flow in the upper 1,000 meters of ocean driven by global winds n. and s. hemispheres each have two...
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Ch. 24 The Moving Ocean
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flow in the upper 1,000 meters of ocean
driven by global winds
N. and S. hemispheres each have two circulationscaused by the Coriolis Effectclockwise in N. hemispherecounterclockwise in S. hemisphere
24.1 Surface Currents
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cold currents- move towards the EquatorEastern sides of ocean
basins
warm currents- move towards polesWestern sides of ocean
basins
Current Temperature
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2 sets of global winds drive currentsTrade winds- blow from NE
in N. hemisphere; SE in S. hemisphere
Westerlies- blow from SW in N. hemisphere; NW in S. hemisphere
Earth’s rotation & continents push currents along path of travel
Currents & Winds
Winds
Currents
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Gulf StreamN. AtlanticCanaryN. EquatorialCaliforniaLabradorWest Wind Drift
Important Currents to Know
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flow in opposite direction of wind-related currents
return water taken away from one side of the ocean basin to the opposite sideEX: Equatorial Countercurrents
Countercurrents
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driven by gravity & differences in density
Density current= heavier & denser than surrounding waterSink to bottom from surfacemove very slowlyCirculate for 500-2000 years
24.2 Currents Under the Surface
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global circulation of deep ocean currents
transports warm water to colder areas & cold water to warmer areas
efficient heat-transport system drives Earth’s climate
Global Conveyor Belt
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carry oxygen absorbed from surface for deep sea life
retain same temperature, salinity, & density as surface
turbidity currents are an example of VERTICAL density currents!
Importance of Density Currents
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polar water is the most dense because it’s cold
when water freezes, it leaves behind salt
both of these factors increase density
depth of a water mass or current depends on its density
Density Currents from Polar Water
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increased evaporation leaves salt behind, which increases the density
dense water sinks and is replaced with less dense water
Example: Mediterranean
Density Currents from Evaporation
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vertical density currents that occur when cold deep water comes to the surface
can occur anywhere, prevalent along western coasts of continents
Upwelling
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1. surface winds push water away from continent
2. denser, salty water suddenly sinks
Two Causes of Upwelling
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Benefits of Upwellinglarge amounts of
nutrients come to surface
phytoplankton populations cultivate and provide food for marine life
Large-scale fishing areas
Examples: California, Morocco, southwestern Africa, Peru, western Australia
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twice-daily rise and fall of Earth’s oceans
result of gravitational pulls from moon and sun
reach different levels depending on Earth’s location in relation to moon and sunMoon has a greater effect since it is closerThe closer an object is to another the greater
the gravitational pull.
24.3 TIDES
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Moon’s effect on the tides:
The moon orbits around Earth causes bulges to rotate around the Earth over the lunar month (~29 days).
The moon rises about 50 minutes later each days so do the tides.
24.3 TIDES
Uniform water level
Moon
Moon’s orbit
Low tide
Low tide
Direct high tide
Indirect high tide
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sun can enhance or detract from the moon’s effectsSpring Tides occur when the sun and moon are
in alignment (enhances tides)High tides are higher and low tides are lower
24.3 TIDES
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Neap Tides occur when the sun and moon are at right angle (sun detracts from moon’s pull)High tides are not as high and low tides are not
as low
24.3 TIDES
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24.3 TIDESTidal Range is the difference between high
and low tides.more noticeable on oceans than lakesSmall lakes show no tides at allGreat Lakes have tides with ranges of just a few
centimetersOcean tidal ranges can vary greatly
closer to the poles the greater the tidal range
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24.3 TIDESThe shapes of individual shorelines influence the
tidal rangeA narrow bay has a greater tidal range than a wide
coastal area.
Bay of Fundy, High tide Bay of Fundy, Low tide