Transcript Ocean Currents

Ocean Circulation
Ocean Circulation
• Key Points:
– I can discuss the importance
of ocean circulation.
– I can describe the circulation
of wind in a non-rotating vs. a
rotating Earth.
– I can discuss the physical
properties of the atmosphere.
– I can begin to understand the
Coriolis effect.
Why is Ocean Circulation
Important?
• Transport ~ 20% of
latitudinal heat
– Equator to poles
• Transport nutrients and
organisms
• Influences weather and
climate
• Influences commerce
Non-rotating Earth
Convection
cell model
Add rotation and add landmasses
unequal heating and cooling of the Earth
You Tube Link
YouTube Link #2
Physical properties of the
atmosphere: Density
• Warm, low density
air rises
• Cool, high density
air sinks
• Creates circularmoving loop of air
(convection cell)
Physical properties of the
atmosphere: Water vapor
• Cool air cannot hold much water
vapor, so is typically dry
• Warm air can hold more water
vapor, so is typically moist
• Water vapor decreases the density
of air
Physical properties of the
atmosphere: Pressure
The Coriolis effect
http://www.youtube.com/watch?v=Wda7azMvabE
http://www.youtube.com/watch?v=i2mec3vgeaI
http://www.youtube.com/watch?v=XiYs4QBWTOo
• The Coriolis effect
– Is a result of Earth’s rotation
– Causes moving objects to follow
curved paths:
• In Northern Hemisphere, curvature
is to right
• In Southern Hemisphere, curvature
is to left
– Changes with latitude:
• No Coriolis effect at Equator
• Maximum Coriolis effect at poles
The Coriolis effect on Earth
• As Earth rotates,
different latitudes
travel at different
speeds
• The change in
speed with
latitude causes
the Coriolis effect
Ocean Currents
• Recap Key Points:
– I can discuss the importance
of ocean circulation.
– I can describe the circulation
of wind in a non-rotating vs. a
rotating Earth.
– I can discuss the physical
properties of the atmosphere.
– I can begin to understand the
Coriolis effect.
Ocean Currents
• Key Points:
– I can describe how the
Coriolis effect influences
surface winds.
– I can explain the difference
between factors affecting
surface circulation vs. deep
ocean circulation.
– I can describe oceanic gyres
& their rotations.
A)
B)
Idealized winds generated by pressure gradient and Coriolis Force.
Actual wind patterns owing to land mass distribution..
http://www.youtube.com/watch?v=aeY9tY9vKgs&feature=youtube_gdata_player
Ocean Currents
Surface Currents
The upper 400 meters of the ocean
(10%).
Deep Water Currents
Thermal currents (90%)
Surface Currents
Forces
1. Solar Heating (temp, density)
2. Winds
3. Coriolis
Wind-driven surface currents
Current Gyres
Gyres are large circular-moving loops of water
Five main gyres (one in each ocean
basin):
• North Pacific
• South Pacific
• North Atlantic
• South Atlantic
• Indian
• Generally 4 currents in each gyre
• Centered about 30o north or south
latitude
Surface and Deep-Sea Current
Interactions
Unifying concept: “Global Ocean Conveyor Belt”
http://www.youtube.com/watch?v=6vgvTeuoDWY
http://seis.natsci.csulb.edu/rbehl/ConvBelt.htm
Heat Transport by Currents
• Surface currents transport heat energy
from equator towards the poles
• Currents also involved with gas
exchanges, especially O2 and CO2
• Nutrient exchanges important within
surface waters (including outflow from
continents) and deeper waters
(upwelling and downwelling)
• Pollution dispersal
• Impact on fisheries and other resources
Global ocean circulation that is driven by differences in
the density of the sea water which is controlled by
temperature and salinity.
White sections represent warm surface currents.
Purple sections represent deep cold currents
Ocean Currents
• Recap the Key Points:
– I can describe how the
Coriolis effect influences
surface winds.
– I can explain the difference
between factors affecting
surface circulation vs. deep
ocean circulation.
– I can describe oceanic gyres
& their rotations.
Ocean Currents
• Key Points:
Upwelling and downwelling
Vertical movement of water ()
– Upwelling = movement of deep water to
surface
• Hoists cold, nutrient-rich water to surface
• Produces high productivities and abundant
marine life
– Downwelling = movement of surface water
down
• Moves warm, nutrient-depleted surface water
down
• Not associated with high productivities or
abundant marine life
upwelling
downwelling
Satellite Observations
• TOPEX/Poseidon, Jason 1, and other
satellites have observed patterns of
change over the past few years
• Animation of seasonal and climaticallyinfluence shifts available at
http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/MOVIES
/Topex_Dynamic_Ocean_Topography.mpg
El Niño-Southern Oscillation
(ENSO)
• El Niño = warm surface current in
equatorial eastern Pacific that occurs
periodically around Christmastime
• Southern Oscillation = change in
atmospheric pressure over Pacific
Ocean accompanying El Niño
• ENSO describes a combined oceanicatmospheric disturbance
El Niño
• Oceanic and atmospheric
phenomenon in the Pacific Ocean
• Occurs during December
• 2 to 7 year cycle
Sea Surface Temperature
Atmospheric Winds
Upwelling
Normal conditions in the
Pacific Ocean
El Niño conditions (ENSO
warm phase)
La Niña conditions (ENSO
cool phase; opposite of El
Niño)
Non El Niño
El Niño
1997
Non El Niño
upwelling
El Niño
thermocline
El Niño events over the last 55 years
El Niño warmings (red) and La Niña coolings (blue) since
1950. Source: NOAA Climate Diagnostics Center
World Wide Effects of El Niño
• Weather patterns
• Marine Life
• Economic resources
El Nino Animation
http://esminfo.prenhall.com/science/geoanimations/ani
mations/26_NinoNina.html
Effects of severe El Niños
Inquiry
1. What is a convection cell?
2. Which direction do currents get deflected in
the Southern Hemisphere?
3. What depth should the water be for an Ekman
spiral to occur?
4. How are surface currents created?
5. What is a gyre?
6. How can an El Nino impact upwelling?
7. Coriolis Effect is strongest near the _____?