Ocean currents are large-scale circulation patterns in the ocean driven by factors like winds, solar heating, and water density differences from temperature and salinity changes. Major current systems include subtropical gyres in each ocean basin characterized by warm equatorial currents, western boundary currents, and eastern return flows. The Antarctic Circumpolar Current is a continuous current that circles Antarctica. Thermohaline circulation involves deep water formation and global overturning. Surface currents redistribute heat globally while deep currents transport nutrients and oxygen. Currents influence climate, marine life distributions, and biogeochemical cycles.

1. Geronimo R. Rosario

3.  Circulation- water movement in the ocean
 Currents- cohesive streams of sea water that circulate
through the oceans.
 Currents are also water masses in motion.
◦ Water Mass- a body of water identifiable from its
temperature, salinity or chemical content.
 Upper water mass- includes the well-mixed surface
layers of the ocean and the thermocline.
 Deep water mass- includes the water below the
thermocline to the bottom of the ocean.

4.  The ocean is forced from the surface by fluxes of
momentum and buoyancy (heat and freshwater).
 Surface currents are influenced by major wind belts
 Currents redistribute global heat.
 Most of the stratification is in the top km or so
 Thermohaline circulation affects deep currents.
 The sluggish thermohaline circulation forces ocean
overturning reaching in some regions to the sea floor,
resulting in the formation of the major water masses of
the global ocean:
 North Atlantic Deep Water (NADW)
 Antarctic Bottom Water (ABW).
 Currents affect marine life.

5.  Surface currents
◦ Surface circulation
◦ Wind-driven
◦ Warm and cold current
◦ Faster movement
◦ Primarily horizontal motion
◦ 10% of the total ocean water
 Deep currents
◦ Thermohaline circulation
◦ Driven by differences in density caused by differences in
temperature and salinity
◦ Sluggish movement
◦ Cold current
◦ Vertical and horizontal motions
◦ 90% of the total ocean water

6.  Surface ocean currents
◦ Transfer heat from warmer to cooler areas
◦ Similar to pattern of major wind belts
◦ Affect coastal climates
 Deep ocean currents
◦ Provide oxygen to deep sea

7. Ocean currents are driven by the following:
 1. Solar Heating
 2. Winds
 3. Gravity
 4. Coriolis
Effects of Ocean currents
 1. transfer heat from tropical to polar regions
 2. influence weather and climate
 3. distribute nutrients and scatter organisms

8.  Distribution of solar
heating is not uniform.
 The equator receives
more heat than the
polar regions.
 Solar heating causes
water to expand and
move

9.  Wind is caused by
pressure gradient force.
 Pressure gradient force
results in a net force
that is directed
from high to low
pressure
 The variation of
pressure is caused by
differential solar
heating.
 Coriolis force modify the
movements of the wind
creating the global wind
belts.
 Surface currents are
wind-driven circulation.

10.  pull water downhill
or pile against the
pressure gradient
(high/low)
 Causes
geostrophic
current together
with Coriolis force
 influences tides

11.  Caused by Earth’s
rotation, faster at
equator than at the
poles
 Changes the intended
path of all moving
bodies (winds and
currents).
 Motions are deflected
to the right in northern
hemisphere and left in
southern hemisphere
 Causes the gyres and
wind belts

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 Direct methods
◦ Floating
device tracked through
time
◦ Fixed current meter
 Indirect methods
◦ Pressure gradients
◦ Radar altimeters
◦ Doppler flow meter

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 Floating devices tracked through time
 Chemical tracers
◦ Tritium
◦ Chlorofluorocarbons
 Characteristic temperature and salinity
 Argo

14.  Global array of free-drifting
profiling floats that will measure
the temperature and salinity of
the upper 2000 m of the ocean in
or near real-time.

15.  Occur above pycnocline
 Frictional drag between wind and ocean
 Generally follow wind belt pattern
 Other factors:
◦ Distribution of continents
◦ Gravity
◦ Friction
◦ Coriolis effect

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 Large, circular loops
of moving water
 Bounded by:
◦ Equatorial current
◦ Western Boundary
currents
◦ Northern or Southern
Boundary currents
◦ Eastern Boundary
currents
 Centered around
30 degrees latitude N
and S

17.  North Atlantic – Columbus Gyre
 South Atlantic – Navigator Gyre
 North Pacific – Turtle Gyre
 South Pacific – Heyerdahl Gyre
 Indian Ocean – Majid Gyre

19. Four main currents flowing into one another:
 Equatorial Currents
◦ North or south
◦ Travel westward along equator
 Western Boundary Currents – warm waters
 Northern or Southern Boundary Currents – easterly
water flow across ocean basin
 Eastern Boundary Currents – cool waters

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 Equatorial Countercurrents – eastward flow between North and
South Equatorial Currents
 Subpolar Gyres
◦ Rotate opposite subtropical gyres
◦ Smaller and fewer than subtropical gyres
Subpolar currents
North Atlantic North Pacific
North Atlantic current Alaska current
Norwegian current Aleutian current
Labrador current Oyashio current
East Greenland current
Southern ocean Antarctic Circumpolar current

22. The westward flow of equatorial surface
wind produces anticyclonic current gyres.
1
2
3
4 5 4
3
They start with North Equatorial and South
Equa-torial currents, in the Atlantic (1, 2),
Pacific (3, 4) and Indian (only 5) oceans.
Warm
Cold
1 North Equatorial Current in the Atlantic Ocean
2 South Equatorial Current in the Atlantic Ocean
3 North Equatorial Current in the Pacific Ocean
4 South Equatorial Current in the Pacific Ocean
5 South Equatorial Current in the Indian Ocean

23. The westward flow of equatorial surface
wind produces anticyclonic current gyres.
1
2
3
4 5 4
3
Warm
Cold
6 Kuroshio or Japan Current
7 East Australian Current
8 Gulf Stream
9 Brazil Current
10 Agulhas Current
Blocked by land, these currents turn
polewards.
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7
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24. The westward flow of equatorial surface
wind produces anticyclonic current gyres .
Warm
Cold
11 California Current
12 Peru Current
13 Canary Current
14 Benguela Current
15 West Auatralian Current
They cool down as they reach ~45°, and
return as cold water currents
1
2
3
4 5 4
3
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13
15

25. Earth’s rotation produces the Circum-
Antarctic or Circum-Polar Current.
Warm
Cold
Also called the West Wind Drift, this cold
water current is the only ocean surface
current that joins the waters of all the
oceans.
1
2
3
4 5 4
3
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13
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Circum-Antarctic Circulation

26. Warm
Cold
Equatorial Counter Current is the gravity driven roll-
back of warm waters stacked on western margins
of the tropical ocean by westward flowing
equatorial surface wind.
1
2
3
4 5 4
3
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Circum-Antarctic Circulation
ECC ECC ECC
ECC can trigger El Niño

27.  Things to consider:
 1. Ekman spiral and transport
 2. Convergence and Divergence
 3. Vorticity
 4. Geostrophic balance

28.  The spiraling pattern
described by changes in
water direction and
speed with depth.
 Surface currents move at
an angle to the wind.
 The result is a surface flow
at 45o to the right in NH.
 Direction varies and
velocity decreases with
depth until 100m.
 Depth of frictional
influence- depth at which
motion ceases.
Factors:
1.Wind Pushes Water through
Wind Stress
2. Coriolis effect pushes water
to right(left)

29.  the net transport of water
by wind-induced motion.
 the overall water movement
due to Ekman spiral
 Ideal transport is 90º from
the wind
 Transport direction depends
on the hemisphere
 Ekman transport is
proportional to the speed of
the wind. Higher wind,
higher transport!

30.  Where water converge,
water piles up and
causes downwelling.
 Where water diverge,
water level lowers and
causes upwelling

31.  Surface seawater
moves towards an
area
 Surface seawater
piles up
 Seawater moves
downward
 Downwelling
 Low biological
productivity

32.  Surface
seawater moves
away
 Deeper seawater
(cooler, nutrient-
rich) replaces
surface water
 Upwelling
 High biological
productivity

33.  Upwelling – Vertical movement of cold, nutrient-
rich water to surface
◦ High biological productivity
 Downwelling – Vertical movement of surface
water downward in water column
◦ Low biological productivity

35. Peru

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 Ekman transport
moves surface
seawater
offshore.
 Cool, nutrient-
rich deep water
comes
up to replace
displaced surface
waters.

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 Offshore winds
 Seafloor obstruction
 Coastal geometry
change

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 Ekman transport
moves surface
seawater toward
shore.
 Water piles up,
moves downward in
water column
 Lack of marine life

39.  Langmuir circulation is a complex horizontal
helical (spiral) motion that extends parallel to the
wind.
Adjacent helices
rotate in opposite
directions creating
alternating zones of
convergence and
divergence.
Material floating on
the surface becomes
concentrated in the
zones of convergence
and form sea stripes
which parallel the
wind direction.

41.  Circulation and vorticity are the two primary
measures of rotation in a fluid.
 Circulation, which is a scalar integral quantity, is a
macroscopic measure of rotation for a finite area of
the fluid the fluid.
 Vorticity, however, is a vector field that gives a
microscopic measure of the rotation at any point in the
fluid.
 Vorticity is the tendency for elements of the fluid to
"spin.
 Vorticity can be related to the amount of “circulation”
or "rotation" (or more strictly, the local angular rate of
rotation) in a fluid.

42.  Absolute vorticity - vorticity as viewed in an inertial
reference frame.
 Relative vorticity -vorticity as viewed in the rotating
reference frame of the Earth.
 Planetary vorticity - vorticity associated with the
rotation of the Earth.
 When we talked about Coriolis we introduced the idea
of Planetary Vorticity.
 Every object on earth has a vorticity given to it by the
rotation of the earth (except an object on the equator).
This vorticity is dependent on latitude.

43.  Most large currents are
in Geostrophic balance.
 All currents are pushed
to the right(left).
 This piles water up on
the right(left).
 This creates a pressure
force back towards the
current.
 Eventually a balance is
reached. Pressure
BALANCES Coriolis!
current
Coriolis pushes water to
right(left). Piles up water.
Sealevel
Pressure force
current
coriolispressure

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 Geostrophic flow
(current) – a current
that develops out of the
Earth’s rotation and is
the result of a near
balance between
gravitational force and
the Coriolis effect.
 Ideal geostrophic
flow
 Friction generates
actual geostrophic
flow

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 Antarctic
Circumpolar Current
◦ Also called West
Wind Drift and
Penguin Gyre
◦ Only current to
completely encircle
Earth
◦ Moves more water
than any other
current

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 Antarctic Convergence
◦ Cold, dense Antarctic waters converge with
warmer, less dense sub-Antarctic waters
◦ Northernmost boundary of Antarctic Ocean
 East Wind Drift
◦ Polar Easterlies
◦ Creates surface divergence with opposite flowing
Antarctic Circumpolar Current
 Antarctic Divergence
◦ Abundant marine life

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 North Atlantic
Subtropical Gyre
◦ North Equatorial
Current
◦ Gulf Stream
◦ North Atlantic Current
◦ Canary Current
◦ South Equatorial
Current
◦ Atlantic Equatorial
Counter Current

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 South Atlantic
Subtropical Gyre
◦ Brazil Current
◦ Antarctic Circumpolar
Current
◦ Benguela Current
◦ South Equatorial
Current

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 Best studied of all
ocean currents
 Meanders and loops
 Merges with
Sargasso Sea
◦ Circulates around
center of North
Atlantic Gyre
◦ Unique biology –
Sargassum

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 Meanders or loops may
cause loss of water
volume and generate:
◦ Warm-core rings –
warmer Sargasso Sea
water trapped in loop
surrounded by cool water
◦ Cold-core rings – cold
water trapped in loop
surrounded by warmer
water
 Unique biological
populations

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 Labrador Current
 Irminger Current
 Norwegian
Current
 North Atlantic
Current

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North-moving currents – warm
 Gulf Stream warms East coast of United States
and northern Europe
 North Atlantic and Norwegian Currents warm
northwestern Europe
South-moving currents – cool
 Labrador Current cools eastern Canada
 Canary Current cools north African coast

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 Monsoons – seasonal reversal of winds over
northern Indian Ocean
 Heat Capacity Differential
 Northeast monsoon – winter
 Southwest monsoon – summer

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55.  Affects
seasonal
land weather
 Affects
seasonal
Indian Ocean
current
circulation
 Affects
phytoplankton
productivity

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 Indian Ocean
Subtropical
Gyre
◦ Agulhas Current
◦ Australian
Current
◦ Leeuwin Current

57.  North Pacific
Subtropical Gyre
◦ Kuroshio
◦ North Pacific Current
◦ California Current
◦ North Equatorial Current
◦ Alaskan Current

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 South Pacific
Subtropical Gyre
◦ East Australian Current
◦ Antarctic Circumpolar
Current
◦ Peru Current
◦ South Equatorial Current
◦ Equatorial Counter
Current

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60.  Both are shallow(thin layers
of fluid)
 Both are rotating rapidly
 Both are stratified fluids
(usually stably, with lighter
fluid on top)
 The ocean has sidewall
boundaries.
 The ocean has a definitive
top while the atmosphere
does not.
 The ocean is almost
incompressible.

61.  The atmosphere is driven
primarily by thermal forcing at its
lower boundary; the oceans are
driven primarily mechanically
driven from the top.
 The atmosphere has significant
internal diabatic heating (latent
heat release; radiation); the
oceans do not.
 The oceans are salty, the
atmosphere is moist and cloudy
 The ocean is dense (~1000 times
air), with a large heat capacity
and large inertia. 2.5m of water
holds as much heat as the whole
depth of the atmosphere

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 Walker Circulation Cell – normal conditions
◦ Air pressure across equatorial Pacific is higher in eastern
Pacific
◦ Strong southeast trade winds
◦ Pacific warm pool on western side of ocean
◦ Thermocline deeper on western side
◦ Upwelling off the coast of Peru

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64.  El Niño (Spanish for “the Child” in reference to baby
Jesus) = warm surface current in equatorial eastern
Pacific that occurs periodically around Christmastime
 Southern Oscillation = change in atmospheric
pressure over Pacific Ocean accompanying El Niño
 ENSO describes a combined oceanic-atmospheric
disturbance
 La Niña is a climate pattern that describes the cooling
of surface ocean waters along the tropical west coast
of South America.
 La Nina is considered to be the counterpart to El Nino,
which is characterized by unusually warm ocean
temperatures in the equatorial region of the Pacific
Ocean.

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Walker Cell Circulation disrupted
 High pressure in eastern Pacific weakens
 Weaker trade winds
 Warm pool migrates eastward
 Thermocline deeper in eastern Pacific
 Downwelling
 Lower biological productivity
◦ Peruvian fishing suffers

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 Increased pressure difference across equatorial
Pacific
 Stronger trade winds
 Stronger upwelling in eastern Pacific
 Shallower thermocline
 Cooler than normal seawater
 Higher biological productivity

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 El Niño warm phase about every
2–10 years
 Highly irregular
 Phases usually last 12–18 months
 10,000-year sediment record of events
 ENSO may be part of Pacific Decadal Oscillation
(PDO)
◦ Long-term natural climate cycle
◦ Lasts 20–30 years

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 1982 – 1983
 1997 – 1998
 Flooding,
drought,
erosion, fires,
tropical storms,
harmful effects
on marine life
 Unpredictable

73.  Tropical Ocean−Global Atmosphere (TOGA)
program
◦ 1985
◦ Monitors equatorial South Pacific
◦ System of buoys
 Tropical Atmosphere and Ocean (TOA) project
◦ Continues monitoring
 ENSO still not fully understood

74.  The ocean is divided into three zones:
 Surface zone - the upper layer of the ocean,
containing the least dense water. The surface
zone is only about 2% of total ocean volume.
 Pycnocline - a zone in which density increases
with depth, containing about 18% of all ocean
water.
 Deep zone – contains about 80% of all ocean
water. There is little change in density throughout
this layer.

76.  Conditions of the deep ocean:
◦ Cold
◦ Still
◦ Dark
◦ Essentially no productivity
◦ Sparse life
◦ Extremely high pressure

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 Thermohaline Circulation – deep ocean
circulation driven by temperature and density
differences in water
 Below the pycnocline
 90% of all ocean water
 Slow velocity

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 Originates in high latitude surface ocean
 Cooled, now dense surface water sinks and
changes little.
 Deep-water masses identified on temperature–
salinity (T–S) diagram
◦ Identifies deep water masses based on temperature,
salinity, and resulting density

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 Some deep-water masses
◦ Antarctic Bottom Water
◦ North Atlantic Deep Water
◦ Antarctic Intermediate Water
◦ Oceanic Common Water
 Cold surface seawater sinks at polar
regions and moves equatorward

82.  A current that connects
the Ocean’s Surface
Waters to Deep waters
via Upwelling and
Downwelling
 Also called
Thermohaline
Circulation
 Mixes waters within and
throughout all oceans
Oxygen flows down
Nutrients flow up

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 Currents carry
more energy
than winds
 Florida–Gulf
Stream Current
System
 Underwater
turbines
◦ Expensive
◦ Difficult to maintain
◦ Hazard to boating