Polynyas are large open water areas surrounded by "packs" and they can be more than 60 miles across. During the Antarctic spring and summer (October through January) the unmoving sea breaks apart. The icebergs melt and change in shape. These frozen, watery, sculptures will sometimes "turtle" as pieces break off to turn the large motionless cube partially or completely over.

The ice is extremely important to the ecosystem. The algae need it as a habitat. The krill eat the algae, and the many animals of the Antarctic eat the krill. During the Antarctic spring the green pigment from the algae absorb the solar radiation, warming up the motionless sea quicker than it had formed. Antarctic ice appears to be trending toward less amounts. The algae is not able to find suitable habitat, the krill is unable to find enough food, and the chain of life is shifting ... creating an ecosystem in flux.

Stephen L. Bynum, 636-527-6008
sbynum@scientificprinciple.net
Scientific Principle, Inc.
http://www.scientificprinciple.net

Mr. Bynum is dedicated to the sciences involving biology, environment, oceanographic, and geological applications. He has worked in oceanography, archaeology, paleobotany, and as an environmental regulator. Mr. Bynum has worked in the Antarctic, South Pacific, and across the United States.






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