Ch. 24 The Moving Ocean

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

cold currents- move towards the EquatorEastern sides of ocean

basins

warm currents- move towards polesWestern sides of ocean

basins

Current Temperature

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

Gulf StreamN. AtlanticCanaryN. EquatorialCaliforniaLabradorWest Wind Drift

Important Currents to Know

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

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

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

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

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

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

vertical density currents that occur when cold deep water comes to the surface

can occur anywhere, prevalent along western coasts of continents

Upwelling

1. surface winds push water away from continent

2. denser, salty water suddenly sinks

Two Causes of Upwelling

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

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

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

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

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

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

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