The Ocean General Circulation (satellite)

Biological Productivity in the Ocean

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)

http://www.oceanmotion.org/ http://www.oceanmotion.org/html/resources/etopo.htm

Gulf Stream Mean Circulation in the Ocean

Gulf Stream Mean Circulation in the Ocean California Current

Temperature Surface 150 meter depth

Annual mean Salinity Map

Major oceanic circulation systems

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

Kelvin Waves, from Ships

Coastal Dynamics California Filaments and Phytoplankton Hawaiian Island Wakes

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

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

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

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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 60 30 Ocean

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)

Sea surface height

Arctic sea ice http://maps.grida.no/go/graphic/arctic-sea-ice-minimum-extent-in-september-1982-2005-and-2007 http://maps.grida.no/go/collection/global-outlook-for-ice-and-snow

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

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:

A paleo prospective CO2 70 ppm 5 C Temperature

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! http://www.nytimes.com/interactive/2007/10/01/science/20071002_ARCTIC_GRAPHIC.html#

Arctic warming 1979 2003 Sea ice melting Warming temperature 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

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

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)

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.

Map of predicted temperature change for a doubling of atmospheric CO2 Warmer temperatures… Prediction: Doubled CO2 will warm the planet by 1.8-5.8°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

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

Biological Productivity in the Ocean