The Ocean General Circulation (satellite). Biological Productivity in the Ocean.
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Transcript of The Ocean General Circulation (satellite). Biological Productivity in the Ocean.
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 transportDeep 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
Mean Circulation in the Ocean
Gulf Stream
Mean Circulation in the Ocean
Gulf Stream
California Current
Surface
150 meter depth
Temperature
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 Filamentsand 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
1
2
Ekman Theory …and vertical advection in the ocean
COASTAL UPWELLING and DOWNWELLING
OPEN OCEAN EKMAN PUMPING
Effects of Ekman Currents
Atmosphere
Ocean30
60
Fpressure
FCoriolis
1) Particle will have the Coriolis effect 90 degrees to the right2) Particles will tend to move along line of constant pressure3) 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!
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
Arctic sea ice
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:
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:
CO2
Temperature
70 ppm
A paleo prospective
5 C
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_GRA
PHIC.html#
Arctic warming• Sea ice melting
– Key feedback! (animation)Reduces albedo (reflectivity) of earth,
allowing more radiation to be absorbedhttp://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
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.
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 timescalesVertical circulation of the ocean MOVIE:
The Day After Tomorrow
Biological Productivity in the Ocean