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Australia: The Land Where Time Began |
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Tethys Ocean Stirring
According to the author3 the currents of the ocean are more
than 2000 times more powerful than any river on land. The currents of
the ocean never stop, continuously moving vast volumes of water around
the globe. The currents of the world's oceans are powered by the winds,
that are in turn powered by the Sun, so the energy supply is effectively
limitless, the constant movement of air being transmitted to the ocean
over which it blows. The distribution of the landmasses on the surface
of the Earth affects the flow of currents around the world, so the
currents have changed a number of times as the continents have been
shunted around. The Gulf Stream in the western North Atlantic is said
transport more than 55 million m3 of water per second, about
1000 times the total discharge from the top 20 rivers combined. The
Canary Current is a broader return flow in a southerly direction that
travels slower along the eastern margin of the basin. Resulting from the
north-south orientation of continents and of the oceans between them, in
each ocean, to the north and south of the equator, there are similar
gyres.
The
Southern Ocean,
that encircles Antarctica, is the only ocean in which there currents
encounter no impediments to their flow. The flow of the currents in the
Southern Ocean very effectively insulates the polar region from the
equatorial waters.
Abyssal currents that flow along the floor of the oceans, that are
linked to the surface currents, are powerful and slow-moving. These deep
currents are powered by density differences caused by variations in
water temperature and salinity. As sea water freezes at the poles it
excludes 70 % of the salt as it becomes ice, forming salt-enriched water
that is denser so sinks to the sea floor to become part of the global
thermohaline circulation system as it flows towards the equator. The
surface and bottom currents collectively form vast oceanic network of
currents that circulates and transfers heat energy, as well as other
nutrients, and sediment around the world. Wally Broecker called it the
'global conveyor belt'. The high temperature differential between the
poles and the equator is the main driver of this ocean conveyor current,
coupled with seasonal sea ice development. It has been estimated that
any particular water molecule would take 1000-1500 years to travel 1
complete cycle.
It has been found that the oceans are a crucial factor in the workings
of the climate systems of the Earth, storing heat, and obviously
moisture, in immense quantities, serving to moderate change and then
prolonging the new conditions once changes have occurred. As the oceans
hold more the 50 times as much CO2 as the atmosphere, the
cold high-latitude waters hold more dissolved oxygen than the warmer
waters of the lower latitudes. The ocean surface acts like a 2-way
control valve for gas exchange between the oceans and the atmosphere
that opens in response to the 2 main factors of gas concentration and
the stirring of the oceans.
Given the ocean circulation resulting from the present distribution of
continents, the author3 suggests the present is a temporary
warm spell in an icehouse world, in which the average surface
temperature of the sea surface ranges from 27o C at the
equator to -1.5o C near Antarctica. The water deeper than
2000 m are uniformly cold at 1-4o C. Landmasses in the polar
region are covered by ice that is thick and permanent, and the extensive
sea-ice forms annually. Trends towards global warming are beginning to
temper these extremes, though the global temperature are not yet near
the greenhouse world of the Cretaceous.
Another important aspect of ocean circulation is the upwelling that
occurs in the oceans and the stirring of nutrients essential for primary
production. Carbon, nitrogen, phosphorus and silicon, as well as trace
elements such as iron that is used for chlorophyll and other pigments,
that are brought abundantly to the oceans from rivers that carry
billions of tons of chemical and organic detritus to the oceans. The
same elements are present in the cells of animals, being released back
to the oceans by the decaying of dead animals as bacteria recycle dead
and decaying organisms, as well as their faeces. There is a tendency for
these organic materials to rapidly fall to the seafloor taking the vital
nutrients with them. In upwelling regions they are brought to the
surface most effectively, where cooler waters from a depth of several
hundred metres are brought to the surface, as well as by thorough mixing
of the upper ocean layer during major storms.
Where different masses of water meet in the oceans and deeper water is
allowed to reach the surface by circulation upwelling occurs. This
occurs in 1 prominent belt in the equatorial region and 2 high latitude
belts. In some coastal areas where the prevailing surface currents flow
away from the land dragging the deeper waters
to the surface it is even more pronounced. This type of upwelling occurs
off the west coast of West Africa, Chile-Peru and California. Stow, Dorrik, 2010, Vanished Ocean; How Tethys Reshaped the World, Oxford University Press.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |