Transcript sce13-ocean-circulation

Global circulation and ocean currents
Could underwater turbines be used to produce electricity?
Unit Objectives
• To describe and illustrate global surface and
deep water circulation distribution
• To describe the role of oceans in the global
transport of energy from the equatorial zone to
the poles.
• To describe attributes of the oceans that
facilitate the transport of energy.
• To describe changes in the polar regions that
are being discussed in regards to climate
change.
(Kelvin)
(Ammonia)
Ocean currents – surface and deep sea
(thermohaline) currents
• Ocean currents exist at several levels in the ocean.
Surface currents, mid-level currents and deep sea currents.
• Ocean currents help circulate the Sun’s heat and nutrients
to sustain life on land and in the oceans.
• Approximately half of the net transfer of energy from the
equatorial area to the poles is done by the surface and deep
water ocean currents.
• Surface currents are driven by the global winds, while
deep water currents are directed by density differences,
gravity, friction and the shape of the ocean basin.
Facts about the oceans
• 71% of the earth is covered with water. 81% in the southern hemisphere
and 61% in the northern hemisphere.
• The mean oceanic depth is 4,000 metres and the Mariana’s Trench in the
Pacific reaches 11 km.
• Ocean currents help circulate the Sun’s heat and nutrients to sustain life on
land and in the oceans.
• Heat transfer involves both sensible (via conduction and convection) and
latent heat (via changing states of water).
• Mid-latitude oceans, in particular, take up carbon dioxide, accounting for
about one quarter of the carbon dioxide emitted by human activity,
contributing to ocean acidification. The increased temperatures and the
acidification of the oceans is thought to be responsible for the diminished
coral growth in the seas.
• Ocean gyres rotate clockwise in the northern hemisphere and
anticlockwise in the southern hemisphere.
• Average ocean temperature is 3.8°C; average surface temperature is
16.1°C; average land temperature is 8.5°C.
• Water movement in the deep ocean is slow, so ocean circulation may take
1,000 years or more.
Surface Ocean currents are confined to basins
and the circulation within the basin is called a
gyre.
Global distribution of surface ocean currents
A more detailed look
at the North Atlantic
Drift which is so
important for the
climate of the British
Isles. The Gulf
Stream is about 100
km wide and 800 to
1,200 metres deep.
Water temperature
off of Florida is
about 21°C
decreasing to about
8°C off of Scotland.
Thermohaline deep ocean circulation,
the global conveyor belt.
• “Thermo” as in temperature and “haline” as in salt. The
appropriate term as these deep currents are driven by
temperature and salt which together determines their
density.
• Cold and salty water is denser than warm and freshwater,
so it tends to sink. Those differences are the main driver of
the “conveyor belt.”
•Cold water sinks at the north pole and circulates to the
south pole and after moving through the Pacific and Indian
Ocean basins returns to the north pole.
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Global ocean conveyor belt videos on
Youtube
The Global Conveyor Belt
https://www.youtube.com/watch?v=L9zjmC8InKA
The great ocean conveyor
https://www.youtube.com/watch?v=SdgUyLTUYkg
NASA | The Ocean: A Driving Force for Weather and Climate
https://www.youtube.com/watch?v=6vgvTeuoDWY
NASA | Dynamic Earth
https://www.youtube.com/watch?v=ujBi9Ba8hqs
NASA | Perpetual Ocean
https://www.youtube.com/watch?v=CCmTY0PKGDs
Thin Ice: the Southern Ocean - Thermohaline circulation
https://www.youtube.com/watch?v=vGBaL3udkHI
Aquarius: One Year Observing the Salty Seas - Ocean Salinity &
Climate
• https://www.youtube.com/watch?v=R0DIgH6yoOI
Global deep ocean conveyor belt
Why is the salinity high in the green areas on the
map?
Global ocean conveyor belt, polar view
Free floating monitoring instruments
Deep ocean monitoring devices
And now let us pause for some climate
change information
Oceanic interactions involving carbon. Carbon dioxide is a
major topic in the climate change discussion. A cursory
look indicates it’s complicated.
The trend of the Arctic sea ice extent in
September 1979 - 2012
In addition sea ice has thinned. Between the 1970s and the 2000s the seas
ice has gone from 3.1 metres to about 1.5 metres and the percentage of old
ice has decreased. Sea normally starts to expand in October.
Why hasn’t the ice in Antarctica decreased ? Think back
about the difference between the physical characteristics
of the opposing pole areas.
How land-sea configurations influence the
ocean currents and the winds around the poles
The above illustrates surface conditions, notice the winds cross the
isobars at a 45 degree angle.
Pressure at 500 mb,
The winds at this
height would be
geostrophic, parallel
to the isobars. Also
the upper
atmosphere low
pressure cell would
be reversed on the
surface, in other
words, a high
pressure cell at the
surface.
Global ocean conveyor belt, polar view
Ocean circulation web site
• https://earth.nullschool.net/#current/wind/isobaric/500hPa/orth
ographic
• Particularly interested in looking at the circulation around the
south and north pole.
Summary
• Global surface and deep water circulation assists in the
transport of energy from the equatorial region to the poles
• Water has particular qualities that facilitate the transport
of energy.
• Conduction, convection, and latent heat are mechanisms
that provide for the transport of energy within the oceans.
• Surface ocean currents are driven by the prevailing winds.
• Temperature and salinity are important factors in the
composition and direction of the deep water conveyor
belt.