Ocean Currents

Chapter 16

Surface Currents A current is the flow of water moving through the

ocean. Surface currents (flow in the upper 1000 m) are

caused by wind.

Surface Currents in the Ocean Warm currents flow from the equator to

the poles, and cold currents flow from the poles to the equator

Surface currents form a circular pattern called a gyre.

Surface Currents in the Ocean

Gyres in the Northern Hemisphere flow clockwise, gyres in the Southern Hemisphere flow counterclockwise.

Surface Currents in the Ocean West sides of oceans

have warm ocean currents that flow away from the equator.

East sides of oceans have cold ocean currents that flow to the equator.

Surface Currents & Wind The earth rotates in

an easterly direction. This makes the winds

blowing toward the equator curve westward, and the winds blowing toward the poles curve eastward.

Surface Currents and Winds

Trade winds drive the equatorial part of the ocean currents.

They blow from the east, towards the west.

The westerly winds drive the polar part of the ocean currents.

They blow from the west, towards the east.

Surface Currents and Winds

Deep Currents

Because the warm surface water and cold deep waters don’t mix, surface currents have little effect on the deep ocean water.

Deep currents are caused by density differences. Remember, cold water is more

dense than warm water!

Deep Current Movement The densest water is at the poles. As ice forms, the salt is left behind, leading

to high-salinity, dense water. This water sinks to the deep ocean (deep

water masses). Water flows from high density to low

density, and moves from the poles toward the equator.

Upwelling When wind blows parallel to a shoreline,

surface currents and deep currents can mix.

The wind pushes the warm water away from the coast, and cold deep water takes its place.

This upward movement of cold water is called upwelling.

Where upwelling occurs, the water is rich with nutrients that it brings up from the ocean floor.

Upwelling

Shoreline Currents A longshore current forms when waves

approach a shore at an angle.

Rip Currents A rip current forms when water that is built up

behind a sandbar due to a longshore current finally breaks through.