U5 - Lesson 5: Deep Ocean Currents

Unit 5: Oceanography
Lesson 5 - Deep Ocean Currents

Ocean Temperature Variation

•The ocean’s surface water temperature varies with the amount of sunlight received, which depends on latitude (direct or indirect sunlight).

Thermocline

•The thermocline lies below the surface layer. The water temperature here drops fast with depth (300-1000 meters).

Deep Water

•Deep water is cold all year round. The bottom of the ocean is around 0 degrees Celsius (slightly above freezing). It is the same almost anywhere in the globe, even in the topics. 

Deep-Ocean Circulation

•Deep-ocean water currents are set in motion by differences in density.

Density Currents

•The density of seawater is affected by temperature and salinity. As the water cools due to the lack of direct sunlight when it reaches the poles, ice forms such as ice burgs (fresh water). The colder, saltier water is dense and sinks. Deep currents carry cold, dense water toward the equator. As the water warms, it becomes less dense and rises.

Example: North Atlantic Deep Water

•Cold, dense water around Labrador, Canada form this deep ocean current.

Multiple Choice

The density of seawater is affected by ____ and ____.

• temperature and salinity

• temperature and upwelling

• salinity and waves

• salinity and gyres

Multiple Choice

Deep ocean currents are set in motion by ____.

• winds

• topography

• earthquakes

• density differences

Multiple Choice

Where does the cold, dense saltier water come from?

• cold wind

• warm, surface water from the equator

• cold surface water from the equator

• polar ice caps

Multiple Choice

Surface water temperature varies depending on what?

• longitude and direct sunlight it receives

• latitude and direct sunlight it receives

• longitude and indirect sunlight it receives

• latitude and indirect sunlight it receives

Multiple Choice

The area where the water temperature drops drastically is known as what?

• density difference

• upwelling

• thermocline

• indirect sunlight