Ocean currents are driven by both wind at the surface and density differences in deep water. Surface currents move large amounts of heat and water around the world's oceans. Below the surface, thermohaline circulation involves the slow movement of dense water masses that sink and flow horizontally, driven by differences in water density due to temperature and salinity. Together, surface and deep ocean currents form the global conveyor belt that redistributes heat around the planet.

1. Chapter 8: Ocean Circulation
Fig. 8-26

2. Ocean currents move large
amounts of water and heat
 Wind-driven
surface ocean
circulation
 Density-driven
deep-ocean
circulation
 Both redistribute
heat from warmer
regions to cooler
Fig. 8-16

3. Measuring ocean currents
 Direct measurement
 Floating objects/instruments
 Fixed instruments
 Indirect measurement
 Distribution of density
 Satellite data
 Doppler flow meter
 Chemical tracers
 Distinctive water masses

7. Surface currents
 Frictional drag due to winds
 Surface currents similar to global winds
 Continents affect surface current
patterns
 Other factors:

Gravity

Friction

Coriolis Effect

9. Subtropical gyres
 Large circular flow
 Clockwise in northern oceans,
e.g., North Atlantic
 Counterclockwise in southern
oceans, e.g., South Atlantic
 4 main currents in each gyre

11. Ekman spiral and Ekman
transport  Ekman transport
moves surface
seawater about
90o
to the right of
the wind in the
Northern
Hemisphere
 90o
left in
Southern
Hemisphere
Fig. 8-6a

13. Western intensification
 “Hill” of seawater is steeper on western side
 Western currents are fast, narrow, deep

14. Subtropical gyres
 Ekman transport
piles up “hill” of
seawater at about
30o
N and S
 Water flows downhill
under gravity and
veers right (Northern
hemisphere) due to
Coriolis Effect
 Circular flow Fig. 8-7

15. Upwelling
 Ekman transport
moves seawater
offshore
 Ekman transport
moves seawater
away from
another water
mass
Fig. 8-11a

16.  Cooler, nutrient-
rich water rises
vertically toward
sea surface
 High biologic
productivity
 Downwelling
opposite
Fig. 8-11b

18. Surface currents
 Pattern similar in major ocean
basins
 Northern ocean gyre moves
clockwise
 Southern ocean gyre moves
counter-clockwise

19. Antarctic circulation
 Antarctic Circumpolar Current (or
West Wind Drift)
 Greatest volume
 Connects main oceans
 East Wind Drift
 Antarctic Divergence (upwelling)

20. North Atlantic Circulation
 North Equatorial Current
 Gulf Stream
 North Atlantic Current
 Gulf Stream and North Atlantic
Currents warm Europe
 Canary Current

21. North Equatorial Current

22. Gulf Stream

23. North Atlantic Current

24. Canary Current

25. South Atlantic Ocean
 South Equatorial Current
 Brazil Current
 Antarctic Circumpolar Current
 Greatest volume
 Connects three main oceans
 Benguela Current

26. South Equatorial current

27. Brazil Current

28. Benguela Current

29. North Pacific Ocean
 North Equatorial Current
 Kuroshio Current
 North Pacific Current
 California Current
 Strong Equatorial Counter Current

30. South Pacific Ocean
 South Equatorial Current
 East Australian Current
 Antarctic Circumpolar Current
 Peru Current
 Strong Equatorial Counter Current

31. ENSO El Niño-Southern
Oscillation
 Irregular shift in ocean and
atmosphere characteristics every 2-
10 years
 Affects global climate
 Harmful and beneficial
consequences

32. El Niño ENSO Warm Phase
 Most obvious in Equatorial Pacific
 Pacific Warm Pool moves eastward across
Equatorial Pacific
 Changes in pattern of upwelling/downwelling
in eastern Pacific Ocean
Fig. 8-2

33. ENSO warm phase effects
 Warmer seawater higher sea level
 Warmer seawater less upwelling in
eastern Pacific
 Lower biologic productivity
 Warmer seawater kills some marine life
 Shift in atmosphere pressure
 Shift in areas of precipitation

37. La Niña ENSO Cool Phase
 Stronger tradewinds
 Warm pool stays in western Pacific
 Increased upwelling in eastern Pacific
 Shift in precipitation patterns
 Shift in atmospheric pressure

38. ENSO data collection
 TOGA Tropical Ocean Global
Atmosphere
 TAO Tropical Atmosphere Ocean
 Monitor ocean and atmosphere
 Data indicate what phase ENSO
 Pacific Decadal Oscillation
 Decades-long cycles of warming
and cooling in Pacific Ocean

39. Indian Ocean Circulation
 North and South Equatorial Currents
 Equatorial Counter Current
 Agulhas Current
 Antarctic Circumpolar Current
 West Australian
 Seasonal shifts (monsoons) of winds
and currents

42. Thermohaline circulation
 90% of world ocean
 Below pycnocline
 Large volumes of
seawater
 Extremely slow
speed
 Each ocean basin is
similar in deep-
ocean circulation

43. Sources of deep water
 Densest seawater is cold
 Most deep water masses from
polar oceans
 Sink to density level and move
horizontally

44. Antarctic Bottom Water
 Densest deep water
(coldest)
 Sinks around
Antarctica
 Most widespread
deep-water mass
 Found as far as
40o
N
 Carries O2 into deep
ocean Fig. 8-25

45. North Atlantic Deep Water
 Complex mixture
of cold seawater
from Norwegian
sea mixing with
 Gulf Stream
 Mediterranean
Intermediate
Water
 Other NA water
masses
 Extends from
North Atlantic to
about 40o
south

46. Intermediate Water Masses
 Antarctic Intermediate Water
 Sinks at Antarctic Convergence
 Cold
 Salinity less than average
 Mediterranean Intermediate Water
 Warm
 Very salty

47. Conveyor Belt Circulation
 Mixture of surface
ocean circulation
and deep-ocean
circulation
 Mixes surface
and deep
 Mixes waters in
different oceans Fig. 8-26

48. Langmuir Circulation
 Alternately converging and diverging
convection cells
 Wind blowing over calm ocean
 Alternate rows of upwelling and downwelling

49. End of Chapter 8: Ocean
Circulation