1. Oceanic Circulation Current = a moving mass of water
OCEAN WATER MOVES IN CURRENTS CAUSED BY WIND AND DIFFERENCE IN WATER DENSITY (beneath surface zone)

2. Oceanic Circulation Surface Currents
horizontally flowing water in the uppermost 400m of the ocean
10% of water in Oceans moves this way
driven by thermal expansion & contraction and WIND friction

3. Oceanic Circulation Surface Currents Thermohaline Circulation
horizontally flowing water in the uppermost 400m of the ocean
driven by thermal expansion & contraction and wind friction
Thermohaline Circulation
slower, deeper circulation

4. Oceanic Circulation Surface Currents Thermohaline Circulation
horizontally flowing water in the uppermost 400m of the ocean (above pycnocline)
driven by thermal expansion & contraction and wind friction
Thermohaline Circulation
slower, deeper circulation (below pycnocline)
due to the action of gravity on water masses of different densities

5. Refresher
From
Ch. 6

6. “Thermocline” (refresher)
Tropical and subtropical oceans are permanently layered with warm, less dense surface water separated from cold, dense deep water by a thermocline.
The thermocline is a layer in which water temperature and density change rapidly.
Temperate regions have a seasonal thermocline and polar regions have none.

7. Thermocline, Halocline, and Pycnocline

8. Surface Currents Solar heating
water expands at equator and contracts near poles

9. Surface Currents Solar heating
water expands at equator and contracts near poles
water moves toward poles due to gravity

10. Surface Currents Solar heating
water expands at equator and contracts near poles
water moves toward poles due to gravity
water lags behind earth’s rotation & piles up on west sides of oceans

11. Surface Currents Wind Friction drags water along Coriolis effect
primary force responsible for surface currents
Friction drags water along
Coriolis effect
The “piled up” water will move in direction the wind is blowing it UNTIL the coreolis determines final direction (right of wind direction in N. Hemisphere)

12. Surface Currents
Continents prevent continuos flow and deflect water…

13. Surface Currents Continents prevent continuous flow and deflect water…
Gyre
the circular flow around the periphery of an ocean basin

14. Trade Winds = Easterlies Winds are Driven by Uneven Solar Heating and
the earths
spin
Fig 8-1, g

15. Surface Winds, Sun’s heat, Coreolis Effect and Gravity = surface
current =
gyres
Fig 8-2, g

16. 5 major ocean gyres

17. Six great current circuits
North Atlantic Gyre
South Atlantic Gyre
North Pacific Gyre
South Pacific Gyre
West Wind drift or Antarctic Circumpolar Current

18. Sea Surface Temperatures
Insolation and ocean-surface water temperature vary with the season.
Ocean temperature is highest in the tropics (25oC) and decreases poleward.
Figure 5-9a Sea-Surface Temperature in August
Using Thermocline Principles

19. Northern
Atlantic
Gyre
Fig 8-3, g

20. Flow within Gyres Western Boundary Currents (ex: Gulf Stream)
narrow, fast, deep currents that carry warm water toward poles

21. Flow within Gyres Western Boundary Currents (ex: Gulf Stream)
narrow, fast, deep currents that carry warm water toward poles
westward intensification - more concentrated due to water piling up due to eastward rotation of earth

22. Fig 8-13b, g

23. Flow within Gyres Eastern Boundary Currents (ex: Canary Current)
broad, slow, shallow currents that carry cold water toward equator

25. Flow within Gyres
Transverse Currents (ex: North Atlantic Current, North Equatorial current)
currents that flow from east to west or west to east

26. Flow within Gyres Currents affect climate:
North Atlantic current warms England
California current cools San Francisco in the summer

27. Fig 8-8, g

28. Figure 8.9
The general surface circulation of the North Atlantic. The numbers indicate flow rates in sverdrups (1 sv = 1 million cubic meters of water per second).
Fig. 8-9, g

29. …Gyres…a final word Gyres consist of currents that blend into 1
Flow is continuous
Caused by combo of: wind energy, friction, the Coreolis effect and the pressure gradient

30. EKMAN SPIRAL Sum of water direction in (multi) layered Ocean
Net motion of water (down to 100 meters) w/ ekman spiral included = ekman transport
Each layer in “spiral” acts differently

31. Fig 8-5, g

32. 7
Fig 8-5a, g

33. Fig 8-5b, g

34. Fig 8-5c, g

36. fnft

37. Figure 15.32
fnft

39. Convergence & Divergence of Water Currents in the Northern Hemisphere

41. Eddy Formation
Western boundary of Gulf Stream has distinct Temperature, Speed and Direction
Meanders (EDDIES) form here
Eddies pinch off and become isolated cells of either warm or cold water

42. Eddy

43. Gulf stream
Viewed from
Space
1=east coast
off Fl.
2=warm eddy
3=cold eddy
4=mix of
surface
and
surrounding
waters

45. Wind- Induced Vertical Circulation
Upwelling
upward movement of water
Downwelling
downward movement of water

46. Fig 8-16, g

47. Principal regions of coastal upwelling and down-current areas of increased primary productivity

48. Wind- Induced Vertical Circulation
Coastal Upwelling
cold, deeper water upwells to replace the surface water
leads to increased nutrients & productivity and cooler climates

49. Coastal upwelling in the Northern Hemisphere

50. Wind- Induced Vertical Circulation
Equatorial Upwelling
westward flowing equatorial currents are deflected poleward
deeper water comes up to replace the surface water

52. Fig 8-14a, g

53. Wind- Induced Vertical Circulation
Downwelling
water driven toward the coast will be forced down
Brings down dissolved gases

54. Deep Circulation Thermohaline Circulation
Driven by density differences
water masses do not mix easily but flow above or beneath each other

55. Classic thermohaline circulation
Fnft

56. Cross-section of the South Atlantic Ocean

57. 5 Common Water Masses Surface water Central water Intermediate Water
to 200m
Central water
to bottom of thermocline
Intermediate Water
to 1500m
Deep water
below intermediate but not in contact with bottom
Bottom water
in contact with bottom

58. Some Water Masses in the Deep Atlantic
Antarctic Bottom Water
North Atlantic Deep water
Mediterranean Intermediate Water
Antarctic Intermediate Water

59. Water layers and deep circulation of Atlantic

61. The water sinks to a density-appropriate level and then slowly flows equatorward across the basin.
Deep water gradually mixes with other water masses and eventually rises to the surface.

62. Figure 8.20: The global pattern of deep circulation resembles a vast “conveyor belt” that carries surface water to the depths and back again. Begin with the formation of North Atlantic Deep Water north of Iceland. This water mass flows south through the Atlantic, then flows over (and mixes with) deep water formed near Antarctica. The combined mass circumnavigates Antarctica and then moves north into the Indian and Pacific Ocean basins. Diffuse upwelling in all of the ocean returns some of this water to the surface. Water in the conveyor gradually warms and mixes upward to be returned to the North Atlantic by surface circulation. The whole slow-moving system is important in transporting water and heat.
Fig. 8-23, p. 190

63. Figure 8.24
A simplified view of thermohaline circulation in the Atlantic. Surface water becomes dense and sinks in the north and south polar regions. Being denser, Antarctic Bottom Water slips beneath North Atlantic Deep Water. The water then gradually rises across a very large area in the tropical and temperate zones, then flows poleward to repeat the cycle. As noted in the text, fresh water arriving in the North Atlantic from rapidly melting polar ice could slow the formation of North Atlantic Deep Water with profound implications for the climate of Europe.
Fig. 8-24, g

64. Thermohaline Circulation
Sinking of water masses is offset by slow, gradual rising across warmer temperate and tropical zones

65. Thermohaline Circulation
Much slower than surface circulation
hundreds of years (1500?) vs 1 year (North Atlantic Gyre)

66. Remember…
From lecture #1 of the course – those 1st “facts” are extremely important
Let’s review…

67. Important Facts
81% of the Southern Hemisphere is covered by Ocean (remember that! It’ll become really important later…); while only 61% of the Northern Hemisphere is covered – WHY?
The Oceans are 4X as deep as the Continents are high (average depth = 2.5 miles).
The Pacific (Ocean) is so huge that it covers almost ½ of the Earth’s surface; it is also the Earth’s largest collection of water.
We have 100X more “aquatic” habitats available on earth than terrestrial habitats (1.4 billion cubic kilometers).

69. A synthetic view of our ocean planet
© digitalife/ShutterStock, Inc.

70. El Nino
(if time permits)

71. ENSO events
Surface winds generally move from East to West in Tropical (equator) Pacific but every 3-8 yrs. these pressure areas (typically high to low) change and you get a reversal of wind direction/atmospheric pressure (low to high) = southern oscillation
El nino = water flow name (+ southern osc. = ENSO event)
Still no one really knows why/how this occurs

72. El Nino
“Current of the Christ Child” because Peru had an (unexpected) abundance of fishing 1 X-Mas.

73. Why 2 names?
Southern oscillation (ENSO): Weather related name (pressure changes in wind patterns are clearly associated; these drive water change)
El Nino: oceanographic name (associated w/ water and temp. patterns that change biological species’ productivity in the Pacific)

74. Upwelling of cold water
A non el nino year
Thermocline rises
Upwelling of cold water
Fig 8-16a, g

75. What happens (non El Nino)?
Warmest part of the Worlds’ ocean = western Pacific b/c warm water moves East to West and builds up there
As a result you get a decreased thermocline (lower in water column, less upwelling)

76. Figure 8.21
Surface temperatures for southern California in January of the normal year of 1982 (left) and in the same month of an El Niño year (1983, right).
Fig. 8-21, g

77. Fig 8-16d, g

78. What happens (El Nino)?
Warm water (that usually moves East to West) shifts to West –> East movement
Slows trade winds (southern oscillation)
Pressure system shifts
Warm water on other side, less where expected
As a result you get an increased thermocline (higher in water column, more upwelling)

79. Figure 8.22
El Niño changes atmospheric circulation and weather patterns.
(a) During an El Niño, low atmospheric pressure south of Alaska allows storms to move unimpeded to the Pacific coast of North America. The resulting weather is wet and cool to the south, and warm and dry in the north.
Fig. 8-22a, g

80. Fig 8-16b, g

81. El nino year
Eastward
Movement of
Water, no
upwelling
Fig 8-16c, g

82. The opposite – La Nina “The Girl”
When we “return to normal,” it is fast w/ a huge change and increased currents, increased upwelling (thus increased cold water upwards) result.
Trade winds renewed

83. Figure 8.22
El Niño changes atmospheric circulation and weather patterns.
(b) In La Niña years, high atmospheric pressure south of Alaska blocks the storm track. Winds veer north, lose their warmth over Canada, and sweep down as cold blasts. The Pacific Northwest gets its usual rain, but the southwest suffers drought.
Fig. 8-22b, g

84. Fig 8-21b, g

85. North Pole South Pole North Pole South Pole North Pole South Pole0°
North Pole
South Pole
60°W 0°
North Pole
South Pole
60°N
30°N
30°S 0°
60°W
North Pole
South Pole
30°E
30°W
Prime meridien
Latitude
Longitude
Equator
Box 2.1: Latitude and Longitude.
(a) Latitude is measured as the angle between a line from Earth’s center to the equator and a line from Earth’s center to the measurement point. (b) Longitude is measured as the angle between a line from Earth’s center to the measurement point and a line from Earth’s center to the prime (or Greenwich) meridian, which is a line drawn from the North Pole to the South Pole passing through Greenwich, England. (c) Lines of latitude are always the same distance apart, but the distance between two lines of longitude varies with latitude.
Stepped Art