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Wind-Driven Circulation and Climate Impacts on the Ocean

Explore the role of wind-driven circulation in the ocean and its impact on climate. Learn about surface currents, upwelling and downwelling, the Gulf Stream, and major oceanic circulation systems. Discover how the energy of the winds is transferred to the ocean and its effects on temperature and salinity. Understand the relationship between ocean and atmosphere dynamics and the influence on global climate patterns.

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Wind-Driven Circulation and Climate Impacts on the Ocean

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  1. The Ocean General Circulation (satellite)

  2. Ocean wind driven circulation Learning Objectives How does the wind drive surface currents Upwelling and Downwelling

  3. Gulf Stream Mean Circulation in the Ocean

  4. Gulf Stream Mean Circulation in the Ocean California Current

  5. Annual mean Salinity Map

  6. Dissolved Oxygen Surface 500 meter depth

  7. Major oceanic circulation systems

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

  9. Gulf Stream Spiral Eddies

  10. Mediterranean Sea, Shear Wall Spiral Eddies

  11. Tropical Atlantic, Spiral Eddy

  12. Greek Island, Spiral Eddies and Wakes

  13. Strait of Gibraltar, Solitons

  14. Eastern Pacific Internal Waves

  15. Kelvin Waves, from Ships

  16. Coastal Dynamics California Filaments and Phytoplankton Hawaiian Island Wakes

  17. 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

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

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

  20. 1 2

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

  22. Effects of Ekman Currents

  23. Atmosphere 60 30 Ocean

  24. Sea surface height

  25. Temperature Surface 150 meter depth

  26. 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)

  27. Glacier melting Evidence of Global Warming in the Climate System: • 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

  28. 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!

  29. Arctic warming • Sea ice melting • Key feedback! (animation) Reduces albedo (reflectivity) of earth, allowing more radiation to be absorbed http://www.gsfc.nasa.gov/topstory/2003/1023esuice.html • 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

  30. 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

  31. 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)

  32. 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.

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

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