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Ocean Currents Why did Dory and Nemo’s Dad need currents?
Ocean Currents
Why did Dory and Nemo’s Dad need currents?
Why are currents important?• They provide an efficient way to move material from one
place to another.
• They transport nutrients, organisms and other biological and chemical constituents that are important for sustaining ocean life.
• Currents also involved with gas exchanges, especially O2 and CO2
• For humans, understanding current patterns improve search and rescue operations, helps to track oil spills and other pollutants, aids in ship routing to save fuel and supports fishery management.
• Ocean Current – Large scale horizontal flow of ocean water
that is persistent and driven by atmospheric circulation.
What is a current?
Ocean Currents
There are two types of ocean currents:1. Surface Currents: are wind driven and
affect about 10% of the ocean water, but cover the entire ocean surface.
2. Thermohaline Currents: (heat/salt) = density driven currents. They occur deeper in the ocean and affect ~ 90% of the ocean water.
Hot/Cold Currents
• Warm Currents: Gulf Stream, Alaskan, Kuroshio, Brazil, South Equatorial, North Equatorial, East Australian, North Atlantic, North Equatorial, East Australian
• Cold Currents: West Wind Drift, Humboldt, California, Canary, Bengula, West Australian, Labrador, Gulf Stream,
Factors that affect ocean currents:1. Solar Heating2. Winds3. Gravity/amount of
salt4. Coriolis
Surface currents• Surface currents result from winds.
• Surface currents travel until they strike an object such as a continent
• Surface currents are deflected when they strike land masses
Winds and surface water
• Wind blowing over the ocean can move it due to frictional drag.
• Wind acts only on the surface water layer.• This layer will also drag the underlying
water, but with less force.• Consequently, the speed decreases
downward.
1. Solar HeatingSolar heating causes water to expand.
Near the equator the water is about 8 centimeters higher than in middle latitudes. This cause a very slight slope and water wants to flow down the slope.
2. Wind
Winds blowing on the surface of the ocean push the water. Friction is the coupling between the wind and the water's surface.
• A wind blowing for 10 hours across the ocean will cause the surface waters to flow at about 2% of the wind speed.
• Water will pile up in the direction the wind is blowing.
3. Gravity
Gravity will tend to pull the water down the "hill" or pile of water against the pressure gradient.
4. Coriolis Effect• This effect is caused by the
rotation of the Earth.
• Winds blow at an angle to the equator (northeast to southeast).
• Winds in the northern
hemisphere blow to the right and winds in the southern hemisphere blow to the left.
Trade Winds
• Ground-level winds that flow toward the equator and are deflected by the rotation of the Earth. This deflection is the Coriolis Effect.
Prevailing Westerlies
• Winds that occur between 30 and 60 degrees latitude.
• The air moves towards the poles and appears to curve to the east. Winds originate in the west and travel east.
• These winds are responsible for many of the weather movements across the US and Canada
Coriolis continued…The rotation of the earth
creates large mounds of water that circulate and flow in a particular pattern. These mounds and flows are called Gyres. They produce large circular currents in all the ocean basins.
• Note how the North Atlantic Gyre is separated into four distinct currents,
1. North Equatorial Current
2. Gulf Stream3. North Atlantic
Current 4. Canary Current.
The Gulf Stream• Together with its northern extension towards Europe, the
North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current
• Originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean.
• At about 30°W, 40°N, it splits in two, with the northern stream crossing to northern Europe and the southern stream re-circulating off West Africa.
• The Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe.
• Typically, the Gulf Stream is 80–150 km wide and 800–1200 m deep. The current velocity is fastest near the surface, with the maximum speed typically about 2 m/s.
• The Gulf Stream carries salt into the high latitude North Atlantic where the water cools. The cooling and the added salt cause the waters to sink in the Norwegian Sea. This is the formation of Atlantic Deep Water
Deep Water Circulation
Deep waters are "formed" where the air temperatures are cold and where the salinity of the surface waters are relatively high. The combinations of salinity and cold temperatures make the water denser and cause it to sink to the bottom.
Ocean CurrentModel
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Gyres
• These currents are deflected by the continents and driven by surface winds, causing them to bend and create large current loops called circulation gyres.
• The centers often collect floating mats of seaweed and garbage. (Sargasso Sea and the N. Pacific gyre garbage patch.)
The key variables that affect water density:
1. Temperature: Denser water sinks (cold), less dense water rises (warm)
Cold-water currents occur as the cold water at the poles sinks and slowly moves toward the equator, and opposite for warm water.
2. Salinity – Saltier water = more dense, therefore sinks
“The Great Conveyor Belt”• A global "conveyor belt" is set in motion
when cold water forms in the Northern 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.
Conveyor Belt
