The Ocean General Circulation (satellite)

Mean Circulation in the Ocean Gulf Stream

Mean Circulation in the Ocean Gulf Stream California Current

Annual mean Salinity Map

Surface 500 meter depth Dissolved Oxygen

Major oceanic circulation systems

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

Gulf Stream, Plankton Bloom (SeaWiFS, AVHRR)

Gulf Stream Spiral Eddies

Mediterranean Sea, Shear Wall Spiral Eddies

Tropical Atlantic, Spiral Eddy

Greek Island, Spiral Eddies and Wakes

Strait of Gibraltar, Solitons

Eastern Pacific Internal Waves

Kelvin Waves, from Ships

Coastal Dynamics California Filaments and Phytoplankton Hawaiian Island Wakes

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 Some important differences between ocean and atmosphere

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

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

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

Effects of Ekman Currents

Atmosphere Ocean 30 60

Sea surface height

Surface 150 meter depth Temperature

F pressure F Coriolis 1)Particle will have the Coriolis effect 90 degrees to the right 2)Particles will tend to move along line of constant pressure 3)Particles will have the high pressure on their right (same as Coriolis) Some practical rules to remember: High Pressure Low Pressure Applies to the Ocean same as Atmosphere!

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 Evidence of Global Warming in the Climate System:

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!

Arctic warming Sea ice melting –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

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

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) 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

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.

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