Investigating Ocean Dynamics
Ocean Dynamics
The oceans, like the atmosphere, are
composed of a fluid.
Similar physics principles operate in the
oceans and atmosphere.
Ocean currents occur because of:
Winds that move surface waters and
generate surface currents
Temperature differences in surface and
deep sea waters that generate thermal
currents
Salinity differences that generate
density currents
Tidal forces that move water
Surface Ocean Currents
A large scale circular pattern in the
ocean water motion is called a gyre.
There are several large gyres in the
world’s oceans.
Large Ocean Gyres
World Ocean Currents
Currents generated by differences in salinity (density)
and temperature are called thermohaline circulation.
http://www.sunke-schmidt.de/flash/flash/circulation_en.html
http://www.youtube.com/watch?v=3niR_-Kv4SM
http://www.cru.uea.ac.uk/cru/info/thc/
El Nino
El Nino is also called the "El Nino-Southern
Oscillation" or ENSO. The name El Nino originally
came from fisherman off the coast of South
America who noticed the unusually warm ocean
current in December. El Nino means "The Little
One," or the infant Jesus in Spanish. The
fisherman gave the warm water this name
because it shows up off the coast of South
America around Christmas.
El Nino
El Nino is a disruption of the ocean-atmosphere
pressure system in the eastern Pacific Ocean
which causes significant global weather
changes. Among these changes are drought in
the West Pacific, which sometimes leads to
destructive brush fires in Australia, and
increased rainfall across the southern part of the
US and Peru, which has caused flooding.
El Nino
El Nino events occur irregularly, approximately every two
to seven years. El Nino is characterized by unusually warm
ocean temperatures along and on both sides of the
equator in the eastern and central Pacific and by a
decrease, or sometimes a reversal of the trade winds.
During El Nino, the winds at the equator blow from west
to east in the Pacific, bringing warm surface water to the
western coasts of North and South America.
Under normal conditions,
strong easterly winds cause
cold nutrient-rich waters to rise
along the South American
coast. The cold water brings up
nutrients that attract fish.
The weaker winds in an El Nino
event prevent the cold water
upwelling and the ocean heats
off the coast of South America.
The water is less nutrient-rich.
Sea Surface Temperature Animation for 1997-1998
El Nino Event
http://www.cdc.noaa.gov/map/clim/sst_olr/old_s
st/sst_9798_anim.shtml
Ocean Waves are generated
by:
Winds
Undersea or land-based disturbances
(such as earthquakes)
Tidal forces
Changes in underwater terrain
When a wave passes, particles
move vertically because of the
forces acting on them.
Waves have features…
Ocean waves are related to wind speed
Data from
TOPEX/Poseidon Mission
NASA
As waves approach a shore they
become “breakers” because the
same amount of water must occupy
a smaller volume.
1 Destructive wave (plunging breaker)
2 Constructive wave (spilling breaker)
a Steep shingle beach
b Swash
c Backwash
d Gentle sandy beach
3 Sand and shingle beach
3a Sand
3b Rock
3c Shingle
3d Cliff
3e Storm beach
3f Beach cusps
3g Drainage channels
3h Sand ripples
3i Sand ridge
3j High tide
3k Low tide
Citation information
Text: "Coastal deposition 1: waves and beaches." in Earth
Science On File. Revised Edition. New York: Facts On File, Inc.,
1999. Facts On File, Inc. Science On-line. <www.factsonfile.com>.
Image: "Coastal deposition 1: waves and beaches." Copyright
Diagram Visual Information Ltd., 1999. Facts On File, Inc. Science
On-line. <www.factsonfile.com>.
1 Longshore drift
1a Prevalent wave direction
1b Sand or shingle moved by
swash
1c Sand or shingle moved by
backwash
2 Effect of groyne
2a Prevalent wave direction
2b Accumulating sand or shingle
2c Direction of drift
3 Bay beaches
3a Prevalent wave direction
3b Headlands
3c Bays
Tides
The cyclic rise and fall of ocean levels
based on gravitational forces.
Can be high and low
Height of high and low tides varies
based on lunar phases and proximity of
the Earth to the Moon and Sun
Tides
When the Sun, Moon,
and Earth are aligned, the
gravitational pull on the Earth
is greatest and water levels
respond by rising.
The highest tides occur at the
New Moon and the next
highest at the Full Moon.
These are called spring tides.
When the Moon is at right
angles to the Sun and Earth,
the pull is less and the tides
are lower. These are termed
neap tides.