ocean currents water masses

1. It all begins with the sun……

2. Resultant flow which gives rise to vertical
motion in and below the Ekman layer
-Upwelling
-Downwelling

3. Ekman pumping

4. © 2011 Pearson Education, Inc.
Geostrophic Flow
Ekman transport piles
up water within
subtropical gyres.
Surface water flows
downhill and to the
right.
Geostrophic flow –
balance of Coriolis Effect
and gravitational forces
Ideal geostrophic flow
Friction generates actual
geostrophic flow

5. Geostrophic flow and western
intensification
Geostrophic flow
causes a hill to form
in subtropical gyres
The center of the
gyre is shifted to the
west because of
Earth’s rotation
Western boundary
currents are
intensified Figure 7-7

6. 30o
30o
60o
60o
90o
90o
0o
Forces
1. Solar Heating
(temp, density)
2. Winds
3. Coriolis
Surface Currents

7. Factors Influencing Nature and Movement of Ocean
Currents:
1. Factors related to the earth’s rotation:
Gravitational force and force of deflection.
2. Factors originating within the sea:
Atmospheric pressure, winds, precipitation, evaporation
and insolation.
3. Factors originating within the sea:
Pressure gradient, temperature difference, salinity, density
and melting of ice.
4. Factors modifying the ocean currents:
Direction and shape of the coast, seasonal variations and
bottom topography.

8. Surface and Deep-Sea Current
Interactions
“Global Ocean Conveyor Belt”

9. Global ocean circulation that is driven by differences in the density of the
sea water which is controlled by temperature and salinity.

10. White sections represent warm surface currents.
Purple sections represent deep cold currents

14. Formation of Antarctic Bottom Water
(AABW)

15. Weddel Sea (Flichner ice shelf) and Ross Sea (Ross Ice
Shelf)
Weddel Sea – partially isolated embayment -greatest
contributor
There is less entrainment than with NADW so AABW is
densest water in ocean.

16. Cold wind blows ice offshore (polyna) allowing ice to
continually form.
During freezing, salts are left behind (brine formation)
resulting in water that is more saline.
Surface waters are chilled to temperature of ~ -1.9°C,
salinity is 34.6 psu.
 This cold dense water collects on the Antarctic shelf and
sinks to the bottom of the adjacent deep-ocean basin.
In the process of mixing, mixes with other waters and is
warmed.
Resulting water is ~ -0.4-1°C and 34.6 to 34.8 psu.

17. Formation of North Atlantic Bottom
Water (NABW)

18. © 2011 Pearson Education, Inc.
Antarctic CirculationAntarctic Circumpolar
Current
Also called West Wind
Drift and Penguin Gyre
Only current to
completely encircle
Earth
Moves more water than
any other current

19. © 2011 Pearson Education, Inc.
Antarctic CirculationAntarctic Circumpolar
Current
Also called West Wind
Drift and Penguin Gyre
Only current to
completely encircle
Earth
Moves more water than
any other current

20. © 2011 Pearson Education, Inc.
Antarctic Circulation
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

21. © 2011 Pearson Education, Inc.
Atlantic Ocean Circulation
Equatorial Atlantic circulation
At the Equator, Atlantic extends from 10° E to 45 °
W – 6000 km
Main currents
North equatorial counter current (NECC) flowing
to east from 8° -3° N
South Equatorial current (SEC) flowing west from
3°N to 8°S
Equatorial undercurrent (EUC) flowing east at
equator about 50-300m
Brazil coastal current

22. © 2011 Pearson Education, Inc.
Atlantic Ocean CirculationNorth Atlantic
Subtropical Gyre
Rotates clockwise –
Coriolis effect
Separated from
South Atlantic gyre
by Atlantic
equatorial counter
current

23. © 2011 Pearson Education, Inc.
Atlantic Ocean CirculationNorth Atlantic
Subtropical Gyre
North Equatorial
Current
Gulf Stream
North Atlantic Current
Canary Current
South Equatorial
Current
Atlantic Equatorial
Counter Current

24. © 2011 Pearson Education, Inc.
Atlantic Ocean CirculationSouth Atlantic
Subtropical Gyre
 Brazil Current
 Antarctic Circumpolar
Current
 Benguela Current
 South Equatorial
Current

25. South Atlantic – upper water gyre – extends from
surface to a depth of 200 m near the equator to 800m
southern limits of gyre at Subtropical convergence
Wind stress of South East trade winds between equator
and 10-15° S – main driving force
Acts on sea and forms South Equatorial current (SEC)
– greatest strength just below equator – flows west
towards American side of South Atlantic
Spills by topographic interference by eastern
prominence of Brazil. Part of SEC moves off
northeastern coast of South America towards
Caribbean and North Atlantic, rest is turns southwards
as brazil current

26. Brazil current coming from the tropics is warm and
saline, turns east and continues across Atlantic as
Antarctic Circumpolar current (WWD) and moves
eastward. The Brazil current is much smaller than the
Northern Hemisphere counterpart i.e. the Gulf stream
due to the splitting of SEC
WWD than turns north up on African side as the
Benguela Current which flows equatorward along
Africa’s western coast
Benguela current is slow drifting cold current because
of the contribution of Subantartic water and of
upwelling along the African coast
Falkland current

27. Falkland current – is outside the South Atlantic gyre,
but is a significant north bound flow of cold water.
Current flows from Drake passage and moves along
the western margin of South Atlantic up the coast of
South America. Falkland current impart cold current
that moves along the coast of Argentina as far as
north as 30°S thus separating Brazil current from
coast at this point.
South Atlantic circulation is bounded on south by
Subtropical Convergence.

28. © 2011 Pearson Education, Inc.
Gulf Stream
 Best studied of all ocean currents
 Meanders and loops
 Merges with Sargasso Sea
 Circulates around center of North Atlantic Gyre
 Unique biology – Sargassum

29. © 2011 Pearson Education, Inc.
Gulf Stream 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

30. © 2011 Pearson Education, Inc.
Other North Atlantic Currents
Labrador Current
Irminger Current
Norwegian Current
North Atlantic Current

31. © 2011 Pearson Education, Inc.
Climate Effects of North Atlantic
Currents
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

32. © 2011 Pearson Education, Inc.
Indian Ocean Circulation
Monsoons – seasonal reversal of winds over northern
Indian Ocean
Heat Capacity Differential
Northeast monsoon – winter
Southwest monsoon – summer

33. © 2011 Pearson Education, Inc.
Indian Ocean Circulation

34. © 2011 Pearson Education, Inc.
Indian Ocean Monsoon
Affects
seasonal
land weather
Affects
seasonal
Indian Ocean
current
circulation
Affects
phytoplankton
productivity

35. © 2011 Pearson Education, Inc.
Indian Ocean Circulation
Indian Ocean Subtropical Gyre
Agulhas Current
Australian Current
Leeuwin Current

36. © 2011 Pearson Education, Inc.
Pacific Ocean Circulation
North Pacific Subtropical Gyre
Kuroshio
North Pacific Current
California Current
North Equatorial Current
Alaskan Current

37. © 2011 Pearson Education, Inc.
Pacific Ocean Circulation
South Pacific Subtropical Gyre
East Australian Current
Antarctic Circumpolar Current
Peru Current
South Equatorial Current
Equatorial Counter Current

38. © 2011 Pearson Education, Inc.
Pacific Ocean Circulation

39. Upwelling and downwelling
Vertical movement of water
Upwelling = movement of deep water to surface
 Hoists cold, nutrient-rich water to surface
 Produces high productivities and abundant marine life
Downwelling = movement of surface water down
 Moves warm, nutrient-depleted surface water down
 Not associated with high productivities or abundant
marine life

40. upwelling
downwelling

41. Upwelling
Causes cold, nutrient rich water from the deep ocean to
rise to the surface.

42. El Nino and La Nina
El Nino is a change in water temperature in the
Pacific ocean that produces a warm current.
La Nina is a change in temperature in the Eastern
Pacific that causes surface water temperature to
be much colder than usual

43. BOTH El nino and La Nina can cause flooding (too
much rain) and drought (too little rain) in different
places on Earth. Upwelling does not occur where it
normally would and this affects fish and sealife.

44. El Niño-Southern Oscillation
(ENSO)
El Niño = warm surface current in equatorial eastern
Pacific that occurs periodically around December
Southern Oscillation = change in atmospheric
pressure over Pacific Ocean accompanying El Niño
ENSO describes a combined oceanic-atmospheric
disturbance

45. • Oceanic and atmospheric
phenomenon in the Pacific Ocean
• Occurs during December
• 2 to 7 year cycle
Sea Surface Temperature
Atmospheric Winds
Upwelling

49. El NiñoNon El Niño
1997

50. Non El Niño
El Niño
Thermocline –
layer of ocean right beneath the
“mixed layer” where temperatures
decrease rapidly.
upwelling

51. El Niño events over the last 55 years
El Niño warmings (red) and La Niña coolings (blue) since 1950. Source:
NOAA Climate Diagnostics Center

52. El Nino Animation
World Wide Effects of El Niño
• Weather patterns
• Marine Life
• Economic resources

53. Effects of severe El Niños

54. Coriolis Effect
Because of the coriolis effect, winds appear to deflected
to the east or west depending on the direction winds
are traveling.

55. A buoy records data about surface ocean temperature
and transmits (sends) the information to a satellite in
space that then transmits(sends) the information to
scientists.

56. Land breeze and sea breeze

57. Water has a much higher heat capacity (absorbs and lets go
of heat more) slowly than land, water temperature will
increase and decrease less than land temperature.
e.g. during daytime, land temperatures might change by
tens of degrees,
water temperature change by less than half a degree.

58. i.e. coastal land temperatures don’t fluctuate (go up and
down) extremely (a lot) because the ocean water nearby
doesn’t fluctuate much.

59. © 2011 Pearson Education, Inc.
Chapter Overview
Ocean currents are moving loops of water.
Surface currents are influenced by major
wind belts.
Currents redistribute global heat.
Thermohaline circulation affects deep currents.
Currents affect marine life.

60. © 2011 Pearson Education, Inc.
Types of Ocean Currents
Surface currents
Wind-driven
Primarily horizontal motion
Deep currents
Driven by differences in density caused
by differences in temperature and salinity
Vertical and horizontal motions

61. © 2011 Pearson Education, Inc.
Measuring Surface CurrentsDirect methods
Floating
device tracked through
time
Fixed current meter
Indirect methods
Pressure gradients
Radar altimeters
Doppler flow meter

62. © 2011 Pearson Education, Inc.
Global Surface Current Flow

63. © 2011 Pearson Education, Inc.
Measuring Deep Currents
Floating devices tracked through time
Chemical tracers
Tritium
Chlorofluorocarbons
Characteristic temperature and
salinity
Argo

64. © 2011 Pearson Education, Inc.
Argo

65. © 2011 Pearson Education, Inc.
Surface CurrentsOccur above pycnocline
Frictional drag between wind and ocean
Generally follow wind belt pattern
Other factors:
Distribution of continents
Gravity
Friction
Coriolis effect

66. © 2011 Pearson Education, Inc.
Subtropical Gyres
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

67. © 2011 Pearson Education, Inc.
Five Subtropical Gyres
North Atlantic – Columbus Gyre
South Atlantic – Navigator Gyre
North Pacific – Turtle Gyre
South Pacific – Heyerdahl Gyre
Indian Ocean – Majid Gyre

68. © 2011 Pearson Education, Inc.
Subtropical Gyres and Currents

69. © 2011 Pearson Education, Inc.
Subtropical Gyre CurrentsFour 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

70. © 2011 Pearson Education, Inc.
Gyres and Boundary Currents

71. © 2011 Pearson Education, Inc.
Other Surface Currents
Equatorial Countercurrents – eastward flow between
North and South Equatorial Currents
Subpolar Gyres
Rotate opposite subtropical gyres
Smaller and fewer than subtropical gyres

72. © 2011 Pearson Education, Inc.
Western Intensification
Top of hill of water displaced toward west due
to Earth’s rotation
Western boundary currents intensified in
both hemispheres
Faster
Narrower
Deeper
Warm
Coriolis Effect contributes to western
intensification

73. © 2011 Pearson Education, Inc.
Eastern Boundary Currents
Eastern side of ocean basins
Tend to have the opposite properties of Western
Boundary Currents
Cold
Slow
Shallow
Wide

74. © 2011 Pearson Education, Inc.
Eastern and Western Boundary
Currents

75. © 2011 Pearson Education, Inc.
Ocean Currents and ClimateWarm ocean currents warm the air at
the coast.
Warm, humid air
Humid climate on adjoining landmass
Cool ocean currents cool the air at the
coast.
Cool, dry air
Dry climate on adjoining landmass

76. © 2011 Pearson Education, Inc.
Ocean Currents and Climate

77. © 2011 Pearson Education, Inc.
Upwelling and Downwelling
Upwelling – Vertical movement of cold, nutrient-rich
water to surface
High biological productivity
Downwelling – Vertical movement of surface water
downward in water column

78. © 2011 Pearson Education, Inc.
Diverging Surface WaterSurface waters move
away from area
Equatorial upwelling
Coastal upwelling

79. © 2011 Pearson Education, Inc.
Coastal UpwellingEkman transport
moves surface
seawater offshore.
Cool, nutrient-rich
deep water comes
up to replace displaced
surface waters.
Example: U.S.
West Coast

80. © 2011 Pearson Education, Inc.
Other Types of UpwellingOffshore winds
Seafloor obstruction
Coastal geometry
change

81. © 2011 Pearson Education, Inc.
Converging Surface WaterSurface waters move
toward each other.
Water piles up.
Low biological
productivity

82. © 2011 Pearson Education, Inc.
Coastal DownwellingEkman transport
moves surface
seawater toward shore.
Water piles up, moves
downward in water
column
Lack of marine life

84. © 2011 Pearson Education, Inc.
Atmospheric-Ocean Connections in the
Pacific Ocean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

85. © 2011 Pearson Education, Inc.
Normal Conditions, Walker Circulation

86. © 2011 Pearson Education, Inc.
El Niño – Southern Oscillation (ENSO)
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

87. © 2011 Pearson Education, Inc.
ENSO Conditions in the Pacific Ocean

88. © 2011 Pearson Education, Inc.
La Niña – ENSO Cool Phase
Increased pressure difference across equatorial Pacific
Stronger trade winds
Stronger upwelling in eastern Pacific
Shallower thermocline
Cooler than normal seawater
Higher biological productivity

89. © 2011 Pearson Education, Inc.
La Niña Conditions

90. © 2011 Pearson Education, Inc.
Occurrence of ENSO Events
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

91. © 2011 Pearson Education, Inc.
ENSO Occurrences

92. © 2011 Pearson Education, Inc.
ENSO has Global Impacts

93. © 2011 Pearson Education, Inc.
Notable ENSO Events1982 – 1983
1997 – 1998
Flooding,
drought,
erosion, fires,
tropical storms,
harmful effects
on marine life
Unpredictable

94. © 2011 Pearson Education, Inc.
Predicting El Niño Events
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

95. © 2011 Pearson Education, Inc.
Deep-Ocean Currents
Thermohaline Circulation – deep ocean circulation
driven by temperature and density differences in
water
Below the pycnocline
90% of all ocean water
Slow velocity

96. © 2011 Pearson Education, Inc.
Thermohaline Circulation
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

97. © 2011 Pearson Education, Inc.
Thermohaline Circulation

98. © 2011 Pearson Education, Inc.
T–S Diagram

99. © 2011 Pearson Education, Inc.
Thermohaline Circulation
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

100. © 2011 Pearson Education, Inc.
Conveyor Belt Circulation

101. © 2011 Pearson Education, Inc.
Power From Currents
Currents carry
more energy
than winds
Florida–Gulf
Stream Current System
Underwater
turbines
Expensive
Difficult to maintain
Hazard to boating

102. Measuring surface currents
Direct methods
Float meters
 Intentional
 Inadvertent
Propeller meters
Indirect methods
Pressure gradients
Satellites
Doppler flow meters Figure 7B

103. Surface currents closely follow
global wind belt pattern
Trade winds at 0-30º
blow surface currents to
the east
Prevailing westerlies at
30-60º blow currents to
the west
Figure 7-3

104. Figure 7-4

105. Current gyres
Gyres are large circular-moving loops of
water
Subtropical gyres
 Five main gyres (one in each ocean basin):
 North Pacific
 South Pacific
 North Atlantic
 South Atlantic
 Indian
 Generally 4 currents in each gyre
 Centered at about 30º north or south latitude

106. Current gyres
Gyres (continued)
Subpolar gyres
 Smaller and fewer than subtropical gyres
 Generally 2 currents in each gyre
 Centered at about 60º north or south latitude
 Rotate in the opposite direction of adjoining subtropical
gyres

107. Western intensification of
subtropical gyres
The western boundary currents of all subtropical
gyres are:
Fast
Narrow
Deep
Western boundary currents are also warm
Eastern boundary currents of subtropical gyres have
opposite characteristics

108. Currents and climate
Warm current warms
air high water vapor
humid coastal climate
Cool current cools air
low water vapor dry
coastal climate
Figure 7-8a

109. Upwelling and downwelling
Vertical movement of water ( )
Upwelling = movement of deep water to surface
 Hoists cold, nutrient-rich water to surface
 Produces high productivities and abundant marine life
Downwelling = movement of surface water down
 Moves warm, nutrient-depleted surface water down
 Not associated with high productivities or abundant
marine life

110. Coastal upwelling and
downwelling
Ekman transport moves surface water away from
shore, producing upwelling
Ekman transport moves surface water towards shore,
producing downwelling
Figure 7-11

111. Other types of upwelling
Equatorial upwelling
Offshore wind
Sea floor obstruction
Sharp bend in coastal
geometry
Figure 7-9
Equatorial upwelling

112. Figure 7-13

113. Figure 7-14

114. Figure 7-15

115. The Gulf Stream and sea
surface temperatures
The Gulf Stream is a
warm, western
intensified current
Meanders as it moves
into the North Atlantic
Creates warm and cold
core rings
Figure 7-16

116. Figure 7-17

117. El Niño-Southern Oscillation
(ENSO)
El Niño = 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

118. Figure 7-18a

119. Figure 7-18b

120. Figure 7-18c

121. The 1997-98 El Niño
Sea surface
temperature
anomaly map shows
warming during
severe 1997-98 El
Niño
Internet site for El
Niño visualizations
Current state of the
tropical Pacific
Figure 7-19a

122. El Niño recurrence interval
Typical recurrence interval for El Niños = 2-12
years
Pacific has alternated between El Niño and La
Niña events since 1950
Figure 7-20

123. Figure 7-21

124. Figure 7-23
Northeast monsoon Southwest monsoon

125. Deep currents
Deep currents:
Form in subpolar regions at the surface
Are created when high density surface water sinks
Factors affecting density of surface water:
 Temperature (most important factor)
 Salinity
Deep currents are also known as thermohaline
circulation

126. Deep ocean characteristics
Conditions of the deep ocean:
Cold
Still
Dark
Essentially no productivity
Sparse life
Extremely high pressure

127. Identification of deep currents
Deep currents are
identified by
measuring
temperature (T)
and salinity (S),
from which
density can be
determined
Figure 7-24

128. Figure 7-25

129. Figure 7-27