Ocean currents exist to help balance the Earth's uneven heating by the Sun. The Sun deposits most of its energy at the equator, so atmospheric circulation and ocean currents transfer heat from the equator toward the poles. Winds drive 80% of this redistribution, while ocean currents account for 20%. Surface ocean currents form circular gyre patterns in ocean basins, driven by subtropical high pressure systems, and affect the locations of deserts on western continents in the Southern Hemisphere. Deep ocean currents also circulate heat but over much longer timescales of around 1,000 years.
2. What can we interpret from the
following global map?
3. How does ocean currents try to
balance the Earth’s energy budget?
4. 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.
5. 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.
7. Surface Oceanic Circulation Notice
circulatory
cells or
‘gyres’.
Driven by
subtropical
high pressure
systems.
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?
9. ‘Global ocean
conveyer belt’, or
deep
ocean currents
Begins here.
BBC Wild Weather
- Wet –
Ocean Circulations
9 min10 to12 min12
These travel at a much slower speed than surface currents and are driven by
differences in the density of seawater. Density is affected by differences in
temperature and salinity. One complete circuit, as shown above, is
estimated to take about 1,000 years!
10. How can we connect ocean currents to the
balancing of Earth’s energy budget?
11. We can refer to global atmospheric
circulations and ocean currents as factors
that influence global climates.
Can you think of two other factors?
12. 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
13. 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….
14. Altitude
1. Environmental Lapse Rate (ELR)
– 6.5oC per 1000m (does vary seasonally)
1. Dry Adiabatic Lapse Rate (DALR)
– 10oC per 1000m
1. Saturated Adiabatic Lapse Rate (SALR)
– 5oC per 1000m
Lapse Rate Exercise
15. 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