Natural systems
Oceanic circulations
To find out more about oceanic circulation, read through the table below.
1
Ocean currents: The oceans are constantly moving horizontally and
vertically. Currents circulate warm and cool waters around the globe
between the equatorial zone and the poles, and between shallow and
deep waters.
Oceanic movement is driven by two main factors. The first is winds.
These generally result in surface ocean currents. Horizontal ocean
currents moving north and south of the equator carry warm water
towards the cooler waters near the poles, while these cooler waters
circulate back towards the equatorial zone. The atmosphere above
these waters is influenced by their temperature, contributing to the
climatic characteristics of certain regions. For example, areas
associated with warm ocean currents tend to have higher rainfall due
to the warming of the atmosphere and increased moisture contained
within it.
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2
The second is variations in temperature and salt content. These result
in the large-scale ocean circulation known as thermohaline
circulation (or the great ocean conveyor). Salt levels also
influence the movement of water and therefore climate. Ocean waters
experiencing high evaporation and low precipitation have increased
salinity levels. The resulting increase in density causes the warm,
dense surface water to mix downwards, circulating the cooler water
towards the surface and equator.
3
Adjacent air and land: Oceans have the ability to absorb and
release heat at a much slower rate than land. As a result, coastal
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areas tend to experience moderated temperatures, while inland zones
experience diurnal and seasonal temperature extremes.
4
Water vapour: Energy from the sun can result in the evaporation of
moisture from the surface of the oceans. Water vapour plays a
significant role in the greenhouse effect.
5
Carbon: Oceans have the ability to absorb and store carbon from the
atmosphere, and release it back into the atmosphere. Carbon is
distributed unevenly throughout the oceans of the world owing to
various factors.
More than double the amount of carbon dioxide can be dissolved in
cold polar waters than in warm equatorial waters, and ocean water at
great depths contains more carbon dioxide than at the surface.
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5
Oceans at the poles tend to be deep so, as the cooled water becomes
denser, it descends, taking with it the carbon dioxide from the
surface.
Therefore, warm ocean currents such as the Gulf Stream, which
contain less carbon dioxide, circulate towards the poles. As they cool,
they take up more carbon dioxide. On cooling further, they become
denser and eventually descend into the depths. They then circulate
back towards the equator, return to the surface and are warmed
again.
At the surface of these tropical waters, carbon dioxide is released
back into the atmosphere.
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