Chapter 21 Ocean Currents
Review
Aimee Thompson
Global Wind Belts
• Trade Winds – located just north and south of the
equator. In Northern Hemisphere, blow from the
northeast. In Southern Hemisphere, blow from
the southeast. In both Hemispheres, trade-wind
belts push currents westward across the tropical
latitudes of all three major oceans.
• Westerlies – located in the middle latitudes.
Northern Hemisphere, blow from the southwest.
Southern Hemisphere, blow from the northwest.
Push ocean currents eastward in higher latitudes
of the Northern and Southern Hemispheres.
Affecting Surface Currents
• Wind – Caused by the uneven heating of the
atmosphere, variations in wind temperature lead to
variations in air density and pressure. Cold, denser,
high pressure = sinks. Kinetic energy transfers to
oceans from the air, and causes movement.
• Continents – Act as barriers against surface currents,
and currents are deflected and divided.
• Coriolis Effect – Earth spins on its axis, ocean currents
and wind belts curve. This curving path of oceans and
winds, due to the Earth’s rotation, is the Coriolis Effect.
The Coriolis Effect causes gyres, huge circles of moving
water, to form.
Major Surface Currents
• Warm equatorial currents – Atlantic, Pacific,
Indian Oceans. Each ocean has two warmwater equatorial currents that move
westward.
• Equatorial Countercurrent – between the
westward warm equatorial currents of the
Atlantic, Pacific, and Indian Oceans. Weaker,
eastward-flowing current.
Gulf Stream
• Swift, deep, and warm Atlantic current that
flows along the east coast of the United States
towards the north.
• Impact – Becomes the North Atlantic current;
splits into two.
Deep Currents
• Cold, dense currents far below the surface.
• Causes – density; polar waters, temperature.
• Location – Deep in the polar water regions.
• Direction of flow – South
• Speed - Slow
Factors of Wave Size
• Fetch – Distance wind can blow across open
water.
• Speed of wind.
• Length of time wind blows.
Breakers
• Foamy.
• Mass of water.
• Washes onto the coastline.
Undertows and Rip Currents
• Motion of irregular currents.
• Large bodies of breakers return to ocean
through cuts in sandbars.
Longshore Currents
• Waves approach the beach at an angle.
Tsunamis
• Not caused by wind.
• Causes:
– Earthquakes;
– Volcanic Eruptions;
– Underwater landslides
Tides
• Periodic rise and fall of water levels in ocean.
• Causes:
– Moon;
– Gravity pulls at water
• Spring Tide – Tidal range during New Moon and
Full Moon.
• Neap Tide – Forces of the sun and moon working
against one another.