Chapter 21 Ocean CurrentsReview

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 warm-water 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.