Currents

Oceans 11

Essential Questions

• What are ocean currents? • What is the purpose / role of

ocean currents?• What is the Coriolis Effect?• What are thermohaline

currents? • What are the major global

gyres?• What are the major currents

affecting Atlantic Canada?

What are ocean currents?

What is a current?

• A continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as:– breaking waves, – wind, – Coriolis force, – Temperature,– salinity differences, and – tides caused by the gravitational

pull of the Moon and the Sun.

What is a gyre?

• Gyres are any large system of rotating ocean currents, particularly those involved with large wind movements.

• Gyres are caused by the Coriolis Effect; planetary vorticity (tendency for elements of fluid to spin) along with horizontal and vertical friction.

What is the purpose / role of ocean currents?

Purpose…

• to carry heat from place to place in the Earth system

• affects regional climates

• they transport creatures around the world and affect the water temperature in ecosystems

Anomalies of Surface Currents

• Ocean Eddies– form when a bend in a surface ocean current

lengthens and eventually makes a loop, which separates from the main current.

– the swirling waters last for at least a few months – Warm water eddies are sparse in marine life

because the water does not have many nutrients– Cold water eddies are usually full of nutrients and

marine life.

• Upwelling– where water from the deep sea travels up to the

surface– often happens where wind blows along a coastline– upwelling areas are full of marine life

What is the Coriolis Effect?

Who discovered the Coriolis Effect?

• Gustave-Gaspard Coriolis – in 1835 – he was a French engineer-

mathematician

Coriolis Effect explained…

• The rotation of the Earth causes an interesting phenomena on free moving objects on the Earth.

• Objects in the Northern Hemisphere are deflected to the right, while objects in the Southern Hemisphere are deflected to the left.

• The Coriolis effect, thus tries to force winds to shift towards the right or left. The Coriolis effect can at times cause winds to blow back up the pressure gradient.

Why does this happen?

• There are two reasons for this phenomenon:– the Earth rotates eastward – the tangential velocity

(speed along a curve) of a point on the Earth is a function of latitude (the velocity is essentially zero at the poles and it attains a maximum value at the Equator)

What does the Coriolis Effect affect?

• it affects the rotation of the oceanic currents

• it affects prevailing winds and the rotation of storms

What are thermohaline currents?

How does it work?

• Thermohaline currents are driven by density differences in the water– density depends on its temperature

(thermo) and salinity (haline)

• At the earth's poles, when water freezes, the salt doesn't necessarily freeze with it, so a large volume of dense cold, salt water is left behind.

• When this dense water sinks to the ocean floor, more water moves in to replace it, creating a current.

• This current begins with the cold water near the North Pole and heads south between South America and Africa toward Antarctica, partly directed by the landmasses it encounters.

• In Antarctica, it gets recharged with more cold water and then splits in two directions -- one section heads to the Indian Ocean and the other to the Pacific Ocean.

• As the two sections near the equator, they warm up and rise to the surface as an upwelling.

• When they can't go any farther, the two sections loop back to the South Atlantic Ocean and finally back to the North Atlantic Ocean, where the cycle starts again.

Interesting details

• An underwater current circles the globe with a force 16 times as strong as all the world's rivers combined

• Moves much more slowly than surface currents -- a few centimeters per second, compared to tens or hundreds of centimeters per second.

Purpose…

• It is crucial to the base of the world's food chain:– transports water around the globe– enriches carbon dioxide-poor, nutrient-

depleted surface waters by carrying them through the ocean's deeper layers where those elements are abundant

– nutrients and carbon dioxide from the bottom layers are brought up to the surface

– allows algae and seaweed to grow

• also helps to regulate temperatures.

The Endless Voyage Series - Deep Connections -

• http://learning.aliant.net/Player/ALC_Player.asp?ProgID=INT_ENDVOY08

What are the major global gyres?

Major gyres

• North Atlantic Gyre

• South Atlantic Gyre

• Indian Ocean Gyre

• North Pacific Gyre

• South Pacific Gyre

North Atlantic Gyre

• located in the Atlantic Ocean

• contains the Sargasso Sea

• circulates clockwise

• traps man-made ocean debris in the North Atlantic Garbage Patch

South Atlantic Gyre

• the southern branch of the subtropical gyre in the south Atlantic

• circulates counter-clockwise

• this current allows Antarctica to maintain its huge ice sheet by keeping warm ocean waters away

• is the largest ocean current

Indian Ocean Gyre

• is located in the Indian Ocean

• circulates counter-clockwise

North Pacific Gyre

• located in the northern Pacific Ocean

• comprises most of the northern Pacific Ocean

• circulates clockwise• is the largest ecosystem on our

planet • an accumulation of man-made

marine debris, known as the Great Pacific Garbage Patch

South Pacific Gyre

• located south of the equator between South America and Australia

• circulates counter-clockwise

• is the Earth's biggest system of ocean currents

• it is mostly inactive and contains little marine life

What are the major currents affecting Atlantic Canada?

The currents of the North Atlantic

• The Gulf Stream

• The North Atlantic Current

• The Irminger Current

• The Labrador Current

• The Greenland Current

http://upload.wikimedia.org/wikipedia/commons/6/63/LabradorCurrentus-coastguard.jpg

The Gulf Stream

• is a powerful, warm, and swift Atlantic ocean current

• it originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean

• The Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe

• is also a significant potential source of renewable power generation

The North Atlantic Current

• is a powerful warm ocean current

• it continues the Gulf Stream northeast.

• West of Ireland it splits in two.– one branch (the Canary Current)

goes south – the other continues north along

the coast of northwestern Europe where it has a considerable warming influence on the climate.

The Irminger Current

• is a north Atlantic ocean current setting westward off the southwest coast of Iceland

The Labrador Current• is a cold current in the North Atlantic

Ocean • it flows from the Arctic Ocean south

along the coast of Labrador and passes around Newfoundland, continuing south along the east coast of Nova Scotia

• It meets the warm Gulf Stream at the Grand Banks southeast of Newfoundland and again north of the Outer Banks of North Carolina. The combination of these two currents produces heavy fogs and also created one of the richest fishing grounds in the world.

The Greenland Current

• is a weak cold water current that flows to the north along the west coast of Greenland