4. Causes of Ocean currents
Following are the causes of ocean currents :
• Solar heating
• Wind
• Gravity
• Salinity of water
• Temperature
• Coriolis effect
• Underwater earthquakes
4
5. Solar Heating
The heat energy from the sun causes water to
expand. The water around the equator is
roughly 8 c.m. high than in middle latitudes. It
causes a slight slope in the water and it flows
down the slopes. Warm water flows towards
the cold Polar Regions and cold water flows
towards the warmer equatorial regions.
5
6. Wind
• The Wind is responsible for ocean currents as
it blows the water on the surface .
• The wind is responsible for surface currents
where ocean water is redistributed based on
its density and temperature.
6
7. Gravity
Gravity tends to pull items towards the surface
of the earth. When the wind blows ocean water,
the water piles up in the direction of the wind.
Gravity, therefore, pulls the water down the
‘hill’ against the pressure gradient.
7
8. Salinity of water
• When water moves towards the poles, it gets
cold and freezes into ice, leaving a share of
salt behind. It makes the underlying water
saltier, making it denser.
• The cold, saltier and denser water sinks to
the floor of the ocean and is replaced by
surface water in the process.
8
9. Temperature
9
• Warm water tends to stay on the surface of
the ocean, while the cold water remains at
the bottom.
• When water warms up , then it becomes less
dense, so , rising to the surface of the ocean,
resulting in upwellings.
10. Coriolis effect
• Due to the earth's rotation, the direction of
the winds and ocean currents get changed.
• As the Earth rotates, the winds and the
ocean currents are deflected towards the
right in the Northern Hemisphere and
towards the left in the Southern Hemisphere.
This is known as Coriolis Effect.
10
12. Underwater earthquakes
• Occasional events such as underwater
earthquakes can a trigger serious ocean
currents by moving masses of water inland
when they reach shallow water and
coastlines.
12
13. Characteristics of ocean currents
1. The general movement of the currents in
the northern hemisphere is clockwise and in the
southern hemisphere, anti-clockwise (Fig. 3.7).
This is due to the Coriolis force which is a
deflective force.
2. The warm currents move towards the cold
seas and cool currents towards the warm seas.
13
14. Cont.
3. In the lower latitudes, the warm currents
flow on the eastern shores and cold on the
western shores. The situation is reversed in the
higher latitudes—the warm currents move
along the western shores and the cold currents
along the eastern shores.
4. Convergence along which the warm and
cold currents meet and divergence from which
they move out in different directions also
control the currents. 14
15. Cont.
5. The shape and position of coasts play an
important role in guiding the direction of
currents.
6. The currents flow not only at the surface but
also below the sea surface. Such currents are
caused by the differences in salinity and
temperature. For instance, heavy surface water
of the Mediterranean Sea sinks and flows
westward past Gibraltar as a sub-surface
current. 15
16. Types of ocean currents
There are different types of ocean currents on
different basis :
• Surface currents and Deep currents
• Upwelling currents and Downwelling currents
• Boundary currents
16
17. Surface and Deep currents
There are two types of currents, based on the
location i.e. where water will move.
17
Surface
currents
Deep
currents
18. Cont.
1. Surface currents : They are currents that
occur on the top layer of the ocean and
are primarily driven by wind. They affect
the water on the upper 300m of the
ocean. The currents, therefore, form
rotating systems in the middle of the
ocean systems, called gyres. Surface
currents are responsible for redistributing
heat of the sun.
18
19. Cont.
2. Deep-water Currents : These currents occur
deep inside the ocean. As they occur far below
the surface, they are not influenced by the
wind.
However, they arise as a result of variation in
the density of the ocean water and are
controlled by the temperature and salt content
of the water.
19
20. Surface Vs Deep currents
20
Sr. No. Surface currents Deep currents
1. Water movement upto
500m depth from surface
Water movement occur
below 500m depth
2. Velocity is higher Velocity is lower
3. Also called surface
circulation
Also called thermohaline
circulation
4. Wind driven Density driven (due to
differences in temperature
and salinity)
5. Primarily horizontal
motion
Both vertical and
horizontal motion
6. Occupy 10% of ocean
water
Occupy 90% of ocean
water
21. Vertical currents
Based on vertical movement of water , ocean
currents are of two types :
21
Upwelling
Currents
Downwelling
Currents
22. Cont.
1. Upwelling currents :
• These are the currents that move from
deep in the ocean heading towards the
surface.
• They are responsible for bringing organic
matter from below the ocean towards its
surface.
• For instance, they sweep nutrients
upwards, helping some marine life.
22
23. Cont.
• It can be seen when there are tremors or
earthquakes on the surface below the ocean
and the waves are pushed upwards.
• In Antarctica, upwelling currents pump
nitrogen and phosphates up from the deep
sea to blooms of algae and other plants.
23
24. Cont.
2. Downwelling currents :
These are currents that move material
from the surface of the ocean towards its
floor.
• Surface water can be forced downwards
by the pressure of the wind when currents
converge or wind drives the ocean against
a coastline
24
25. Upwelling Vs Downwelling
currents
25
Sr. No. Upwelling currents Downwelling currents
1. Movement of deep water
to surface
Movement of surface
water to deeper region
2. Carries nutrient rich water Carries deficient water
3. Water is colder Water is less cold
26. Boundary currents
Definition : Boundary currents are ocean
currents with dynamics determined by the
presence of a coastline.
Boundary currents are of two types :
26
Western Boundary
currents
Eastern Boundary
currents
27. Western Boundary currents
• Surface currents located on the western side
of the subtropical gyres, are called western
boundary currents.
• These are faster than their eastern
counterparts. In fact, they are among the
fastest surface currents in the ocean.
• One reason for the westward intensification
of boundary currents has to do with the
strengthening of the Coriolis effect with
latitude.
27
28. Cont.
• The Coriolis effect is stronger in the latitudes
of the westerlies than in the latitudes of the
trade winds.
• Waters moving in the western boundary
currents adjacent to the major gyres (North
and South Pacific and Atlantic basins and the
Indian basin) transport large quantities of
heat poleward from the tropics
28
29. Cont.
• Waters in western boundary currents
typically move 40 to 120 km (25 and 75 mi)
per day.
• These currents also extend much deeper than
most other surface currents, down to a depth
of 1000 m (3300 ft) or more.
29
30. Cont.
Major Western Boundary currents in the world
are :
• Gulf stream
• Kuroshio
• Labrador current
• Oyashio
• Brazil current
• East Australia current
• Agulhas current etc.
30
31. Eastern Boundary currents
• These are the surface currents that move
along the eastern edge of the ocean basin.
• Eastern boundary currents are relatively
shallow, broad and slow-flowing. They are
found on the eastern side of oceanic basins
(adjacent to the western coasts of
continents).
• These flow from high latitudes to the
equator.
• these currents transport colder waters into
the tropics, at about 3 to 7 kilometers per
31
32. Cont.
Major Eastern Boundary currents in the world
are :
• California current
• Canary current
• Peru current
• Benguela current etc.
32
33. Western Vs Eastern currents
33
Sr.No. Western Boundary
currents
Eastern Boundary
currents
1. Move along western
boundary of ocean basin
or eastern boundary of
continents
Move along eastern
boundary of ocean basin
or western boundary of
continents
2. Faster , narrow and
deeper
Slower , broad and
shallower
3. Move warm water from
equator towards the poles
Move cold water from
poles towards the equator
4. These waters have high
salinity and low oxygen
content
These waters have low
salinity and high oxygen
content
5. Have poor nutrient due to
infrequent upwelling
Nutrient rich due to
frequent upwelling
6. Low biomass High biomass
7. Stronger currents Weaker currents
