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ArticlesWhat's
to see in the ocean?
What's to see in the Ocean?
Solar Powered
 The
ocean plays an essential role in the world's climate system,
absorbing about half the heat from the sun. The heat escapes
to warm the atmosphere, mainly through evaporation either
locally or months or years later having been transported by
ocean currents thousands of kilometres.
The
upper three metres of the ocean can hold more heat
than the entire atmosphere, and sea surface
and subsurface temperatures are now used by meteorologists
when they make climate forecasts.
The
sun's energy also drives large-scale wind systems and cells
in the atmosphere. In turn, the winds, along with sinking
cold water in the polar and subpolar oceans, drive the ocean.
The resulting ocean currents redistribute the energy absorbed
from the sun throughout the world's oceans, carrying it away
from the region of greatest heat in the tropics towards the
colder polar regions.
Australia's
climate variability is strongly influenced by the Pacific
Ocean, the El Niņo/Southern Oscillation phenomenon and sea
surface temperature patterns in the Indian and Southern Oceans.
Long term, the Southern Ocean is critical in evaluating the
timing and regional impacts of climate change.
Ocean Circulation
 Winds
move across the earth's surface towards the west near the
equator (trade winds) and towards the east in the temperate
mid-latitudes (Westerlies and Roaring Forties). Their effects
create large circulation patterns in each of the Atlantic,
Indian and Pacific Ocean basins, moving clockwise
north of the equator and anticlockwise south of the equator.
The
gyres (or circular motions) move water from equatorial to
polar regions along the eastern coasts of continents as intense
warm currents (like the East Australia Current). In regions
near the equator, water in the gyres also moves vertically,
bringing cooler water towards the surface. When warmer water
moves south towards the Antarctic, it releases its heat into
the atmosphere.
In
the deep ocean (at depths below about one
kilometre), water movement is governed by variations in the
density of water. In the Arctic and Antarctic regions, surface
waters become very dense as they cool. In addition, this density
is increased as sea-ice forms, releasing salts to the water.
Cold saline (dense) water sinks to the bottom of the ocean,
then circulates along the ocean floor, slowly mixing
upwards over decades or even centuries.
Along
the coastlines, local effects such as tides and coastal winds,
sediments, nutrients and rainfall run-off combine to influence
the behaviour of continental seas.
Physical components of an ocean
 The
ocean has other physical components and external influences
governing its behaviour.
Waves
are generated by wind and may travel thousands of kilometres
across the oceans. Engineers must have a knowledge of the
potential force of waves in extreme conditions when they design
coastal shipping facilities and oil drilling platforms.
Ocean
currents transport water in varying volumes. The Antarctic
Circumpolar Current, the world's largest ocean current, can
move around 150 times the volume of Sydney Harbour per second
(500,000 megalitres) and even the much smaller Leeuwin Current
transports five to ten 'Sydney Harbours' per second down the
coastline of Western Australia. The strength, direction and
volume of water carried by ocean currents can vary from season
to season and from year to year, influenced in complex ways
by factors such as El Niņo.
In
cross-section, the ocean is like an onion with many different
water layers. The surface layer may be tens of metres thick.
Beneath it are other layers that originate from thousands
of kilometres away. For example, two of the deep layers
off the Australian east coast originate in the Northern Hemisphere
and in the Antarctic. Oceanographers infer the origins of
these waters from their temperature and salinity, which together
are effectively their signatures.
Ocean
eddies are formed on the edge of strong ocean currents; they
are typically 100-200 kilometres in diameter and circulate
both clockwise and anti-clockwise. They are detected by satellite
as roughly circular patches of high or low water and may contain
currents of up to four knots, be as deep as one kilometre
and circulate for several years before losing momentum. These
eddies are similar to the high and low pressure systems in
the weather charts. Oceanographers can track the speed and
direction of ocean eddies by studying photographs taken by
satellite.
Scientific
interpretation of how ocean eddies form and their
effects is important in mapping ocean circulation. Such information
is sought by authorities such as the Australian Maritime Safety
Authority for search and rescue at sea and also for environmental
protection.
Upwelling
is another phenomenon of oceans. It occurs when strong winds
bring dense waters to the surface, against the force of gravity.
Upwelling is important to the ocean ecosystems because it
solves the dilemma of life in the ocean. For example, how
does the food-chain begin when sunlight is only available
near the surface, but essential nutrients from decaying organic
matter are on the ocean floor? The answer is that upwelling
returns nutrients to the surface. The richer fishing grounds
of the world depend on a flourishing food chain, and it is
interesting to note that Australia does not have any really
rich fishing grounds because the winds here are generally
not conducive to upwelling.
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