Notes on “Ocean Currents”

Earth/Space

S.W.B.A.T.

• Explain how winds and the Coriolis effect influence surface currents

• Discuss the temperatures of coastal waters

• Describe density currents and how they affect Earth

Surface Currents

• Ocean currents are like rivers within the oceans

• Surface Currents - water that moves horizontally or parallel to Earth’s surface by wind

Surface Currents

• Only a few hundred meters of surface water is moved

• Some seeds and plants are carried between continents by surface currents

Major Surface Currents of Earth’s Oceans

Surface Currents

• Because Earth rotates west to east surface winds causes water to shift

• Coriolis Effect - shifting of winds & waters due to Earth’s rotation

Surface Currents

• Wind and surface currents will deflect to the right (or “clockwise”) in the northern hemisphere and to the left (counter-clockwise) in the southern hemisphere

Coriolis Effect or “Force”

Video (2:12) “Coriolis Effect Explained”

Surface Currents

• Gulf Stream – flows up the U.S. east coast and keeps Britain & Northern Europe’s climate mild

• The Gulf Stream is the world’s most powerful ocean surface current

Surface Currents

• Satellites can track currents based on ocean temperature

• Surface currents can also be tracked by using messages in bottles and other flotation devices

Ocean Surface Temperatures - Satellite Data

Surface Currents

• Warm currents (red) originate near the equator and flow towards the poles

• This distributes heat into the atmosphere and influences climate

• Cold currents (blue) flow towards the equator & heats up creating a cycle

Upwelling

• Upwelling occurs when deep, cold ocean water is brought to the surface

• Winds along some coasts will move warm water away from the surface

Upwelling

• Cold bottom water will rise up to take the place of the warmer water

• This water contains organisms that have died, sank to the bottom and decayed

• Nutrients from upwelling attract fish

Areas of Upwelling (in Red) and Major World Fisheries

Density Currents

• Density currents – when a mass of seawater circulates because of density differences

• Density increases with higher salinity• Density also increases with a decrease in

temperature• Also known as “thermohaline” currents

(“thermo” = temperature; “haline” = salinity)

Density Currents

• Changes in temperature and salinity work together to create density currents

• These currents move very slowly and can take many years to circulate

Density Currents

• Global Ocean Conveyor Belt – starts in the winter in the arctic regions

• Seawater freezes leaving behind high-salinity water that sinks

• This deep-ocean conveyor belt takes about 1000 years to circulate the Earth once!

Deep-Water Global Ocean Conveyor Belt

Video (2:40) “Ocean Odyssey: Density Current

”

Density Currents

• Mediterranean water is very high in salinity due to a warm climate and evaporation

• This causes an intermediate layer to form on top of the cold water in the Atlantic

Density Currents

• Thermohaline (density) currents are very important in replenishing nutrients from warmer surface waters

• These currents also help in regulating global climate

• Global warming may affect density currents causing further climate change

Class Activity

• A river flows into the ocean• Predict what will happen to this

layer of fresh-water• Explain your prediction