Ch 7-Circulation 2016b.pptx - Ocean Circulation CHAPTER 7...

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Ocean Circulation CHAPTER 7
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Ocean currents Currents - moving seawater 2% of wind energy transferred to ocean surface Surface currents slower speed than corresponding winds Surface ocean currents Transfer heat from warmer to cooler areas Similar pattern of major wind belts Affect coastal climates Deep ocean currents Provide oxygen to deep sea Affect supply of nutrients and types and numbers of marine life
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Types of ocean currents Surface currents Wind-driven Primarily horizontal motion Deep currents - Driven by differences in density caused by differences in temperature and salinity Vertical and horizontal motions - warming.com/images/thermohaline.jpg
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Measuring surface currents Direct methods Floating device tracked through time Fixed current meter Indirect methods Pressure gradients Radar altimeters Doppler flow meter Fig. 7.1
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Incidental float “meters” Floating objects can act as drift meters Drift seeds “sea beans” Bottle messages (MIB) Objects accidentally lost from cargo containers off of freighters (Worldwide, about a thousand containers are lost overboard each year) Can travel great distances
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Measuring surface currents TOPEX/Poseidon Radar Altimeter Red areas - higher than normal sea level Blue areas – lower than normal sea level Fig. 7.2
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Floating devices tracked through time Argo Global array of free-drifting profiling floats Measuring Deep Currents
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Measuring deep currents Identifying characteristic salinity and temperature layers Naturally occurring chemical tracers
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Tracking Deep-water Movements Chemical Tracers – Introduced by human activity Chlorofluorocarbons – Freon etc. Tritium – radioactive hydrogen isotope Added through nuclear bomb testing Map of 3He concentrations in the Pacific Ocean used as a global plume tracer. Tracking tritium
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Origin of surface currents Frictional drag between wind and ocean Wind plus other factors such as Distribution of continents Gravity Friction against landmasses Coriolis effect causes Gyres - large circular loops of moving water
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Ocean gyres 5 Subtropical gyres Centered about 30 o N or S Major components 1. Equatorial currents flow west 2. Western Boundary currents flow away from the equator 3. Northern or Southern Boundary currents 4. Eastern Boundary currents flow toward the equator 1 2 3 4 3 2 4
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Other surface currents Equatorial countercurrents flow east, counter to equatorial currents Subpolar gyres flow eastward Fig. 7.5
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Other factors affecting surface currents Ekman transport Geostrophic currents Western intensification of subtropical gyres Fig. 7.5
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Ocean Circulation
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Ekman transport Surface currents move at angle to wind Observation that Arctic Ocean ice moved at a 20 to 40-degree angle to the right of the wind Ekman spiral describes speed and direction of seawater flow at different depths Each successive layer moves increasingly to right (N hemisphere) Fig. 7.6
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  • Spring '14
  • Atlantic Ocean, Pacific Ocean, Physical oceanography, Thermohaline circulation, OCEAN CURRENTS, subtropical gyres

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