Ocean Currents

Year 13

What can we interpret from the following global map?

How does ocean currents try to balance the Earth’s energy budget?

Definitions:• An ocean current can be defined as a

horizontal movement of unusually cold or warm surface water, to a depth of 100m.

• Ocean currents are driven by the circulation of wind above surface waters. Frictional stress at the interface between the ocean and the wind causes the water to move in the direction of the wind.

Ocean currents: why do they exist?

• The sun’s energy is not distributed evenly; it is most concentrated upon the equator.

• Atmospheric circulation and ocean currents exist as a means of transferring heat away from the equator and towards the polar regions.

• Winds account for 80% and ocean currents for 20% of this redistribution.

Surface Oceanic Circulation

Desert regions are located towards the western side of continents, particularly in the Southern Hemisphere. Look at the map of global ocean currents above and your mapped desert locations – what do you notice?

Surface Oceanic CirculationNoticecirculatory cells or ‘gyres’.

Driven by subtropicalhigh pressuresystems.

The movement of sea water in the South Pacific

These travel at a much slower speed than surface currents and are driven bydifferences in the density of seawater. Density is affected by differences in temperature and salinity. One complete circuit, as shown above, isestimated to take about 1,000 years!

‘Global ocean conveyer belt’, or

deep ocean currents

Begins here.

BBC Wild Weather

- Wet –

Ocean Circulations

9 min10 to12 min12

How can we connect ocean currents to the balancing of Earth’s energy

budget?

We can refer to global atmospheric circulations and ocean currents as

factors that influence global climates.

Can you think of two other factors?

Latitude

• Length of daylight– Compare the tropics to

the poles

• Angle of incidence– ‘Height’ of the sun in the

sky

Further reading: p. 43 in AQA Textbook

Altitude

Temperatures decrease with height above sea level

Adiabatic Lapse Rate……temperature change with height for a parcel of air that has no exchange of heat or moisture with the air surrounding it

There are three types of lapse rates….

Altitude

1. Environmental Lapse Rate (ELR)– 6.5oC per 1000m (does vary seasonally)

2. Dry Adiabatic Lapse Rate (DALR)– 10oC per 1000m

3. Saturated Adiabatic Lapse Rate (SALR)– 5oC per 1000m

Lapse Rate Exercise

Activity

Account for the likely reasons behind the temperature differences recorded on the same day for the paired locations:

1. Berlin -13oC, Amsterdam -3oC in January

2. London 24oC , Hull 17oC in August

3. Cape Town 22oC , Stockholm -1oC in December

4. Aspen -2oC , Denver 2oC in February

5. Halifax (Canada) -4oC , Penzance 8oCin January