Ocean Currents and Climate

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Ocean Currents and Climate
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Role of the Sun

• Over ½ of incoming solar radiation absorbed by
  ocean surface
• Thats a LOT of heat to move!

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Sea surface temperature varies mainly with
latitudewhy?
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• Solar radiation arrives at a different angle at
  the poles than at the equator.
• Area b is bigger than area a
• Beam of light is most concentrated at the equator
  
• Less concentrated towards the poles
• Earth receives more heat per unit area at the
  equator than it does at the poles

• This DIFFERENTIAL HEATING of the planet causes
  air masses to move around

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Atmospheric cells and planetary winds
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Three types of cellsThree types of planetary
winds

• Polar cell
• Mid-latitude cell
• Equatorial cell
• Mid-latitude cell
• Polar cell

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Causes of oceanic currents?
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There are two types of Ocean Currents

• 1. Surface Currents
• about 10 of all the water in the ocean.
• upper 400 meters of the ocean.
• 2. Deep Water Currents - Thermohaline Circulation
• make up the other 90 of the ocean
• move around the ocean basins by density driven
  forces and gravity.

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Primary Forces--start the water moving

• Solar Heating
• Winds
• Gravity
• Coriolis Effect

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Surface Circulation

• Solar heating causes water to expand
• 8 centimeters high at equator
• Causes a very slight slope
• Water flows downhill

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The effect of winds on the vertical movement of
water

• Winds blowing on the surface of the ocean push
  the water.
• Friction is the link between the wind and the
  water's surface.

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Surface Circulation

• 10 hours of wind blowing across the ocean causes
  surface waters to pile up in the direction the
  wind is blowing.
• Gravity will tend to pull the water down the
  "hill" or pile of water against the pressure
  gradient.

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Coriolis Effect?
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NORTHERN HEMISPHERE
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Coriolis Effect

• Earth's spin causes the wind to curve
• HIGH PRESSURE (descending air)
• Wind in the N hemisphere curves right
• Wind in the S hemisphere curves left
• LOW PRESSURE (rising air)
• Wind in the N hemisphere curves left
• Wind in the S hemisphere curves right

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Surface Circulation

• Large circular currents exist in all the ocean
  basins
• They are called GYRES

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How do gyres form?

• Remember the hill of water
• This hill is formed by the inward push of water
  through a process called Ekman Transport

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Ekman Transport

• Wind blowing over ocean has greatest effect on
  the surface.
• Coriolis Force moves objects to the right
  (northern hemisphere)
• Planet is rotating
• A lower layer moves slower than the layer above,
  relative to this rotation

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Ekman Transport

• With each successive layer down the speed is
  reduced.
• This leads to the spiral effect seen in diagram.

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Ekman Transport

• NET movement of water is 90o to the right of the
  wind direction (in the northern hemisphere).

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Combined Ekman effects set-up gyres

• and upwelling?

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PNW upwelling

• We live in the zone of WESTERLIES
• NW winds in summer
• Net surface water movement out to sea
• Upwelling water from underneath

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PNW upwelling

• Upwelling along the coast caused by Ekman
  transport of waters (waters move to the right of
  the wind).
• The waters moved offshore are replaced by waters
  from below. This brings cold, nutrient-rich
  waters to the surface.

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Downwelling in winter

• Downwelling is caused by Ekman transport onshore
  (movement of water to the right of the wind
  direction).
• WINTER phenomenon

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The California current eastern boundary current

• Broad, slow, cool, and shallow
• Eastern boundary currents are often associated
  with upwelling

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The ocean is layered

• warmer on top, cold at the bottom.
• Organisms move from one layer to another, and
  plant and animal remains containing nutrients
  "rain" down, but the layers stay fairly separate
  in all but a few places.

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Upwelling stirs the soup
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Upwelling food chain

• Humans
• Marine mammals
• Birds
• Piscivorous fishes
• Planktivorous fishes
• Plankton

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• Coastal upwelling occurs against the western
  sides of continents in the Atlantic, Indian, and
  Pacific.
• There, colder water rises to replace warm surface
  water blown out to sea by strong offshore winds.

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Upwelling supports about half of the world's
fisheries,

• though these cool waters account for only 10
  percent of the surface area of the global ocean.

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The Great Ocean Conveyor Belt
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• Near surface warm currents are drawn in red.
• Blue depicts the deep cold currents.
• Note how this system is continuously moving water
  from the surface to deep within the oceans and
  back to the top of the ocean.

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• Deep water forms when sea water entering polar
  regions cools or freezes, becoming saltier and
  denser.
• Colder or saltier water tends to sink.
• A global "conveyor belt" is set in motion when
  deep water forms in the North Atlantic, sinks,
  moves south, and circulates around Antarctica,
  and then moves northward to the Indian, Pacific,
  and Atlantic basins.
• It can take a thousand years for water from the
  North Atlantic to find its way into the North
  Pacific.
• Warm surface currents invariably flow from the
  tropics to the higher latitudes, driven mainly by
  atmospheric winds, as well as the earth's
  rotation.

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Global salinity patterns

• Why are tropical latitudes saltier?

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Density differences are a function of different
temperatures and salinity
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Next time Quirky Anomalies

• El Nino/Southern Oscillation
• Pacific Decadal Oscillation

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References

• http//earth.usc.edu/stott/Catalina/Oceans.html
• http//seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/oce
  anography_currents_1.html
• http//www.physicalgeography.net/fundamentals/8q.h
  tml
• http//amap.no/acia/
• http//www.windows.ucar.edu
• http//www.glacier.rice.edu/weather/3_atmcirc.html
  
• http//www.amastro.org/at/w/wgacs.html
• http//paos.colorado.edu/toohey/study.html
• http//www.soc.soton.ac.uk/CHD/education/posters/p
  roductivity.html