1. CHAPTER 7 Ocean Circulation
Fig. CO7

2. Ocean currents Large-scale moving seawater 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
Affect marine life

3. 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

4. Measuring surface currents
Direct methods
Floating device tracked through time
Fixed current meter
Indirect methods
Pressure gradients
Radar altimeters
Satellites measuring bulges which are due to shape of ocean flow and currents
Doppler flow meter (Acoustic Doppler Current Profiler)
Measures shift in frequency of sound waves to determine current movement
Fig. 7.1a

5. Measuring deep currents
Floating devices tracked through time
Chemical tracers (radioactive isotopes)
Tritium
Chlorofluorocarbons
Characteristic temperature and salinity
Arrays of bottom monitors and cables

6. Surface currents Frictional drag between wind and ocean
Wind plus other factors such as…
Distribution of continents
Gravity
Friction
Coriolis effect cause
Gyres or large circular loops of moving water

7. Ocean Gyres World’s 5 subtropical gyres: North Atlantic Gyre
South Atlantic Gyre
North Pacific Gyre
South Pacific Gyre
Indian Ocean Gyre

8. When talking about location of currents, we refer to the ocean basin – not the land!
For instance, the Gulf Stream is a Western Boundary current of the North Atlantic
Even though it runs along side the eastern US

9. Ocean gyres 3 2 4 1 4 2 Subtropical gyres
Center of each is about 30o N or S
Major parts
Equatorial currents flow west
Western Boundary currents flow north or south
Northern or Southern Boundary currents – push water east
Eastern Boundary currents flow north or south 3

10. Other surface currents
Equatorial countercurrents flow east, counter to equatorial currents in the subtropical gyres
As trade winds push equatorial current of subtropical gyre west, water builds up in western part of ocean basin
Since coriolis effect is minimal at equator, that build-up of water then flows east at equator
Subpolar gyres flow eastward
Fig. 7.5

11. Other factors affecting surface currents
Ekman transport
Geostrophic currents
Western intensification of subtropical gyres
All of these are connected
Fig. 7.5

12. Ocean Circulation
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13. Ekman spiral and transport
Surface currents move at angle to wind
Ekman spiral describes speed and direction of seawater flow at different depths
Each successive layer moves increasingly to right (N hemisphere)
Initial push of water and then Coriolis effect comes into play

14. Ekman spiral and transport
Average movement of seawater under influence of wind affected by Coriolis effect
90o to right of wind in Northern hemisphere
90o to left of wind in Southern hemisphere

15. Ekman Spiral and Coastal Upwelling/Downwelling
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16. Geostrophic flow
Ekman transport piles up water within subtropical gyres
Surface water flows downhill (gravity) and
Also to the right (Coriolis effect)
Balance of downhill and to the right causes net geostrophic flow around the “hill”
Fig. 7.8

17. Western intensification
Top of hill of water displaced toward west due to Earth’s rotation
 water piles up on western side of gyre
Western boundary currents intensified
Faster
Narrower
Deeper
Warm

18. Eastern Boundary Currents
Eastern side of ocean basins
Tend to have the opposite properties of Western Currents
Slow
Wide
Shallow
Cold

20. Ocean currents and climate
Warm ocean currents warm air at coast
Creates warm, humid air on coast
Humid climate on adjoining landmass
Cool ocean currents cool air at coast
Cool, dry air
Dry climate on adjoining landmass
August temperatures
February temperatures

21. Ocean currents and climate
August temperatures
February temperatures
Fig. 7.9

22. Diverging surface seawater
Divergence
winds move surface seawater away from geographical equator due to Coriolis effect
Deeper seawater (cooler, nutrient-rich) flows up to replace surface water
Equatorial Upwelling
High biological productivity
Fig. 7.10

23. Converging surface seawater
Convergence
surface seawater moves towards an area
Surface seawater piles up
Nutrient depleted surface water moves downward
Downwelling
Low biological productivity
Occurs at center of gyres
Fig. 7.11

24. Coastal upwelling and downwelling
Winds blowing down coasts
Ekman transport moves surface seawater…
onshore (downwelling) or…
offshore (upwelling)
Fig. 7.12

25. Upwelling at higher latitudes
Remember there is no pycnocline at the poles
Therefore, water moving towards the poles cools and becomes more dense, like all of the other water at the poles
This allows there to be significant vertical mixing
Very productive waters – this is where large animals (such as whales) go to feed

26. Antarctic circulation
Antarctic Circumpolar Current (West Wind Drift)
Encircles Earth
Transports more water than any other current
East Wind Drift from polar easterlies
Antarctic Divergence from opposite directions of west and east wind drifts
Antarctic Convergence piles up and sinks below warmer sub-Antarctic waters
Fig. 7.14

27. Atlantic Ocean circulation
North Atlantic Subtropical Gyre
Gulf Stream (GS)
North Atlantic Current
Canary Current (C)
North Equatorial Current (NE)
Merges with S. Equatorial current to form Antilles and Caribbean currents 
Converge to form Florida Current (F) thru Florida Strait
May form Loop current into Gulf of Mexico
Atlantic Equatorial Counter Current (EC) – between North and South Equatorial currents
No. Atlantic current F

28. North Atlantic Subtropical Gyre
North Atlantic Subtropical Gyre
Sargasso Sea
Center of gyre – eddy
Sargassum “weed” accumulates in convergence
Provides habitat for many marine animals

29. Fig. 7.16

30. Atlantic Ocean circulation
South Atlantic Subtropical Gyre
South Equatorial Current (SE)
Brazil Current (Br)
Antarctic Circumpolar Current (WW)
Benguela Current (Bg)
Fig. 7.14

31. Gulf Stream Best studied
Meander is a bend in current  may pinch off into a loop
Warm-core rings form to north
Cold-core rings form to south
Unique biological populations
Fig. 7.17b

32. Warm core ring Warm core ring forming Cold core rings

33. Core ring vertical profiles

34. Warm core ring off “Loop Current” in the Gulf of Mexico

35. In 2005, winds of Hurricanes Katrina and Rita increase as they pass over warm loop current in Gulf of Mexico

36. Other North Atlantic currents
Labrador Current
Irminger Current
Norwegian Current
North Atlantic Current

37. Climate effects of North Atlantic currents
Gulf Stream warms East coast of U.S. and Northern Europe
North Atlantic and Norwegian Currents warm northwestern Europe
Labrador Current cools eastern Canada
Canary Current cools North Africa coast

38. Pacific Ocean circulation
North Pacific subtropical gyre
Kuroshio
North Pacific Current
California Current
North Equatorial Current
Alaskan Current
Fig. 7.19

39. Figure 7.19

40. Pacific Ocean circulation
South Pacific subtropical gyre
East Australian Current
Antarctic Circumpolar Current
Peru Current
South Equatorial Current
Equatorial Counter Current

41. Relationship of sea surface temp and high altitude pressure
Atmospheric and oceanic disturbances in Pacific Ocean – El Niño-Southern Oscillation (ENSO)
Relationship of sea surface temp and high altitude pressure
Normal conditions
Air pressure across equatorial Pacific is higher in eastern Pacific
Strong southeast trade winds
Pacific warm pool on western side
Thermocline deeper on western side
Upwelling off the coast of Peru bring nutrient-rich waters to surface
As, you are looking at these
figures pay attention to
where thermocline is
(remember that raising
thermocline leads to
upwelling which brings
nutrients and oxygen-rich
waters up to surface for
organisms

42. Normal conditions
Fig. 7.20a

43. El Niño-Southern Oscillation (ENSO)
Warm (El Niño)
High pressure in eastern Pacific weakens
Weaker trade winds
In strong El Nino events, trade winds can actually reverse
Warm pool migrates eastward
Thermocline deeper in eastern Pacific
Downwelling  lowers biological productivity in East Pacific
Corals particularly sensitive to warmer seawater
Fish kills

44. El Niño and La Niña
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45. El Niño-Southern Oscillation (ENSO)
Warm (El Niño)
Produces heavy rains and flooding in equatorial western South America
Droughts in western Pacific
Droughts in Indonesia and Northern Australia

46. Cool phase (La Niña)
Increased pressure difference across equatorial Pacific – overshoots return to normal from El Niño
Stronger trade winds
Stronger upwelling in eastern Pacific
Shallower thermocline
Higher biological productivity
Cooler than normal seawater
Higher than normal hurricane season in Atlantic

47. El Niño-Southern Oscillation (ENSO) Cool phase (La Niña)
Fig. 7.20c

48. ENSO events El Niño warm phase about every 2 to 10 years
Highly irregular
Phases usually last 12 to 18 months
Fig. 7.22

49. ENSO events Fig. 7.21 Strong events effect global weather,
Mild events only effect weather in equatorial South Pacific
, ,
Effects of strong event can vary
Can be drier than normal or wetter than normal
Can be warmer than normal or cooler
Can produce thunderstorms and tornados in midwest
Can produce droughts in west
Pushes jet stream eastward, pushing Atlantic hurricanes east, away from U.S.
Less hurricanes reach US during El Nino, more during La Nina
Flooding, drought, erosion, fires, tropical storms, harmful effects on marine life
Examples: coral reef death in Pacific, crop failure in Philippines, increased cyclones in Pacific, drought in Sri Lanka
Fig. 7.21

50. “Severe” (1997) and “Mild” (2002) El Nino

51. Freeze probability lower during La Nina
Freeze probability slightly higher during El Nino

52. Thermohaline circulation
Caused by density differences due to temp and salinity in different areas
Below the pycnocline
90% of all ocean water
Slow velocity

53. Thermohaline circulation
Bottom water formation
Movement caused by differences in density (temperature and salinity)
Formed by freezing saltwater  dense brine sinks
Cooler seawater denser
Saltier seawater denser

54. Thermohaline circulation
Originates in high latitude surface ocean
Near Greenland & Iceland in North Atlantic
Weddell Sea  Antarctic Bottom Water (coldest)
Forms densest oceanic water  flows on bottom
Moves north in all three ocean basins
Once surface water sinks (high density) it changes little
Deep-water masses identified on T-S diagram

55. Thermohaline circulation
Fig. 7.26

56. Thermohaline circulation
Selected 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

57. Conveyor-belt circulation
Combination deep ocean currents and surface currents
Fig. 7.27

58. Ocean Circulation
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59. Deep ocean currents Cold, oxygen-rich surface water to deep ocean
Dissolved O2 important for life and mineral processes
Deep ocean currents do bring water across the equator
Changes in thermohaline circulation can cause global climate change
Example: warmer surface waters with increased melting of ice caps  less dense surface waters
Bottom water will not form and sink  Gulfstream may be altered  long-term cooling, particularly in northern Europe
less oxygen deep ocean

60. Misconceptions
Earth events taking place within the global environment are not interconnected, such as El Nino is not important to people living in the midwest.
Humans are the only cause of global warming.
The greenhouse effect will cause all living things to die.

61. Ocean Literacy Principles
1c - Throughout the ocean there is one interconnected circulation system powered by wind, tides, the force of the Earth’s rotation (Coriolis effect), the Sun, and water density differences. The shape of ocean basins and adjacent land masses influence the path of circulation.
1d - Sea level is the average height of the ocean relative to the land, taking into account the differences caused by tides. Sea level changes as plate tectonics cause the volume of ocean basins and the height of the land to change. It changes as ice caps on land melt or grow. It also changes as sea water expands and contracts when ocean water warms and cools.
3a - The ocean controls weather and climate by dominating the Earth’s energy, water and carbon systems.
3b - The ocean absorbs much of the solar radiation reaching Earth. The ocean loses heat by evaporation. This heat loss drives atmospheric circulation when, after it is released into the atmosphere as water vapor, it condenses and forms rain. Condensation of water evaporated from warm seas provides the energy for hurricanes and cyclones.
3c - The El Niño Southern Oscillation causes important changes in global weather patterns because it changes the way heat is released to the atmosphere in the Pacific.
3d - Most rain that falls on land originally evaporated from the tropical ocean.
3f - The ocean has had, and will continue to have, a significant influence on climate change by absorbing, storing, and moving heat, carbon and water.
3g - Changes in the ocean’s circulation have produced large, abrupt changes in climate during the last 50,000 years.

62. Sunshine State Standards
SC.8.P.8.4 Classify and compare substances on the basis of characteristic physical properties that can be demonstrated or measured; for example, density, thermal or electrical conductivity, solubility, magnetic properties, melting and boiling points, and know that these properties are independent of the amount of the sample.
SC.912.E.7.2 Analyze the causes of the various kinds of surface and deep water motion within the oceans and their impacts on the transfer of energy between the poles and the equator.
SC.912.P Describe heat as the energy transferred by convection, conduction, and radiation, and explain the connection of heat to change in temperature or states of matter