1. The Circulation of the Oceans

2. Key Questions Why do ocean currents form?
How can the circulations of both the surface ocean and the deep ocean basins be driven by solar radiation and be closely linked, yet operate at very different scales?
What role do ocean circulation play in the global climate system?

3. Types of Ocean Circulation
Surface ocean circulation
Moved by winds
Upper m of ocean
Thermohaline circulation
Moved by density differences
Both contribute to
Redistribution of energy in the Earth System
Distribution of nutrients in the ocean

4. SURFACE-OCEAN CIRCULATION
Energy the driving force
Available solar energy drives circulation of atmosphere and ocean
Circulation of ocean linked to circulation of atmosphere by friction
Imbalance in latitudinal distribution of energy creates wind
Currents move due to friction as blowing winds drag the surface along
Force known as wind stress

5. Solar Energy and Oceans
Solar energy warms top few hundred meters of ocean
90% of radiation absorbed in top 100 m of ocean
Unlike atmosphere, oceans do not move directly by temperature gradient
Warm on top, stable
Ocean is stratified wrt temperature (and density and salinity)
Oceans have high heat capacity
Ocean surface temperature influences atmospheric circulation
Resulting winds determines circulation of upper ocean

6. SURFACE CURRENTS

7. CORIOLIS EFFECT Coriolis affects ocean circulation
To the right in Northern Hemisphere
To the left in Southern Hemisphere
Deflection 20-25 from wind direction

8. GYRES Large circular ocean circulation patterns
Combination of Coriolis Effect and continent obstacles

9. EKMAN SPIRAL & TRANSPORT

10. CONVERGENCE & DOWNWELLING

11. DIVERGENCE & UPWELLING
Ekman transport due to the easterly trade winds causes upwelling along the equator.

12. COASTAL DIVERGENCE/UPWELLLING & CONVERGENCE/DOWNWELLING
Coastal upwelling areas across the globe

13. The Ekman Spiral & Upwellng and Downwelling
Bombeamento de Ekman

14. Geostrophic Flow
Ekman transport piles up water within subtropical gyres
Surface water flows downhill and to the right (Northern Hemisphere)
Geostrophic flow – balance of Coriolis Effect and gravitational forces
Ideal geostrophic flow would make water flow in circles within the gyre
Friction generates actual geostrophic flow, slowing the water down so it falls to the outside of the gyre
© 2011 Pearson Education, Inc.

15. GEOSTROPHIC CURRENT

16. BOUNDARY CURRENTS

17. BOUNDARY CURRENTS Western Boundary Currents Eastern Boundary Currents
Narrow
Fast
Eastern Boundary Currents
Diffuse
Slow
Divergent
Upwelling

18. Western Intensification
Top of hill of water displaced toward west due to Earth’s rotation
Western boundary currents intensified in both hemispheres
Faster (100s mi/day)
Narrower (60 mi)
Deeper (up to 1.2 mi)
Warm
Coriolis Effect contributes to western intensification
© 2011 Pearson Education, Inc.

19. THE GULF STREAM – Western Boundary
Narrow – km wide
Warm – 20° C +
Deep – 1 km
Fast – 3-10 km/hr

20. Eastern Boundary Currents
Eastern side of ocean basins
Tend to have the opposite properties of Western Boundary Currents
Cold
Slow (10s of mi/day)
Shallow (0.3 mi)
Wide (600 mi)
© 2011 Pearson Education, Inc.

21. CANARY CURRENT– Eastern Boundary
Slow
Shallow – 500m
Broad – 1000 km

22. SARGASSO SEA
The Sargasso Sea in the North Atlantic is bounded by the Gulf Stream on the west, the North Atlantic Current on the north, the Canary Current on the east, and the North Equatorial Current on the south

23. GREAT PACIFIC GARBAGE PATCH

24. GREAT PACIFIC GARBAGE PATCH
Areas with a higher concentration of plastic
Much of the debris found in these areas are small bits of plastic (microplastics) that are suspended throughout the water column
The debris is more like flecks of pepper floating throughout a bowl of soup, rather than a skim of fat that accumulates (or sits) on the surface

25. VORTICITY
CCW = +
CW = -

26. Ocean Circulation & Sea Surface Temperatures

27. Ocean Circulation & Sea Surface Temperatures
Water moving toward poles warmer that polar ocean
Water moving toward equator colder than tropical ocean
Ocean currents add to latitudinal redistribution of energy
Warmer water moved toward poles, cooler water moved toward equator

28. Ocean Circulation & Sea Surface Temperatures

29. SNEAKER OCEANOGRAPHY

30. Ocean Memory
Ocean absorb & store large amounts of heat & release slowly
Oceans memory of temperature change longer than atmosphere
Oceans most likely to have processes that cause climate anomalies for long periods of time
Where to look?
Tropics
Poles

31. Atmosphere & Ocean Interaction

32. ENSO El Nino-Southern Oscillation event EL Nino – Southern Oscillation
Major shift in tropical Pacific ocean circulation that occurs every 2-10 years
Large changes in circulation of tropical atmosphere
Significant climate anomalies in tropics and midlatitudes
Southern Oscillation
When pressures are low in the western Pacific, they tend to be high in the east
When pressures are high in the western Pacific, they tend to be lower the east

33. Western Pacific – intense convection
Strong easterly winds
Upwelling coastal SA
Heavy precipitation in Australia and Indonesia
La Nina – when normal pattern intensifies
Trade winds weaken/reverse
Western Pacific – build up of warm water
Kelvin wave moves back across ocean (time = 60 days)
Central Pacific warms (convection intense)
Upwelling coastal SA stops (reduces biologic productivity)
Heavy precipitation in central Pacific & western Americas

35. Southern Oscillation Index (SOI)

36. CLLIMATIC IMPACTS OF ENSO

37. 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
Takes about 1,000 years to complete one loop
© 2011 Pearson Education, Inc.

38. SALINITY Total dissolved inorganic solids
A measure of the quantity of elements (Na + Cl, most common) dissolved in a given mass of seawater
g salt / kg seawater
average is 35 PSU (Practical Salinity Units – based on conductivity)
or 35 ppt (parts per thousand, or ‰) or per mil

39. SOURCE OF IONS IN SEAWATER
Weathering of crustal rocks (Na)
4 x 106 tons annually
Outgassing from volcanoes (Cl)
Recirculating in the mantle (at mid ocean ridges)

40. Salinity

41. PRINCIPLE OF CONSTANT PROPORTIONS
Dissolved ions in seawater found in nearly constant proportions worldwide
Exception – ions used by marine organisms
Calcium
Silicon

42. WHY ISN’T THE OCEAN GETTING SALTIER?
Salt is removed:
Evaporation – evaporate deposits
Biological processes – shells
Chemical reactions – with volcanic rock
Sea spray – removed Na + Cl
RESULT -
removal rate = input rate

43. T (Thermocline) + H (Halocline) = P (Pycnocline)
Low Latitudes

44. Western Atlantic

45. Pacific Ocean

46. 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
© 2011 Pearson Education, Inc.

47. Thermohaline Circulation
© 2011 Pearson Education, Inc.

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

49. Thermohaline Circulation
Some bottom water masses
Antarctic Bottom Water (AABW)
North Atlantic Deep Water (NADW)
Antarctic Intermediate Water (AAIW)
Cold surface seawater sinks at polar regions and moves equatorward
© 2011 Pearson Education, Inc.

50. AABW FORAMTION

51. NADW FORMATION

52. Circulation of the Atlantic Ocean

53. AGE OF OCEAN WATER
A parcel of AABW will reemerge at the surface in the Indian Ocean in ~335 yrs and in the Pacific in ~595 yrs
Average residence time in deep ocean is ~500 yrs

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

55. THERMOHALINE CIRCULATION
Water sinking at high latitudes rises somewhere else
Upwelling returns bottom waters to surface
Former deep water moved to poles through surface circulation
Works like giant conveyor belt
Recycles nutrients
Impacts climate

56. Putting it all together ……
© 2011 Pearson Education, Inc.

57. RECYLING NUTRIENTS
Plants and animals living at or near the surface deplete nutrients
Organisms die, sink to the bottom and decompose
Nutrients released
Deep ocean rich in nutrients
Thermohaline circulation distributes nutrients around globe
Upwelling (along continental margins) returns nutrients to surface
Great concentrations of marine life along margins

58. PRODUCTIVITY OF THE OCEAN

59. OCEAN CIRCULATION & CLIMATE
Transport of warm surface water toward pole transfers excess solar energy poleward
Provides almost as much poleward heat transfer as the atmosphere
Transports more heat at low latitudes (Atmosphere transports more at mid- and high latitudes)

60. OCEAN CIRCULATION & CLIMATE

61. OCEAN CIRCULATION & CLIMATE
Oceans are a huge reservoir of heat
Pools of warmer than normal or cooler than normal will cool or warm the atmosphere
Months
Seasons
Years
Based on the rates of bottom water formation, it would take ~1000 yrs to recycle all the water in the oceans
Thermohaline circulation could moderate the climate over time periods of ~ 1000 yrs