Ocean Currents

Two TypesOcean currents are divided into two types:

Surface currents, which are driven by the windDeep ocean currents, which are driven by density

Surface CurrentsGlobal winds flow in a regular pattern that varies with latitude. These patterns are:

Location Direction of Wind

Tropics EasterlyTemperate Westerly

Polar Easterly

Surface Currents, cont’dThese large scale wind patterns exert a frictional drag and set the surface waters (down to ~400m) of the oceans in motion, forming currents.

These currents are deflected by the continents, causing them to bend and create large current loops called circulation gyres in all the oceans.

Circulation of the gyres is clockwise in the Northern Hemisphere and anticlockwise in the Southern Hemisphere, due to the Coriolis Effect.

Coriolis Effect VideosVideo Example Iceland Volcano Eruption

Circulation Gyres

Surface currents carry heat from the tropics to higher latitudes, transferring the heat to the air and regulating temperatures worldwide.

Note: Wind direction indicates where the wind is coming from (a westerly wind is blowing from the west). Water direction indicates where the current is flowing to (a westerly current is flowing to the west).

Recap of key concepts…What are the two types of currents?What force(s) drive surface currents?What force(s) drive deep ocean currents?What are Circulation Gyers?How is a Gyer created?Coriolis Effect

Measuring Surface CurrentsOceanographers use drifters to measure the speed and direction of currents.This info is used to predict:

where oil spills would goweather patterns (hurricanes)iceberg danger zoneswhere drifting organisms came from

DrifterThe float is equipped with sensors that measure temperature, pressure, salinity, submergence and

light.The drogue just ensures the drifter moves with the ocean currents and not the wind and waves.

Deep Ocean CurrentsDensity of ocean water depends on 2 variables:

Temperature – the colder the water, the more dense. The thermocline acts as a density boundary.Salinity – the saltier the water, the more dense. The halocline also acts as a density boundary.

Bottom waters are rich in nutrients because decomposition of dead creatures releases nitrogen and phosphorus.The two density boundaries prevent cold, nutrient-rich bottom water from mixing with warm, surface water.This limits the growth of plants, and also the animals that feed on them.

UpwellingIs a term that is used to describe nutrient-rich bottom waters moving up to the surface.Where upwelling occurs, areas are much more productive.One of the world’s richest fishing grounds off the coast of Peru is caused by upwelling.

Causes of Upwellingmovement of surface waters away from a coastline. This water is replaced by bottom water.surface cooling in the fall. Surface waters cool due to cooler air temps, become more dense, and sink. This pushes bottom water upwards.winter storms, which mix water.

Recap…Why would we want to measure surface currents?What is upwelling and how can it happen?What is a major benefit of upwelling?

El NiñoHappens every 3-8 yearsThe winds across the tropical Pacific reverse their direction. This prevents upwelling and causes the collapse of fisheries off the coast of PeruIt also upsets weather patterns globally.

Videohttp://www.youtube.com/watch?v=uySu7Zv2cbU

EL NINO – Think/Pair/Share

Explain EL NINO in your own words.

Ocean Currents Activity

Colour the currents discussed as either warm or cold and answer questions attached.

AssignmentComplete the Nike shoes Assignment using the following map of the pacific ocean (next slide) and answer the questions on the question sheet.Remember:

Latitude = N/S from 0 to 90Longitude = E/W from 0 to 180

E E E E E W W W W W

N

S

Extensions

• The recent tsunami which hit Fukishima, Japan dispersed a lot of debris into the Pacific Ocean. From your knowledge of the North Pacific currents and the Nike Shoes, predict where and when this debris might show up in about a year.

Research Questions – 15 minutes

• What is the Great Pacific Garbage Patch?• What is causing it?• What can we do about it?

What did we find out?