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Antarctica is located in what is commonly called the Southern Ocean,
one of the richest marine ecosystems in the world. Three basic water
masses comprise the Southern Ocean: Antarctic Surface Water, Circumpolar
Deep Water, and Antarctic Bottom Water.
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Changing
Sea Levels
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Three circumstances would result in sea
level changes:
Expansion of the volume of the world's
oceans as they warm up
Melting of valley glaciers
Changes in Antarctic and Greenlandic ice
sheets.
Existing data suggest that the average
world sea level has risen by 10 cm in the last century. During
that time, the Antarctic ice sheet is believed to have remained
roughly stable. It appears that sea level will continue rising
by 1 to 2mm per year, without any extra contribution from
the Antarctic. Even minor melting of the Antarctic ice cap
will significantly increase the rate of rise.
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The boundaries between the
water masses tend to be sharp. On the continental shelf of Antarctica,
there are two main water masses: Surface
Shelf Water and a modified version of Circumpolar Deep Water.
The seas south of the Antarctic Convergence
contain the coldest and densest water in the world.
This water, called Antarctic bottom water,
is formed as seawater sinks to the ocean floor when ice shelves
melt.
It then moves along the ocean floor into
the Northern Hemisphere, where it adds oxygen and reduces
the temperature of these seas to less than 2°C.
This cooling effect on trop ical and
temperate seas is an important feature of the world's heat
balance.
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Each water mass has different
characteristics, and these differences drive circulation around the
continent.
As part of the global heat
engine, the Antarctic has a major role in the world's transfer of
energy. Its ocean/atmosphere system is known to be both an indicator
and a component of climate change.
Oceanographers are
attempting to improve our understanding of this oceanic
environment, including global exchange of heat, salt, water, and trace
elements, sea-ice dynamics, and marine
biosphere research.
One of the most important
ocean processes-one that is uniquely related to the Antarctic-is
ocean ventilation, the process by which the deep ocean affects the
atmosphere on the time scale of decades to centuries. If we could
mark a cubic meter of sea water and follow its global meanderings
through the various oceanic current systems, we would find that
it spends most of its time isolated in the deep ocean, where it
is dark and cold.  Only
occasionally-once every 600 years on the average-would it appear
on the surface, and then only south of the Antarctic Circumpolar
Current. This process is called overturning or ventilation of the
ocean. Typically, when deep water reaches the surface, it gives
up heat to the much colder atmosphere and picks up dissolved atmospheric
gases, including carbon dioxide. The ventilation or overturning
of the ocean can significantly affect climate
change.
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The Antarctic
Convergence
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- The Antarctic Convergence, which encircles
Antarctica roughly 1,500 kilometers off the coast, divides
the cold southern water masses and warmer northern waters.
- An ocean current, the world's largest,
moves eastward around the continent at an average speed
of about half a knot, four times greater than the Gulf Stream.
- Sea ice up to 3 meters thick forms
outward from the continent every winter, making a belt 500
to 1,500 kilometers wide.
- Even in summer the sea ice belt is
150 to 800 kilometers in most places.
- The area of sea ice varies from 3 million
square kilometers in summer to 20 million square kilometers
in late winter.
- This water comprises 10% of the world's
oceans; as well as connecting the Atlantic, Pacific and
Indian oceans, it also isolates the continent from warmer
waters.
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