Ocean Currents

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Ocean Currents
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Currents

• Currents are moving masses of water
• Ocean currents transport nutrients, heat and
  water, acting like the circulatory system of the
  ocean
• Currents influence climate and living conditions
  for plants and animals, in water and on land.

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Gyres

• Currents are deflected by the continents which
  cause them to bend and create large current loops
  called circulation gyres.
• The Main Gyres include
• North Pacific Gyre
• South Pacific Gyre
• North Atlantic Gyre
• South Atlantic Gyre
• Indian Ocean Gyre
• Ross Sea Subpolar Gyre

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Gyres of the World
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Gyres

• Within these gyres are the ocean currents of the
  world
• The Coriolis effect (due to the rotation of the
  Earth) move water clockwise in the Northern
  Hemisphere and counter-clockwise in the Southern
  Hemisphere

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Coriolis Effect

• Causes a surface water movement at 45 to the
  direction of the wind
• This movement is called Ekman Transport
• Each layer in the water moves at 45 to the
  above water layer
• The deepest layers of the ocean will move in the
  opposite direction of the wind due to the Ekman
  Transport

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Surface Currents

• The horizontal circulation of ocean waters are
  called surface currents.
• About 10 of the world ocean is involved in
  surface currents
• Surface currents is driven by wind friction which
  moves water at a depth of about 450 m

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Surface Currents

• The winds that most affect the oceans' currents
  are
• The Westerlies which blow west to east in the
  temperate regions (30-60 latitude)
• The Trade Winds which blow east to west at 15
  latitude
• The Easterlies which blows east to west in the
  polar regions (60 - 90 latitude)

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Surface Currents impacted by Westerlies and Trade
Winds

• The currents impacted by the Westerlies and Trade
  Winds are the fastest and deepest currents
• These currents are moving the warm water north
• There are 5 large warm currents
• The largest current is the Gulf Stream
• It moves at 2 m/s at a depth of 450 m
• It can travel up to 160 km/day

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Surface Currents by the Equator

• Currents around the equator (impacted usually by
  Trade Winds) are accompanied by countercurrents
  and undercurrents
• Countercurrents are currents flowing on the
  surface in the opposite direction
• Undercurrents are currents flowing in the
  opposite direction but under the surface currents

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Surface Currents impacted by Easterlies

• These currents contain colder water from the
  polar regions to the equator
• There are 5 main cool currents
• They are shallow and very broad (sometimes up to
  1000 km in width)
• Slow surface flow compared to westerly currents
• Ex. Canary Current flows at 1 m/s compared to the
  Gulf Stream at 2 m/s

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Deep Ocean Currents and Thermohaline Circulation

• Differences in water density affect deep ocean
  currents
• Movement of surface ocean water to the bottom of
  the ocean and movement of deep ocean water to the
  surface.
• It is impacted by temperature and salinity
• It is responsible for vertical movement and
  circulation of oceans

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Thermohaline Circulation

• Upwelling
• When nutrient- rich water from the bottom of the
  ocean moves up to the surface.
• Downwelling
• When the water from the surface of the ocean
  moves downward

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Global Conveyor Belt

• An example of Thermohaline Circulation occurs
  when deep water forms in the North Atlantic and
  sinks because of density
• It starts to moves south, and circulates around
  Antarctica, and then moves northward to the
  Indian, Pacific, and Atlantic basins.

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Other causes of currents

• Include tides, rain, runoff, and ocean bottom
  topography.
• Topography is the surface features of a place.
• Ocean topography includes slopes, ridges,
  valleys, and mountains! All these things are
  found at the bottom of the ocean, and can
  influence currents.

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How do we study currents?

• Release studies which use drift bottles or drift
  sensors (float methods)
• Flow methods are used to measure the speed of
  currents as it flows past a fixed object
• Scientists are now using CFCs to measure flow
  because they are easy to track
• Satelites are used to measure temperature,
  topography and color