1. The Ocean General Circulation (satellite)

2. Biological Productivity in the Ocean

3. Ocean Circulation Learning objectives:
Mass flow of ocean water is driven by two forces - wind (10%) and gravity (90%)
Surface currents are driven by wind – Coriolis effect; Ekman transport
Deep ocean, slow and density driven currents - Thermohaline circulation;
Waves (transmit energy not water mass) and Tides (the longest of all ocean waves)

5. Gulf Stream
Mean Circulation in
the Ocean

7. Gulf Stream
Mean Circulation in
the Ocean
California Current

8. Temperature
Surface
150 meter depth

9. Annual mean Salinity Map

10. Major oceanic circulation systems

11. Gulf Stream, Plankton Bloom (SeaWiFS, AVHRR)

12. Gulf Stream Spiral Eddies

13. Mediterranean Sea, Shear Wall Spiral Eddies

14. Tropical Atlantic, Spiral Eddy

15. Greek Island, Spiral Eddies and Wakes

16. Strait of Gibraltar

17. Kelvin Waves, from Ships

18. Coastal Dynamics California Filaments and Phytoplankton
Hawaiian Island Wakes

19. Some important differences between ocean and atmosphere
Ocean is heated from above
Feels both
Mechanical forcing by the winds
&
Thermal forcing from the sun
Boundaries and complex geometry associated with continents and bottom topography, and bathymetry
Ocean is denser than atmosphere
Tides
Salinity
Atmosphere has clouds and moisture

21. How is the energy of the winds transferred to the ocean?
Ekman Theory …

22. surface 100 meter depth How does wind force propagate in the ocean?
balance between friction and rotation
100 meter
depth

23. 1 2

24. Ekman Theory …and vertical advection in the ocean
COASTAL UPWELLING and DOWNWELLING
OPEN OCEAN EKMAN PUMPING

28. Effects of
Ekman Currents

29. Atmosphere 60 30
Ocean

30. Some practical rules to remember:
Applies to the Ocean same as Atmosphere!
Fpressure
Low Pressure
High Pressure
FCoriolis
Particle will have the Coriolis effect 90 degrees to the right
Particles will tend to move along line of constant pressure
Particles will have the high pressure on their right (same as Coriolis)

31. Sea surface height

33. Arctic sea ice

34. Evidence of Global Warming in the Climate System:
Glacier melting
Kilimanjaro: ice caps are 80% gone since early 1900’s
All glaciers in tropics are melting rapidly
Impacts: water supply, power generation, tourism, local climate and ecology

35. To understand how climate has changed in the past, we need to use records of climate preserved in ice cores, ancient tree rings, coral bands, and other “paleoclimatic” sources:

36. A paleo prospective
CO2
70 ppm
5 C
Temperature

38. Arctic - the most sensitive ecosystem?
Arctic sea ice has shrunk by 1 million sq km and thinned from 3.1m to 1.8m average
More freshwater, reduced ability to travel over ice
All summer ice gone in this century
Ecological consequences huge!

39. Arctic warming 1979 2003 Sea ice melting Warming temperature
Key feedback! (animation)
Reduces albedo (reflectivity) of earth, allowing more radiation to be absorbed
Warming temperature
Melts permafrost
Ice sheet stability? Key sea level question!
Rate of warming 8x faster in last 20 years than in last 100
1979
2003

40. Arctic ecosystems impacts
Reduced ice: less algal production under ice = undermines base of food chain
Seal pups emerge just when ice is melting - earlier melt means they are exposed before ready to thrive
Caribou need ice to island-hop; they are falling through as ice thins
Polar bears hunt on ice in winter, retreat to land in summer. Less ice forces them onto land earlier

41. Higher sea level… As water warms, it expands (“thermal expansion”).
Glaciers are melting
Observation: 3mm/yr in past few decades
Prediction: ~0.5m rise by the end of this century, 2-4m in 500 years
This will have a major impact on
Developed coastal regions
Low-lying island nations
Intensity of coastal flooding during storm surges
Coastal ecosystems (e.g. mangroves, estuaries)

42. More intense storms…
Hurricanes get their energy and staying power from warm water in the tropical oceans.
As waters get warmer, we expect that hurricanes will become more intense.
Significant change not yet observed.

43. Map of predicted temperature change for a doubling of atmospheric CO2
Warmer temperatures…
Prediction: Doubled CO2 will warm the planet by °C (before 2100)
Some areas warm up more than others.
Continents warm faster than oceans.
Higher latitudes warm more than low.
Map of predicted temperature change for a doubling of atmospheric CO2

44. Oceanography and Climate - millennial timescales
Vertical circulation of the ocean
MOVIE:
The Day After Tomorrow

45. Biological Productivity in the Ocean