Ocean Currents

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Ocean Currents

• Earth and Space Science

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Seawater Temperature, Salinity and Density

• Ocean waves carry matter and energy
• This thermal energy can be transferred to the
  air, and to the land.
• There are multiple layers in the ocean
• There are multiple densities of water in the
  ocean
• The oceans salinity is not uniform

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Currents

• Water in oceans can sink, rise, and flow
  horizontally

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• A. Ocean currents predominantly horizontal
  movement of ocean water
• Carry energy and matter from one part of the
  ocean to another

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• Can be local or very broad
• May flow just on the surface ? Surface current
  (very fast)

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• May flow in deep water ? slower but much thicker
  layer
• Movement of deep ocean water is controlled by
  water density

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B. Density is determined by 2 factors

• 1. Temperature
• The sun does not warm the ocean water evenly

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Ocean Surface Temperture
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B. Density is determined by 2 factors

• Cold water is more dense and sinks
• Warm water is less dense and stays at the surface

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B. Density is determined by 2 factors

• 2. Salinity
• Concentration of dissolved salts in the seawater
• Expressed as parts per thousand
• Approximately 35 parts per thousand (35 g salts
  per 1000 g water)
• Higher salinity higher density

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B. Density is determined by 2 factors
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B. Density is determined by 2 factors

• Surface water can change in density by changing
  salinity due to excess rain or increased
  evaporation or where rivers enter the ocean

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II. Water Masses

• The ocean is a single body of water but is not
  the same everywhere
• Temperature and salinity vary
• from place to place
• Water Mass a large region of water within the
  ocean that is about the same temperature and
  salinity

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A. Surface layer

• Winds mix the water vertically so temperature and
  salinity remain relatively constant through the
  first 100m-200m of depth

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B. Deep layers

• No vigorous mixing, thus water masses retain
  distinctive properties

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• C. Water masses are named for the location where
  they are formed
• Examples Antarctic Bottom Water
• North Atlantic Deep Water
•  

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• D. Water masses sink at the poles and move along
  the ocean floor

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III. What causes the deep circulation?

• A. Giant convection cells
• ?Convection
• is the
• rising and
• falling of
• heated and
• cooled fluids
• due to
• changing
• density

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• B. How does the cold deep water mix with the
  warmer surface water?
• ? Still being studied at this time, but it is
• that the movements of the tides is a
• possible cause of mixing

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IV. Surface Currents

• Extend down to depths of about 200m
• A. Surface currents flow for long distances
• across the ocean
• 1. Form gyres, which are circular cells of motion
  of the surface water

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• 2. Gyres are found in each of the major
• ocean basins
• 3. Circulate clockwise in the Northern
• 
  Hemisphere
• 4. Circulate counter-clockwise in the
• Southern
  Hemisphere

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World Ocean Currents
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• B. Gyres help transport
• energy and matter from
• low latitudes to the
• higher latitudes.

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• C. Caused by blowing winds near the Equator
• 1. Tradewinds/Easterlies at low
  latitudes/tropics
• ? Blow East to West

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• 2. Prevailing Westerlies in mid-latitudes
• ? Blow West to East

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• D. Eckman Drift horizontal movement of water
  resulting from the balance of the Coriolis effect
  and wind stress

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• 1. Causes water to move at an angle to the right
  of the general wind direction (90o)
• 2. Causes a mound of water which balances out
  the Eckman Drift
•  

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E. Upwelling

• Strong upward movement of water from the deep to
  the surface

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E. Upwelling

• 1. As water moves
• away from the coastline due to the
• Eckman Drift, more water flows up to
• replace it from deeper in the ocean.
• 2. The upward movement brings nutrient rich deep
  water to shallow areas for animals and plants to
  use

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E. Upwelling
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E. Upwelling
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E. Upwelling

• 3. Nutrients come from the rain of dead
  organisms from the warmer surface layer
• 4. Deep circulation moves the nutrients around,
  and then upwelling generally moves the nutrients
  to the eastern sides of ocean basins.
• 5. Most fisheries are supported by this upwelling
  of nutrients.

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F. Downwelling

• Downward motion of surface water to the deep
  ocean

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F. Downwelling