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Module F: Unit 2, Lesson 3 – Ocean Currents
What are ocean currents?
• Ocean currents are streamlike movements of water in the ocean.
• Surface currents are ocean currents that occur at or near the surface of the ocean,
caused by wind.
• The Gulf Stream is one of the strongest surface currents on Earth.
What affects surface currents?
• Surface currents are affected by continental deflections, the Coriolis effect, and
global winds.
• When surface currents meet continents, they are deflected and change direction.
• The deflection of moving objects from a straight path due to Earth’s rotation is
called the Coriolis Effect.
• In the Northern Hemisphere, currents are deflected to the right.
• In the Southern Hemisphere, currents are deflected to the left.
• Global winds can push ocean water across Earth’s surface to create surface
currents.
What powers surface currents?
• The major source of energy that powers surface currents is the sun.
• The sun heats air near the equator more than it heats air at other latitudes. As a
result, there are differences in pressure in the atmosphere.
• Winds form as a result of differences in air pressure and create surface currents.
How do deep currents form?
• Deep currents are movements of ocean water far below the surface. They are
caused by differences in water density.
• Density is the amount of matter in a given space or volume.
• Salinity and temperature cause differing ocean water densities.
• Salinity is a measure of the amount of dissolved salts or solids in a liquid. Higher
salinity makes water more dense.
• Cold water is denser than warm water.
• Dense water sinks and can form deep water currents that flow along the ocean
floor or on another layer of denser water.
What are convection currents?
• Convection currents in the ocean are the movement of water that results from
density differences.
• Convection currents can be vertical, circular, or cyclical.
How do convection currents transfer energy?
• Water at the ocean’s surface absorbs energy from the sun, and surface currents
carry this energy to colder regions.
• As warm water reaches a colder region, it cools, becomes denser, and sinks.
• As warm surface water moves away, cold water rises to the surface. The cold
water absorbs the sun’s energy, and the cycle continues.
What is upwelling?
• Upwelling is the process by which winds blow warm water away from a shore,
allowing cool, nutrient-rich water to rise to the surface.
• Upwelling supplies the nutrients that support the growth of phytoplankton and
zooplankton.
• These tiny organisms are food for larger organisms, such as fish and seabirds.
Hitching a Ride!
• Ocean currents can transport various living organisms to different parts of the
world.
• Turtles, coconuts, and phytoplankton all ride the ocean’s surface currents.
What do ocean currents transport?
• Convection currents in the ocean transport energy in the form of heat.
• Ocean currents can release energy into the atmosphere, making currents an
important influence on climate.
• Ocean water also transports dissolved solids, including nutrients, and dissolved
gases that support the growth of many marine organisms.