Chapter 7

Chapter 7 - Intro to Oceanography: Chapter 7 Ocean currents...

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Intro to Oceanography : Chapter 7 Ocean currents – masses of ocean water that flow from one place to another (water masses in motion) I. How Are Ocean Currents Measured? a. Ocean currents are either wind driven or density driven. i. Wind – surface currents (horizontal) ii. Density – deep currents (vertical) iii. Surface Current Measurement 1. Direct Methods a. Floating device is released to a current and tracked through time b. Propeller flow meter (fixed position or towed behind a ship) 2. Indirect Methods a. Water flows parallel to a pressure gradient b. Radar altimeters to determine the lumps and bulges at the ocean surface i. Dynamic topography maps can be produced that show the speed and direction of surface currents c. Doppler flow meter to transmit low-frequency sound signals through the water which measures the shift in frequency between the sound waves emitted and those backscattered by particles in the water to determine current movement iv. Deep Current Measurement 1. Often mapped using devices that are carried with the current or by tracking telltale chemical tracers 2. Some useful tracers include tritium (a radioactive isotope of hydrogen produced by nuclear bomb tests in the 1950s and 1960s) and chlorofluorocarbons (freons and other gases now thought to be depleting the ozone layer) II. How Are Ocean Surface Currents Organized? a. Surface currents occur within and above the pycnocline (layer of rapidly changing density) to a depth of about 1 km and affect only about 10% of the world’s ocean water b. Origin of Surface Currents i. Only about 2% of the wind’s energy is transferred to the ocean surface ii. Gravity, friction, and the Coriolis effect influence surface currents. c. Main Components of Ocean Surface Circulation i. Subtropical Gyres 1. Gyre – large, circular-moving loops of water that are driven by the major wind belts of the world
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2. 5 Subtropical Gyres: (1) the North Atlantic Gyre, (2) the South Atlantic Gyre, (3) the North Pacific Gyre, (4) the South Pacific Gyre, and (5) the Indian Ocean Gyre 3. The center of each gyre coincides with the subtropics at 30 degrees latitude 4. Rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere 5. Each subtropical gyre is composed to four main currents that flow progressively into one another a. The North Atlantic Subtropical Gyre is composed of the North Equatorial Current, the Gulf Stream, the North Atlantic Current, and the Canary Current 6. Equatorial Currents a. Equatorial currents – currents from trade winds which travels westward along the equator and form the equatorial boundary current of subtropical gyres 7. Western Boundary Currents a. Western boundary currents – equatorial currents are deflected when it reaches the western portion of an ocean basin by the Coriolis effect (ex: Gulf Stream) 8. Northern or Southern Boundary Currents a. Between 30 and 60 degrees, the prevailing westerlies blow directing ocean surface water in an easterly
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Chapter 7 - Intro to Oceanography: Chapter 7 Ocean currents...

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